The patients with the long QT syndrome type-1 (LQT-1) have an impaired adaptation of the QT interval to heart rate changes. Yet, the description of the dynamic QT/RR coupling in genotyped LQT-1 has never been thoroughly investigated.
We propose a method to model the dynamic QT/RR coupling by defining a transfer function characterizing the relationship between a QT interval and its previous RR intervals measured from ambulatory Holter recordings. Three parameters are used to characterize the QT/RR coupling: a fast gain (GainF), a slow gain (GainL), and a time constant (τ). We investigated the values of these parameters across genders, and in genotyped LQT-1 patients with normal QTc interval duration (QTc<470 ms).
The QT/RR dynamic profiles are significantly different between LQT-1 patients (97) and controls (154): LQT-1 have longer QTc interval (453±35 vs. 384±26 ms, p<0.0001), and an increased dependency of the QT interval to previous RR changes revealed by a larger GainL (0.22±0.06 vs. 0.18±0.07, p<0.0001) and GainF (0.05±0.02 vs. 0.03±0.01, p<0.0001). Importantly, LQT-1 patients have a faster QT dynamic response to previous RR changes described by τ: 122±44 vs. 172±92 beats (p<0.0001). This faster QT dynamic response of the QT-RR dynamic coupling remained in LQT-1 patients with QTc in a normal range (<430 ms).
The measurement of QT/RR dynamic coupling could be used in patients suspected to carry a concealed form of the LQT-1 syndrome, or to provide insights into the types of arrhythmogenic triggers a patient may be prone to.
Long QT syndrome; Dynamic QT/RR coupling; Holter recording; QT adaptation; QT parameters
The goal of this study was to determine the predictive value of beat-to-beat QT variability in heart failure (HF) patients across the continuum of left ventricular dysfunction.
Methods and Results
Beat-to-beat QT variability index (QTVI), heart rate variance (LogHRV), normalized QT variance (QTVN), and coherence between heart rate variability and QT variability have been measured at rest during sinus rhythm in 533 participants of the Muerte Subita en Insuficiencia Cardiaca (MUSIC) HF study (mean age 63.1±11.7; males 70.6%; LVEF >35% in 254 [48%]) and in 181 healthy participants from the Intercity Digital Electrocardiogram Alliance (IDEAL) database. During a median of 3.7 years of follow-up, 116 patients died, 52 from sudden cardiac death (SCD). In multivariate competing risk analyses, the highest QTVI quartile was associated with cardiovascular death [hazard ratio (HR) 1.67(95%CI 1.14-2.47), P=0.009] and in particular with non-sudden cardiac death [HR 2.91(1.69-5.01), P<0.001]. Elevated QTVI separated 97.5% of healthy individuals from subjects at risk for cardiovascular [HR 1.57(1.04-2.35), P=0.031], and non-sudden cardiac death in multivariate competing risk model [HR 2.58(1.13-3.78), P=0.001]. No interaction between QTVI and LVEF was found. QTVI predicted neither non-cardiac death (P=0.546) nor SCD (P=0.945). Decreased heart rate variability (HRV) rather than increased QT variability was the reason for increased QTVI in this study.
Increased QTVI due to depressed HRV predicts cardiovascular mortality and non-sudden cardiac death, but neither SCD nor excracardiac mortality in HF across the continuum of left ventricular dysfunction. Abnormally augmented QTVI separates 97.5% of healthy individuals from HF patients at risk.
ECG; ejection fraction; heart failure; sudden death; QT variability
The objective of this work was to investigate whether fibrinolysis plays a role in establishing recurrent coronary event risk in a previously identified group of postinfarction patients. This group of patients was defined as having concurrently high levels of high-density lipoprotein cholesterol (HDL-C) and C-reactive protein (CRP) and was previously demonstrated to be at high-risk for recurrent coronary events. Potential risk associations of a genetic polymorphism of plasminogen activator inhibitor-2 (PAI-2) were probed as well as potential modulatory effects on such risk of a polymorphism of low-density lipoprotein receptor related protein (LRP-1), a scavenger receptor known to be involved in fibrinolysis in the context of cellular internalization of plasminogen activator/plansminogen activator inhibitor complexes. To this end, Cox multivariable modeling was performed as a function of genetic polymorphisms of PAI-2 (SERPINB, rs6095) and LRP-1 (LRP1, rs1800156) as well as a set of clinical parameters, blood biomarkers, and genetic polymorphisms previously demonstrated to be significantly and independently associated with risk in the study population including cholesteryl ester transfer protein (CETP, rs708272), p22phox (CYBA, rs4673), and thrombospondin-4 (THBS4, rs1866389). Risk association was demonstrated for the reference allele of the PAI-2 polymorphism (hazard ratio 0.41 per allele, 95% CI 0.20-0.84, p=0.014) along with continued significant risk associations for the p22phox and thrombospondin-4 polymorphisms. Additionally, further analysis revealed interaction of the LRP-1 and PAI-2 polymorphisms in generating differential risk that was illustrated using Kaplan-Meier survival analysis. We conclude from the study that fibrinolysis likely plays a role in establishing recurrent coronary risk in postinfarction patients with concurrently high levels of HDL-C and CRP as manifested by differential effects on risk by polymorphisms of several genes linked to key actions involved in the fibrinolytic process.
