Electrogram fractionation and atrial fibrosis are both thought to be pathophysiological hallmarks of evolving persistence of atrial fibrillation (AF), but recent studies in humans have shown that they do not colocalize. The interrelationship and relative roles of fractionation and fibrotic change in AF persistence therefore remain unclear.
The aim of the study was to examine the hypothesis that electrogram fractionation with increasing persistence of AF results from localized conduction slowing or block due to changes in atrial connexin distribution in the absence of fibrotic change.
Of 12 goats, atrial burst pacemakers maintained AF in 9 goats for up to 3 consecutive 4-week periods. After each 4-week period, 3 goats underwent epicardial mapping studies of the right atrium and examination of the atrial myocardium for immunodetection of connexins 43 and 40 (Cx43 and Cx40) and quantification of connective tissue.
Despite refractoriness returning to normal in between each 4-week period of AF, there was a cumulative increase in the prevalence of fractionated atrial electrograms during both atrial pacing (control and 1, 2, and 3 months period of AF 0.3%, 1.3% ± 1.5%, 10.6% ± 2%, and 17% ± 5%, respectively; analysis of variance, P < .05) and AF (0.3% ± 0.1%, 2.3% ± 1.2%, 14% ± 2%, and 23% ± 3%; P < .05) caused by colocalized areas of conduction block during both pacing (local conduction velocity <10 cm/s: 0.1% ± 0.1%, 0.3% ± 0.6%, 6.5% ± 3%, and 6.9% ± 4%; P < .05) and AF (1.5% ± 0.5%, 2.7% ± 1.1%, 10.1% ± 1.2%, and 13.6% ± 0.4%; P < .05), associated with an increase in the heterogeneity of Cx40 and lateralization of Cx43 (lateralization scores: 1.75 ± 0.89, 1.44 ± 0.31, 2.85 ± 0.96, and 2.94 ± 0.31; P < .02), but not associated with change in connective tissue content or net conduction velocity.
Electrogram fractionation with increasing persistence of AF results from slow localized conduction or block associated with changes in atrial connexin distribution in the absence of fibrotic change.
AERP, atrial effective refractory period; AF, atrial fibrillation; ANOVA, analysis of variance; CV, conduction velocity; Cx40, connexin 40; Cx43, connexin 43; MRI, magnetic resonance imaging; NPV, negative predictive value; PPV, positive predictive value; Atrial fibrillation; Fractionation; Connexin; Conduction
Studies from several laboratories have implicated intracellular Ca2+ dynamics in the modulation of electrical activity. We have reported that abnormal Ca2+ wave activity is the underlying cause of afterdepolarization-induced electrical activity in subendocardial Purkinje cells that survive in the 48-hour infarcted canine heart. These cells form the focus of arrhythmias at this time postcoronary artery occlusion.
We studied the effects of agonists and antagonists on the abnormal Ca2+ release activity of Purkinje cell aggregates dispersed from the subendocardium 48 hours postcoronary artery occlusion (IZPCs). Studies were completed using epifluorescent microscopy of Fluo-3 loaded Purkinje cells.
Similar to our previous report, highly frequent traveling micro Ca2+ transients(μCaiTs) and cell-wide Ca2+ waves were seen in IZPCs in the absence of any drug. Isoproterenol (ISO) increased μCaiTs and cell-wide Ca2+ waves in Purkinje cells dispersed from the normal heart (NZPCs). In IZPCs, ISO increased cell-wide wave frequency but had no effect on the already highly frequent micro Ca2+ wave transient activity, suggesting that ISO lowers the threshold of cell-wide generators responding to micro Ca2+ transients. Drugs that block inward sodium or calcium currents (verapamil, tetrodotoxin) had no effect on Ca2+ activity in Purkinje cells. Antagonists of intracellular Ca2+ release channels [ryanodine, JTV519(K201)] greatly suppressed spontaneous Ca2+ release events in IZPCs. 2APB, an agent that blocks IP3 receptors, greatly reduced the frequency of Ca2+events in IZPCs.
In arrhythmogenic Purkinje cells that survive in the infarcted heart, agents that block or inhibit intracellular Ca2+ release channel activity reduced Ca2+ waves and could be antiarrhythmic.