β-adrenergic stimulation is the main trigger for cardiac events in type-1 long QT syndrome (LQT1). We evaluated a possible association between ion channel response to β-adrenergic stimulation and clinical response to β-blocker therapy according to mutation location.
Methods and Results
The study sample comprised 860 patients with genetically-confirmed mutations in the KCNQ1 channel. Patients were categorized into carriers of missense mutations located in the cytoplasmic loops (C-loops), membrane spanning domain, C/N-terminus, and non-missense mutations. There were 27 aborted cardiac arrest [ACA] and 78 sudden cardiac death [SCD] events from birth through age 40 years. After multivariable adjustment for clinical factors, the presence of C-loop mutations was associated with the highest risk for ACA or SCD (hazard ratio [95% confidence interval] vs. non-missense mutations = 2.75 [1.29-5.86, P=0.009]). β-blocker therapy was associated with a significantly greater reduction in the risk of ACA or SCD among patients with C-loop mutations than among all other patients (hazard ratios = 0.12 [0.02-0.73, P=0.02] and 0.82 [0.31-2.13, P=0.68], respectively; P-for interaction = 0.04). Cellular expression studies showed that membrane spanning and C-loop mutations produced a similar decrease in current, but only C-loop mutations showed a pronounced reduction in channel activation in response to β-adrenergic stimulation.
Patients with C-loop missense mutations in the KCNQ1 channel exhibit a high-risk for life-threatening events and derive a pronounced benefit from treatment with β-blockers. Reduced channel activation following sympathetic activation can explain the increased clinical risk and response to therapy in patients with C-loop mutations.
beta-blockers; ion channels; long QT syndrome; mutation
Current clinical diagnosis of long-QT syndrome (LQTS) includes genetic testing of family members of mutation positive patients. The present study was designed to assess the clinical course of individuals who are found negative for the LQTS-causing mutation in their families.
Methods and Results
Multivariate Cox proportional hazards model was used to assess the risk for cardiac events (comprising syncope, aborted cardiac arrest [ACA], or sudden cardiac death [SCD]) from birth through age 40 years among 1828 subjects from the LQTS Registry who were found negative for their family LQTS-causing mutation. The median QTc of study subjects was 423 msec (interquartile-range: 402–442 msec). The cumulative probability of a first syncope through age 40 years was 15%. However, only 2 patients (0.1%) experienced ACA and none died suddenly during follow-up. Independent risk factors for syncope in genotype negative subjects included female gender (HR 1.60, p = 0.002), prolonged QTc (HR = 1.63 per 100 msec increment, p = 0.02), family history of ACA or SCD (HR = 1.89, p = 0.002), and LQT2 vs. LQT1 family mutation (HR = 1.41, p = 0.03). Subgroup analysis showed that the presence of the K897T polymorphism in the LQT2 gene in an affected family was associated with an 11-fold (p = 0.001) increase in the risk of recurrent syncope in genotype negative subjects.
Our findings suggest that cardiac events among genotype-negative family members of LQTS patients are dominated by nonfatal syncopal episodes without occurrence of sudden cardiac death. The risk for nonfatal events in this population may be mediated by the presence of common polymorphisms in LQTS genes.
gene mutation; genetic polymorphisms; long-QT syndrome; sudden cardiac death arrhythmia; syncope
Post-myocardial infarction (MI) structural remodeling is characterized by left ventricular dilatation, fibrosis, and hypertrophy of the non-infarcted myocardium.
The goal of our study was to quantify post-MI electrical remodeling by measuring the sum absolute QRST integral (SAI QRST). We hypothesized that adverse electrical remodeling predicts outcomes in MADIT II study participants.
Baseline orthogonal ECGs of 750 MADIT II study participants (448 [59.7%] ICD arm) were analyzed. SAI QRST was measured as the arithmetic sum of absolute QRST integrals over all three orthogonal ECG leads. The primary endpoint was defined as sudden cardiac death (SCD) or sustained ventricular tachycardia (VT)/ventricular fibrillation (VF) with appropriate ICD therapies. All-cause mortality served as a secondary endpoint.
Adverse electrical remodeling in post-MI patients was characterized by wide QRS, increased magnitudes of spatial QRS and T vectors, J-point deviation, and QTc prolongation. In multivariable Cox regression analysis after adjustment for age, QRS duration, atrial fibrillation, New York Heart Association heart failure class and blood urea nitrogen, SAI QRST predicted SCD/VT/VF (HR 1.33 per 100 mV*ms (95%CI 1.11–1.59); P = 0.002), and all-cause death (HR 1.27 per 100 mV*ms (95%CI 1.03–1.55), P = 0.022) in both arms. No interaction with therapy arm and bundle branch block (BBB) status was found.
In MADIT II patients, increased SAI QRST is associated with increased risk of sustained VT/VF with appropriate ICD therapies and all-cause death in both ICD and in conventional medical therapy arms, and in patients with and without BBB. Further studies of SAI QRST are warranted.
This study was designed to evaluate the clinical and prognostic aspects of long QT syndrome-related cardiac events that occur in the first year of life (infancy).
The clinical implications for patients with long QT syndrome who experience cardiac events in infancy have not been studied previously.
The study population of 3,323 patients with QTc ≥ 450 ms enrolled in the International LQTS Registry involved 20 patients with sudden cardiac death (SCD), 16 patients with aborted cardiac arrest (ACA), 34 patients with syncope, and 3,253 patients who were asymptomatic during the first year of life.
The risk factors for a cardiac event among 212 patients who had an ECG recorded in the first year of life included QTc≥500ms, heart rate ≤100bpm, and female sex. ACA before age 1 year was associated with a hazard ratio of 23.4 (p<0.01) for ACA or SCD during age 1-10 years. During the 10-year follow-up after infancy, beta-blocker therapy was associated with a significant reduction in ACA/SCD only in those with a syncopal episode within 2 years before ACA/SCD, but not for those who survived ACA in infancy.
Patients with LQTS who experience ACA during the first year of life are at very high-risk for subsequent ACA or death during their next 10 years of life, and beta-blockers may not be effective in preventing fatal or near fatal cardiac events in this small but high-risk subset.
Long QT Syndrome; Genetics; Infants; Risk Stratification
Background: Mechanisms underlying previously reported air pollution and cardiovascular (CV) morbidity associations remain poorly understood.
Objectives: We examined associations between markers of pathways thought to underlie these air pollution and CV associations and ambient particle concentrations in postinfarction patients.
Methods: We studied 76 patients, from June 2006 to November 2009, who participated in a 10-week cardiac rehabilitation program following a recent (within 3 months) myocardial infarction or unstable angina. Ambient ultrafine particle (UFP; 10–100 nm), accumulation mode particle (AMP; 100–500 nm), and fine particle concentrations (PM2.5; ≤ 2.5 μm in aerodynamic diameter) were monitored continuously. Continuous Holter electrocardiogram (ECG) recordings were made before and during supervised, graded, twice weekly, exercise sessions. A venous blood sample was collected and blood pressure was measured before sessions.
Results: Using mixed effects models, we observed adverse changes in rMSSD [square root of the mean of the sum of the squared differences between adjacent normal-to-normal (NN) intervals], SDNN (standard deviation of all NN beat intervals), TpTe (time from peak to end of T-wave), heart rate turbulence, systolic and diastolic blood pressures, C-reactive protein, and fibrinogen associated with interquartile range increases in UFP, AMP, and PM2.5 at 1 or more lag times within the previous 5 days. Exposures were not associated with MeanNN, heart-rate–corrected QT interval duration (QTc), deceleration capacity, and white blood cell count was not associated with UFP, AMP, and PM2.5 at any lag time.
Conclusions: In cardiac rehabilitation patients, particles were associated with subclinical decreases in parasympathetic modulation, prolongation of late repolarization duration, increased blood pressure, and systemic inflammation. It is possible that such changes could increase the risk of CV events in this susceptible population.
air pollution; cardiac rehabilitation; fibrinogen; heart rate variability; repolarization
There is a consensus on the limited value of QT/QTc prolongation as a surrogate marker of drug cardiotoxicity and as a risk stratifier in inherited LQTS patients.
We investigated the interest of repolarization morphology in the acquired and the inherited LQTS.
We analyzed two retrospective ECG datasets from healthy on/off moxifloxacin, and from genotyped KCNH2 patients. We measured QT, RR and T peak to T end intervals, early (ERD) and late repolarization duration, T-roundness, T-amplitude, left (αL) and right slopes of T-waves. We designed multivariate logistic models to predict the presence of the KCNH2 mutation or moxifloxacin while adjusting for the level of QTc prolongation and the level of heart-rate in LQT2 patients. Independent learning and validation sets were used. A list of 4,874 ECGs from 411 healthy individuals, 293 ECGs from 143 LQT2 carriers and 150 non-carrier family members were analyzed.
In the moxifloxacin model, ERD was associated with the presence of the drug (OR=1.15 per ms increase, CI:1.04-1.26, p=0.0001) after adjustment for QTc. The model for the LQT2 revealed that left slope was associated with the presence of the KCNH2 mutation (OR=0.38 per 1.5microV/ms decrease, CI:0.23-0.64, p=0.0002). Only T-roundness complemented QTc in the model investigating cardiac events in LQT2.
These observations demonstrate that the phenotypic expression of KCNH2 mutations and the effect of IKr-inhibitory drug on the surface ECG are specific. Future research should investigate if this phenomenon is linked to different level/form of loss functions of Ikr channels, and if they could result in different arrhythmogenic mechanisms.
Electrocardiogram; long QT syndrome; moxifloxacin; thorough QT studies; KCNH2
Women with congenital long-QT syndrome (LQTS) experience increased risk for cardiac events after the onset of adolescence, that is more pronounced among carriers of the LQT2 genotype. We hypothesized that the hormonal changes associated with menopause may affect clinical risk in this population.