Purkinje; Action potentials; Ca2+ waves; Cai transients; Automaticity; Myocardial infarction
Complex fractionated atrial electrograms (CFAEs) may represent a phenomenon associated with sources of atrial fibrillation (AF) and are being used increasingly as targets of catheter ablation. However, current methods have limited efficacy for characterizing CFAEs important to substrate arrhythmogenicity and do not measure electrogram morphology.
The purpose of this study was to develop a methodology for quantifying the degree of morphologic heterogeneity in CFAE deflections, and to determine whether there are differences in this measurement between paroxysmal and persistent AF patients.
Two successive bipolar CFAEs of length 8.4 seconds each were acquired during AF from two sites each at the ostia of the four pulmonary veins (PVs) and from the anterior and posterior left atrial free wall in patients with paroxysmal AF (N =10) and long-standing persistent AF (N = 10). Extrinsic and intrinsic features of electrogram shape were used to characterize fractionation in CFAE sequences. The extrinsic parameters were the amplitude, upslope, downslope, and width of each deflection. The intrinsic parameter was the voltage profile as characterized by the sum of absolute values. These measurements were compared to the mean interval between CFAE deflections, a standard fractionation indicator.
The variability of intrinsic/extrinsic morphologic parameters was higher in paroxysmal than persistent AF at the left superior PV (P ≤.003), the posterior left atrial free wall, anterior left atrial free wall, left inferior PV, and right superior PV (P <.05 for most parameters), and the right inferior PV (not significant). Mean CFAE deflection intervals were longer at all locations in paroxysmal AF but were significant only at the left superior PV and posterior left atrial free wall (P <.05). Quantitative morphologic parameters were not well correlated with dominant frequency (r2 <0.32); thus, our new measures are robust to changes in activation rate.
A novel method for quantifying CFAEs, independent of activation rate, has been developed. The method demonstrates greater significance in the difference between CFAE morphology in paroxysmal and long-standing AF compared with mean interval between CFAE deflections. The differences identified suggest that CFAE morphology may evolve as AF persists.
Atrial fibrillation; Fractionation; Left atrium
Under conditions promoting early afterdepolarizations (EADs), ventricular tissue can become bi-excitable, that is, capable of wave propagation mediated by either the Na current (INa) or the L-type calcium current (ICa,L), raising the possibility that ICa,L-mediated reentry may contribute to polymorphic ventricular tachycardia (PVT) and torsades de pointes. ATP-sensitive K current (IKATP) activation suppresses EADs, but the effects on ICa,L-mediated reentry are unknown.
To investigate the effects of IKATP activation on ICa,L-mediated reentry.
We performed optical voltage mapping in cultured neonatal rat ventricular myocyte monolayers exposed to BayK8644 and isoproterenol. The effects of pharmacologically activating IKATP with pinacidil were analyzed.
In 13 monolayers with anatomic ICa,L-mediated reentry around a central obstacle, pinacidil (50 μM) converted ICa,L-mediated reentry to INa-mediated reentry. In 33 monolayers with functional ICa,L-mediated reentry (spiral waves), pinacidil terminated reentry in 17, converted reentry into more complex INa-mediated reentry resembling fibrillation in 12, and had no effect in 4. In simulated 2-dimensional bi-excitable tissue in which ICa,L- and INa-mediated wave fronts coexisted, slow IKATP activation (over minutes) reliably terminated rotors but rapid IKATP activation (over seconds) often converted ICa,L-mediated reentry to INa-mediated reentry resembling fibrillation.
IKATP activation can have proarrhythmic effects on EAD-mediated arrhythmias if ICa,L-mediated reentry is present.
Early afterdepolarizations; Reentry; Bi-excitability; Torsades de pointes; ATP-sensitive K channels; Pinacidil
We previously reported that induced Pluripotent Stem Cell-derived cardiomyocytes (iPSC-CM) manifest beat rate variability (BRV) resembling heart rate variability (HRV) in human sinoatrial node (SAN). We now hypothesized the BRV-HRV continuum originates in pacemaker cells.
To investigate whether cellular BRV is a source of HRV dynamics, we hypothesized three-levels of interaction among different cardiomyocyte entities: (1) single pacemaker cells, (2) networks of electrically coupled pacemaker cells and (3) in situ SAN.