Methods and Results
We used a repeated events analysis to evaluate the risk for recurrent syncope during the menopause-transition and post-menopausal periods (5-years before and after the age at onset of menopause, respectively) among 282 LQT1 (n=151) and LQT2 (n=131) women enrolled in the LQTS Registry. Multivariate analysis showed that the risk for recurrent syncope (n=150) among LQT2 women was significantly increased during both menopause-transition (HR = 3.38 [p = 0.005]) and the post-menopausal period (HR = 8.10 [p < 0.001]) as compared with the reproductive period. The risk increase was evident among women who did or did not receive estrogen therapy. In contrast, among LQT1 women the onset of menopause was associated with a reduction in the risk for recurrent syncope (HR = 0.19 [p = 0.05]; p-value for genotype-by-menopause interaction = 0.02). Only 22 women (8%) experienced aborted cardiac arrest (ACA) or sudden cardiac death (SCD) during follow-up. The frequency of ACA/SCD showed a similar genotype-specific association with the onset of menopause.
The onset of menopause is associated with a significant increase in the risk of cardiac events (dominated by recurrent episodes of syncope) in LQT2 women, suggesting that careful follow-up and continued long-term therapy are warranted in this population.
long-QT syndrome; women; estrogen; testosterone
Men and women with type 1 long QT syndrome (LQT1) exhibit time-dependent differences in the risk for cardiac events.
We hypothesized that sex-specific risk for LQT1 is related to the location and function of the disease-causing mutation in the KCNQ1 gene.
The risk for life-threatening cardiac events (comprising aborted cardiac arrest [ACA] or sudden cardiac death [SCD]) from birth through age 40 years was assessed among 1051 individuals with LQT1 (450 men and 601 women) by the location and function of the LQT1-causing mutation (prespecified as mutations in the intracellular domains linking the membrane-spanning segments [ie, S2–S3 and S4–S5 cytoplasmic loops] involved in adrenergic channel regulation vs other mutations).
Multivariate analysis showed that during childhood (age group: 0–13 years) men had >2-fold (P < .003) increased risk for ACA/SCD than did women, whereas after the onset of adolescence the risk for ACA/SCD was similar between men and women (hazard ratio = 0.89 [P = .64]). The presence of cytoplasmic-loop mutations was associated with a 2.7-fold (P < .001) increased risk for ACA/SCD among women, but it did not affect the risk among men (hazard ratio 1.37; P = .26). Time-dependent syncope was associated with a more pronounced risk-increase among men than among women (hazard ratio 4.73 [P < .001] and 2.43 [P = .02], respectively), whereas a prolonged corrected QT interval (≥500 ms) was associated with a higher risk among women than among men.
Our findings suggest that the combined assessment of clinical and mutation location/functional data can be used to identify sex-specific risk factors for life-threatening events for patients with LQT1.
Cytoplasmic-loop mutations; Sex; Long QT syndrome; Sudden cardiac death
Information is limited regarding the knowledge and attitudes of physicians typically involved in the referral of patients for implantable cardioverter defibrillator (ICD) implantation.
We conducted a survey of primary care physicians and cardiologists at the University of Rochester Medical Center and the Unity Health System Rochester, NY from December 2008 to February 2009. The survey collected information regarding knowledge and attitudes of physicians towards ICD therapy.
Of the 332 surveys distributed, 110 (33%) were returned. Over-all 94 (87%) physicians reported referring patients for ICD implantation. Eighteen (17%) physicians reported unawareness of guidelines for ICD use. Sixty-four (59%) physicians recommended ICD in patients with ischemic cardiomyopathy and left ventricular ejection fraction (LVEF) ≤ 35%. Sixty-five (62%) physicians use ≤ 35% as LVEF criteria for ICD referral in patients with non-ischemic cardiomyopathy. Cardiologists were more familiar than primary care physicians with LVEF criteria for implantation of ICD in patients with ischemic and non-ischemic cardiomyopathy (p value 0.005 and 0.002 respectively). Twenty-nine (27%) participants were unsure regarding benefits of ICDs in eligible women and Blacks. Eighty two (76%) physicians believed that an ICD could benefit patients ≥70 years whereas only 53 (49%) indicated that an ICD would benefit patients ≥ 80 years of age. A lack of familiarity with current clinical guidelines regarding ICD implantation exists. Primary care physicians are less aware of clinical guidelines than are cardiologists. This finding highlights the need to improve the dissemination of guidelines to primary care physicians in an effort to improve ICD utilization.
Implantable cardioverter defibrillator; Physician’s Knowledge; Gender and Racial Disparities
Type-1 long-QT syndrome (LQTS) is caused by loss-of-function mutations in the KCNQ1-encoded IKs cardiac potassium channel. We evaluated the effect of location, coding type, and biophysical function of KCNQ1 mutations on the clinical phenotype of this disorder.
Methods and Results
We investigated the clinical course in 600 patients with 77 different KCNQ1 mutations in 101 proband-identified families derived from the US portion of the International LQTS Registry (n=425), the Netherlands’ LQTS Registry (n=93), and the Japanese LQTS Registry (n=82). The Cox proportional hazards survivorship model was used to evaluate the independent contribution of clinical and genetic factors to the first occurrence of time-dependent cardiac events from birth through age 40 years. The clinical characteristics, distribution of mutations, and overall outcome event rates were similar in patients enrolled from the 3 geographic regions. Biophysical function of the mutations was categorized according to dominant-negative (>50%) or haploinsufficiency (≤50%) reduction in cardiac repolarizing IKs potassium channel current. Patients with transmembrane versus C-terminus mutations (hazard ratio, 2.06; P<0.001) and those with mutations having dominant-negative versus haploinsufficiency ion channel effects (hazard ratio, 2.26; P<0.001) were at increased risk for cardiac events, and these genetic risks were independent of traditional clinical risk factors.
This genotype–phenotype study indicates that in type-1 LQTS, mutations located in the transmembrane portion of the ion channel protein and the degree of ion channel dysfunction caused by the mutations are important independent risk factors influencing the clinical course of this disorder.
electrocardiography; genetics; long-QT syndrome
This study was designed to assess the clinical course and to identify risk factors for life-threatening events in patients with long-QT syndrome (LQTS) with normal corrected QT (QTc) intervals.
Current data regarding the outcome of patients with concealed LQTS are limited.
Clinical and genetic risk factors for aborted cardiac arrest (ACA) or sudden cardiac death (SCD) from birth through age 40 years were examined in 3,386 genotyped subjects from 7 multinational LQTS registries, categorized as LQTS with normal-range QTc (≤440 ms [n = 469]), LQTS with prolonged QTc interval (>440 ms [n = 1,392]), and unaffected family members (genotyped negative with ≤440 ms [n = 1,525]).
The cumulative probability of ACA or SCD in patients with LQTS with normal-range QTc intervals (4%) was significantly lower than in those with prolonged QTc intervals (15%) (p < 0.001) but higher than in unaffected family members (0.4%) (p < 0.001). Risk factors ACA or SCD in patients with normal-range QTc intervals included mutation characteristics (transmembrane-missense vs. nontransmembrane or nonmissense mutations: hazard ratio: 6.32; p = 0.006) and the LQTS genotypes (LQTS type 1:LQTS type 2, hazard ratio: 9.88; p = 0.03; LQTS type 3:LQTS type 2, hazard ratio: 8.04; p = 0.07), whereas clinical factors, including sex and QTc duration, were associated with a significant increase in the risk for ACA or SCD only in patients with prolonged QTc intervals (female age >13 years, hazard ratio: 1.90; p = 0.002; QTc duration, 8% risk increase per 10-ms increment; p = 0.002).
Genotype-confirmed patients with concealed LQTS make up about 25% of the at-risk LQTS population. Genetic data, including information regarding mutation characteristics and the LQTS genotype, identify increased risk for ACA or SCD in this overall lower risk LQTS subgroup.
corrected QT interval; long-QT syndrome; sudden cardiac death
Genotype-phenotype investigations have revealed significantly larger risk for cardiac events in patients with type 1 long-QT syndrome (LQT-1), particularly in adult females, with missense mutation in the cytoplasmic loop (C-loop) regions of the α subunit of the KCNQ1 gene associated with an impaired ion channel activation by adrenergic stimulus. We hypothesize that the impaired response to increases in heart rate leads to abnormal QT-RR dynamic profiles and is responsible for the increased cardiac risk for these patients.
Methods and Results
We measured the QT-RR slope in 24-hour Holter ECGs from LQT-1 patients with the mutations associated with impaired adrenergic stimulus (C-loop, n=18) and compared to LQT-1 patients with other mutations (non–C-loop, n=48), and to a healthy control group (n=195). The diurnal QT-RR slope was less steep in C-loop mutation patients (0.10±0.05) than in the ECGs from non–C-loop mutation patients (0.17±0.09, P=0.002). For female patients, slower heart rates were associated with prolonged QT and increased QT-RR slope. Male patients with C-loop mutations showed an impaired repolarization for shorter range of heart rates than in females, which is consistent with gender differences in triggers for events in this syndrome.
Our observations suggest that the C-loop LQT-1 patients have specific impaired adrenergic regulation of the ventricular repolarization. This response to heart rate increases may be useful in identification of high-risk patients with inherited prolonged QT and may help select an optimal antiarrhythmic therapeutic strategy. (J Am Heart Assoc. 2012;1:e000570 doi: 10.1161/JAHA.112.000570.)
electrocardiogram; KCNQ1; long-QT syndrome; QT interval; QT-RR dynamicity
We aimed to identify risk factors for recurrent syncope in children and adolescents with congenital long QT syndrome (LQTS).
Data regarding risk assessment in LQTS after the occurrence of first syncope are limited.
The Prentice-Williams-Peterson conditional gap time model was utilized to identify risk factors for recurrent syncope from birth through age 20 years among 1648 patients from the International LQTS Registry.