We measured BRV/HRV properties in single pacemaker cells, iPSC-derived contracting embryoid bodies (EBs) and electrocardiograms from the same individual.
Pronounced BRV/HRV were present at all three levels. Coefficient of variance (COV) of inter-beat intervals (IBI) and Poincaré plot SD1 and SD2 in single cells were 20x > EBs (P<0.05) and in situ heart (the latter two were similar, P>0.05). We also compared BRV magnitude among single cells, small (~5-10 cells) and larger EBs (>10 cells): BRV indices progressively increased (P<0.05) as cell number decreased. Disrupting intracellular Ca2+ handling markedly augmented BRV magnitude, revealing a unique bi-modal firing pattern, suggesting intracellular mechanisms contribute to BRV/HRV and the fractal behavior of heart rhythm.
The decreased BRV magnitude in transitioning from single cell to EB suggests HRV of hearts in situ originates from summation and integration of multiple cell-based oscillators. Hence, complex interactions among multiple pacemaker cells and intracellular Ca2+ handling determine HRV in humans and isolated cardiomyocyte networks.
Electrophysiology; Heart rate; Induced Pluripotent Stem Cells; Heart Rate Variability; Cardiac Myocytes
Ablation has become an important option for treatment of ventricular tachycardia (VT). The influence of procedure duration on outcomes remains unexamined.
The purpose of this study was to determine the influence of procedure duration on outcomes and complications over an 8-year period
Patients referred for scar-mediated VT ablation from 2004 to 2011 were retrospectively analyzed. Procedure duration was defined as the time from the insertion of catheters through the femoral vein to the time of their withdrawal. Procedure duration was analyzed in relationship with baseline and intraoperative covariates, acute procedural outcomes, complications, and 6-month clinical outcomes.
One hundred forty-eight patients underwent VT ablation with mean procedure duration of 5.7 ± 1.8 hours. VT recurrence and survival at 6 months were 46% and 82%, respectively, and were not associated with procedure duration. Hospital mortality increased with intraoperative intraaortic balloon pump insertion (adjusted odds ratio [OR] 13.7, 95% confidence interval [CI] 2.35–79.94, P = .004) and was improved with successful ablation of the clinical VT as a procedural end-point (adjusted OR 0.13, 95% Cl 0.03–0.54, P = .005). The association between procedure duration and hospital mortality remained after adjusting for significant baseline variables (adjusted OR 1.75, 95% CI 1.14–2.68, P = .0098) and intraoperative variables (adjusted OR 1.6, 95% CI 1.12–2.29, P = .0104).
Hospital mortality was significantly increased by unsuccessful clinical VT ablation as a procedural end-point and intraoperative intraaortic balloon pump insertion. However, after adjusting for significant baseline and intraoperative covariates, procedure duration still was associated with increased hospital mortality. Procedure duration had no impact on VT recurrence and survival at 6 months.
Ventricular tachycardia; Ventricular tachycardia ablation; Procedure duration; Ventricular tachycardia ablation efficacy; Ventricular tachycardia recurrence; Hospital mortality
The measurement of late gadolinium enhanced MRI (LGE-MRI) intensity in arbitrary units (au), limits the objectivity of thresholds for focal scar detection and inter-patient comparisons of scar burden.
We sought to develop and validate a normalized measure, the image intensity ratio (IIR), for assessment of left atrial (LA) scar on LGE-MRI.
ECG- and respiratory-gated 1.5 Tesla LGE-MRI was performed in 75 patients (75% male, 62±8 years) prior to atrial fibrillation (AF) ablation. The local IIR was defined as LA myocardial signal intensity for each of 20 sectors on contiguous axial image planes divided by the mean LA blood pool image intensity. Intra-cardiac point-by-point sampled electro-anatomical map (EAM) points were co-registered with corresponding image sectors.
The average bipolar voltage for all 8,153 EAM points was 0.9±1.1 mV. In a mixed effects model accounting for within patient clustering, and adjusting for age, LA volume and mass, body mass index, gender, CHA2DS2-VASc score, AF type, history of previous ablations, and contrast delay time, each unit increase in local IIR was associated with 91.3% decrease in bipolar LA voltage (P<0.001). Local IIR thresholds of >0.97 and >1.61 corresponded to bipolar voltage <0.5 mV and <0.1 mV, respectively.