Multivariate analysis demonstrated that QTc duration (≥500 msec) was a significant predictor of a first syncope (HR=2.16), whereas QTc effect was attenuated when the endpoints of second-, third-, and fourth- syncope were evaluated (HR = 1.29, 0.99, 0.90, respectively; p<0.001 for the null hypothesis that all four HRs are identical). A genotype-specific sub-analysis showed that during childhood (0–12 years) LQT1 males had the highest rate of first syncope (p=0.001), but exhibited similar rates of subsequent events as other genotype-gender subsets (p=0.63). In contrast, in the age-range of 13–20 years, LQT2 females experienced the highest rate of both first and subsequent events (p<0.001 and p=0.01, respectively). Patients who experienced ≥1 episodes of syncope had a 6–12-fold (p<0.001 for all) increase in the risk of subsequent fatal/near-fatal events independently of QTc. Beta-blocker therapy was associated with a significant reduction in the risk of recurrent syncope and subsequent fatal/near-fatal events.
Children and adolescents who present following an episode of syncope should be considered to be at a high a risk for the development of subsequent syncopal episodes and fatal/near-fatal events regardless of QTc duration.
long qt syndrome; corrected QT interval; reccurrent events; syncope; sudden cardiac death
Data regarding possible ion channel mechanisms that predispose to ventricular tachyarrhythmias in patients with phenotype-negative long-QT syndrome (LQTS) are limited.
Methods and Results
We carried out cellular expression studies for the S349W mutation in the KCNQ1 channel, which was identified in 15 patients from the International LQTS Registry who experienced a high rate of cardiac events despite lack of significant QTc prolongation. The clinical outcome of S349W mutation carriers was compared with that of QTc-matched carriers of haploinsufficient missense (n=30) and nonsense (n=45) KCNQ1 mutations. The channels containing the mutant S349W subunit showed a mild reduction in current (<50%), in the haploinsuficient range, with an increase in maximal conductance compared with wild type channels. In contrast, expression of the S349W mutant subunit produced a pronounced effect on both the voltage dependence of activation and the time constant of activation, while haploinsuficient channels showed no effect on either parameter. The cumulative probability of cardiac events from birth through age 20 years was significantly higher among S349W mutation carriers (58%) as compared with carriers of QTc-matched haploinsufficent missense- (21% p=0.004) and nonsense- (25%; p=0.01) mutations.
The S349W mutation in the KCNQ1 potassium channel exerts a relatively mild effect on the ion channel current, whereas an increase in conductance compensates for impaired voltage activation of the channel. The changes observed in voltage activation of the channel may underlie the mechanisms predisposing to arrhythmic risk among LQTS patients with a normal-range QTc.
long-QT syndrome; corrected QT interval; potassium ion channel current; ventricular tachycardia; sudden death
Arrhythmogenic right ventricular cardiomyopathy/dysplasia (ARVC/D) is an inherited disease causing structural and functional abnormalities of the right ventricle (RV). The presence of late potentials as assessed by the signal averaged electrocardiogram (SAECG) is a minor Task Force criterion.
The purpose of this study was to examine the diagnostic and clinical value of the SAECG in a large population of genotyped ARVC/D probands.
We compared the SAECGs of 87 ARVC/D probands (age 37 ± 13 years, 47 males) diagnosed as affected or borderline by Task Force criteria without using the SAECG criterion with 103 control subjects. The association of SAECG abnormalities was also correlated with clinical presentation; surface ECG; VT inducibility at electrophysiologic testing; ICD therapy for VT; and RV abnormalities as assessed by cardiac magnetic resonance imaging (cMRI).
When compared with controls, all 3 components of the SAECG were highly associated with the diagnosis of ARVC/D (p<0.001). These include the filtered QRS duration (fQRSD) (97.8 ± 8.7 msec vs. 119.6 ± 23.8 msec), low amplitude signal (LAS) (24.4 ± 9.2 msec vs. 46.2 ± 23.7 msec) and root mean square amplitude of the last 40 msec of late potentials (RMS-40) (50.4 ± 26.9 µV vs. 27.9 ± 36.3 µV). The sensitivity of using SAECG for diagnosis of ARVC/D was increased from 47% using the established 2 of 3 criteria (i.e. late potentials) to 69% by using a modified criterion of any 1 of the 3 criteria, while maintaining a high specificity of 95%. Abnormal SAECG as defined by this modified criteria was associated with a dilated RV volume and decreased RV ejection fraction detected by cMRI (p<0.05). SAECG abnormalities did not vary with clinical presentation or reliably predict spontaneous or inducible VT, and had limited correlation with ECG findings.
Using 1 of 3 SAECG criteria contributed to increased sensitivity and specificity for the diagnosis of ARVC/D. This finding is incorporated in the recent modification of the Task Force criteria.
Arrhythmogenic right ventricular cardiomyopathy/dysplasia (ARVC/D); signal-averaged electrocardiogram (SAECG)
Thorough QT (TQT) studies are designed to evaluate potential effect of a novel drug on the ventricular repolarization process of the heart using QTc prolongation as a surrogate marker for torsades de pointes. The current process to measure the QT intervals from the thousands of electrocardiograms is lengthy and expensive. In this study, we propose a validation of a highly-automatic QT interval measurement (HA-QT) method. We applied a HA-QT measurement method to the data from seven TQT studies. We investigated both the placebo and baseline-adjusted QTc interval prolongation induced by moxifloxacin (positive control drug) at the time of expected peak concentration. The comparative analysis evaluated the time course of moxifloxacin-induced QTc prolongation in one study as well. The absolute HA-QT data were longer than the FDA-approved QTc data. This trend was not different between ECGs from the moxifloxacin and placebo arms: 9.6±24msec on drug and 9.8±25msec on placebo. The difference between methods vanished when comparing the placebo-baseline-adjusted QTc prolongation (1.4±2.8msec, p=0.4). The differences in precision between the HA-QT and the FDA-approved measurements were not statistically different from zero: 0.1±0.1msec (p=0.7). Also, the time course of the moxifloxacin-induced QTc prolongation adjusted for placebo was not statistically different between measurements methods.
thorough QT study; drug cardiotoxicity; moxifloxacin; QT interval; electrocardiogram; drug safety
Cardiac events in long-QT syndrome type-2 (LQT2) patients are predominately associated with sudden arousal. However, exercise-induced events also occur in this population.
We hypothesized that risk factors show a trigger-specific association with cardiac events in LQT2 patients.
The study population comprised 634 genetically-confirmed LQT2 patients from the US portion of the International LQTS Registry. Multivariate Cox proportional hazards regression analysis was used to determine the independent contribution of clinical and genetic risk factors to the first occurrence of trigger-specific cardiac events, categorized as arousal, exercise-induced, and non-arousal/non-exercise, from birth through age 40 years.
Study patients experienced 204 cardiac events during follow-up, of which 44% were associated with arousal-triggers, 13% with exercise activity, and 43% with non-exercise/non-arousal triggers. Risk factors for arousal triggered cardiac events included gender (female:male >13 years: HR=9.10 [p<0.001]), and the presence of pore-loop mutations (HR=2.19 [p=0.009]). In contrast, non pore-loop transmembrane mutations were the predominant risk factor for exercise-triggered events (HR=6.84 [p<0.001]), whereas gender was not a significant risk factor for this end point. Non-exercise/non-arousal events were associated with heterogeneous causes. Risk factors for this end point included gender, mutation-location and type, and a prolonged QTc (≥500 msec) Beta-blocker therapy was associated with a pronounced reduction in the risk of exercise-triggered events (HR=0.29 [p<0.01]), but had a non-significant effect on the risk of arousal- and non-exercise/non-arousal events.
Our findings suggest that management of patients with the LQT2 genotype should employ a trigger-specific approach to risk-assessment and medical therapy.
long-QT syndrome; ion channel mutations; sudden cardiac death; risk factors; beta-blockers
T-wave alternans (TWA), a harbinger of sudden cardiac death, associates to a broad variety of pathologies. In a previous study, we observed the presence of unstable and low-amplitude TWA also in healthy subjects, and considered it as “physiological TWA.” The possible existence of different TWA characteristics between males and female is investigated in the present work.
Resting ECG recordings from 142 control healthy subjects, 77 males and 65 females, were submitted to our adaptive match filter (AMF) based method for TWA detection and characterization in terms of duration, amplitude, and their product. The 99.5th percentile of these parameters distributions over the entire control population and over the male and female subgroups, were used to define thresholds which delimit a gender-independent and male- and female-related TWA normality regions, respectively, out of which abnormal TWA cases (TWA+) are expected to fall. Clinical usefulness of these regions was tested using a population of 151 coronary artery disease (CAD) patients, divided into 128 males and 23 females.
In our control-female population, TWA duration was significantly longer than in control-male population (65 ± 13 beat vs 52 ± 14 beat; P < 10−6). Our gender-related normality regions allowed identification of 36 (23.8%) TWA+ cases among the CAD patients, 17 more than those obtained from a gender-independent region. All these 17 patients were CAD males with over-threshold TWA duration.
TWA is a gender-related phenomenon. Definition of gender-related TWA normality regions improves identification of patients at increased TWA stability (i.e., prolonged TWA duration) and, thus, at increased risk of arrhythmic events.
repolarization variability; sudden cardiac death; ECG signal processing
To investigate roles of inflammation and a cholesteryl ester transfer protein (CETP) polymorphism potentially related to recent findings demonstrating coronary risk with increasing HDL cholesterol (HDL-C).
Methods and Results
A novel graphical exploratory data analysis tool allowed examination of coronary risk in postinfarction patients relating to HDL-C and C-reactive protein (CRP). Results demonstrated a high-risk subgroup defined by high HDL-C and CRP exhibiting larger HDL particles and lower lipoprotein-associated phospholipaseA2 (Lp-PLA2) levels than lower-risk patients. Subgroup CETP-associated risk was probed using a functional CETP polymorphism (TaqIB, rs708272). Multivariable modeling revealed in the high-risk subgroup greater risk for B2 allele-carriers (less CETP activity) versus B1 homozygotes (hazard ratio 2.41, 95% CI 1.04-5.60, p=0.041). Within the high-risk subgroup, B2 allele-carriers had higher serum amyloid A levels than B1 homozygotes. Evidence is also presented demonstrating CETP genotypic differences in HDL subfraction distributions regarding nonHDL-C and Lp-PLA2 potentially relating to impaired HDL remodeling.
Postinfarction patients with high HDL-C and CRP levels demonstrate increased risk for recurrent events. Future studies should aim at characterizing altered HDL particles from such patients and elucidating mechanistic details related to inflammation and HDL particle remodeling. Such patients should be considered in drug trials involving raising HDL-C.
Atherosclerosis; cardiovascular diseases; inflammation; cholesteryl ester transfer protein; TaqIB
The 2 predominant etiologies of right ventricular tachycardia (VT) are arrhythmogenic right ventricular cardiomyopathy (ARVC) and idiopathic VT arising from the right ventricular outflow tract (RVOT). Both of these arrhythmias can be adrenergically mediated and may be difficult to distinguish clinically. A minor criterion for the diagnosis of ARVC is T wave inversion (TWI) in the right precordial leads during sinus rhythm. However, there have been reports of precordial TWI identified in patients with RVOT tachycardia. The purpose of this study was to determine whether patterns of precordial TWI could differentiate between the two groups. We evaluated a multicenter registry of 229 patients with VT of right ventricular origin. After appropriate exclusions (n=29), 79 patients (58% M, 40±14y) had ARVC, and 121 patients (41% M, 48±14y) had RVOT tachycardia. During sinus rhythm, 37/79 (47%) patients with ARVC and 5/121 (4%) patients with RVOT tachycardia had T-wave inversion in leads V1-V3. For the diagnosis of ARVC, TWI in leads V1-V3 had a sensitivity of 47% and a specificity of 96%. In conclusion, in patients with VT of RV origin, the presence of TWI in electrocardiogram leads V1-V3 supports the diagnosis of ARVC.
ventricular tachycardia; arrhythmogenic right ventricular cardiomyopathy; ventricular outflow tract tachycardia; electrocardiography
In 1994, an International Task Force proposed criteria for the clinical diagnosis of ARVC/D which facilitated recognition and interpretation of the frequently non-specific clinical features of ARVC/D. This enabled confirmatory clinical diagnosis in index cases through exclusion of phenocopies, and provided a standard upon which clinical research and genetic studies could be based. Structural, histological, electrocardiographic, arrhythmic, and familial features of the disease were incorporated into the criteria, subdivided into major and minor according to the specificity of their association with ARVC/D. At that time, clinical experience with ARVC/D was dominated by symptomatic index cases and sudden cardiac death victims: the overt and/or severe end of the disease spectrum. Consequently, the 1994 criteria were highly specific but lacked sensitivity for early and familial disease.
Methods and Results
Revision of the diagnostic criteria provides guidance on the role of emerging diagnostic modalities and advances in the genetics of ARVC/D. The criteria have been modified to incorporate new knowledge and technology to improve diagnostic sensitivity, but with the important requisite of maintaining diagnostic specificity. The approach classifying structural, histological, electrocardiographic, arrhythmic, and genetic features of the disease as major and minor criteria has been maintained. In this modification of the Task Force Criteria, quantitative criteria are proposed and abnormalities are defined based on comparison with normal subject data.
The diagnosis of ARVC/D based on modification of the original Task Force criteria is a working framework to improve the diagnosis and management of this condition.
cardiomyopathy; diagnosis; echocardiography; electrocardiography; magnetic resonance imaging
In 1994, an International Task Force proposed criteria for the clinical diagnosis of arrhythmogenic right ventricular cardiomyopathy/dysplasia (ARVC/D) that facilitated recognition and interpretation of the frequently nonspecific clinical features of ARVC/D. This enabled confirmatory clinical diagnosis in index cases through exclusion of phenocopies and provided a standard on which clinical research and genetic studies could be based. Structural, histological, electrocardiographic, arrhythmic, and familial features of the disease were incorporated into the criteria, subdivided into major and minor categories according to the specificity of their association with ARVC/D. At that time, clinical experience with ARVC/D was dominated by symptomatic index cases and sudden cardiac death victims–the overt or severe end of the disease spectrum. Consequently, the 1994 criteria were highly specific but lacked sensitivity for early and familial disease.
Methods and Results
Revision of the diagnostic criteria provides guidance on the role of emerging diagnostic modalities and advances in the genetics of ARVC/D. The criteria have been modified to incorporate new knowledge and technology to improve diagnostic sensitivity, but with the important requisite of maintaining diagnostic specificity. The approach of classifying structural, histological, electrocardiographic, arrhythmic, and genetic features of the disease as major and minor criteria has been maintained. In this modification of the Task Force criteria, quantitative criteria are proposed and abnormalities are defined on the basis of comparison with normal subject data.
The present modifications of the Task Force Criteria represent a working framework to improve the diagnosis and management of this condition.
Clinical Trial Registration
clinicaltrials.gov Identifier: NCT00024505.
Arrhythmias, cardiac; Arrhythmogenic right ventricular cardiomyopathy/dysplasia; Death, sudden, cardiac; Diagnosis; Echocardiography; Electrocardiography; Magnetic resonance imaging