Normalization of LGE-MRI intensity by the mean blood pool intensity results in a metric that is closely associated with intra-cardiac voltage as a surrogate of atrial fibrosis.
atrial fibrillation; scar; late-gadolinium enhanced magnetic resonance imaging; electroanatomic mapping
Rare variants in candidate atrial fibrillation (AF) genes have been associated with AF in small kindreds. The extent to which such polymorphisms contribute to AF is unknown.
The purpose of this study was to determine the spectrum and prevalence of rare amino acid coding (AAC) variants in candidate AF genes in a large cohort of unrelated lone AF probands.
We resequenced 45 candidate genes in 303 European American (EA) lone AF probands (186 lone AF probands screened for each gene on average [range 89–303], 63 screened for all) identified in the Vanderbilt AF Registry (2002–2012). Variants detected were screened against 4300 EAs from the Exome Sequencing Project (ESP) to identify very rare (minor allele frequency ≤ 0.04%) AAC variants and these were tested for AF co-segregation in affected family members where possible.
Median age at AF onset was 46.0 years [interquartile range 33.0–54.0], and 35.6% had a family history of AF. Overall, 63 very rare AAC variants were identified in 60 of 303 lone AF probands, and 10 of 19 (52.6%) had evidence of co-segregation with AF. Among the 63 lone AF probands who had 45 genes screened, the very rare variant burden was 22%. Compared with the 4300 EA ESP, the proportion of lone AF probands with a very rare AAC variant in CASQ2 and NKX2-5 was increased 3–5-fold (P < .05).
No very rare AAC variants were identified in ~80% of lone AF probands. Potential reasons for the lack of very rare AAC variants include a complex pattern of inheritance, variants in as yet unidentified AF genes or in noncoding regions, and environmental factors.
Atrial fibrillation arrhythmia; Candidate genes; Family study; Genetic variation; Genetic epidemiology; Proarrhythmia; Rare variants
Radiofrequency (RF) ablation to treat atrial arrhythmia is limited by an inability to reliably assess lesion durability and transmurality.
Determine feasibility of photoacoustic characterization of myocardial ablation lesions in vitro. In this study, we investigate the feasibility of combined ultrasound (US) and spectroscopic photoacoustic (sPA) imaging to visualize RF ablation lesions in 3-D based on unique differences in the optical absorption spectra between normal and ablated myocardial tissue.
Tissue samples were excised from the ventricles of fresh porcine hearts. Lesions were generated using an RF catheter ablation system using 20 - 30 W of power applied for 40 - 60 s. Ablated samples were imaged in the NIR regime (740-780 nm) using a combined PA/US imaging system. Measured PA spectra were correlated to the absorption spectra of deoxy-hemoglobin and ablated tissue to produce a tissue characterization map (TCM) identifying 3-D lesion location and extent. Tissue samples were stained and photographed for gross pathology. TCM and gross pathology images were co-registered to assess TCM accuracy.
The TCM reliably characterized ablated and non-ablated tissue up to depths of 3 mm. The TCM also assessed lesion position and extent with sub-millimeter accuracy in multiple dimensions. Segmented TCMs achieved greater than 69% agreement with gross pathology.
These results suggest that sPA imaging has the potential to accurately assess RF ablation lesion size and position with sub-millimeter precision and may be well suited to guide trans-catheter RF atrial ablation in clinical practice.
Ablation; Atrial fibrillation; Radiofrequency; Imaging; Photoacoustic; Tissue characterization
Evidence from a canine experimental acute myocardial infarction (MI) model shows that until the seventh week after MI the relationship between stellate ganglionic nerve and vagal nerve activities (SGNA/VNA) progressively increases.
We evaluated how autonomic nervous system activity influences temporal myocardial repolarization dispersion at this period.
We analyzed autonomic nerve activity as well as QT and RR variability from recordings previously obtained in 9 dogs. From a total 48 short-term electrocardiographic segments, 24 recorded before and 24 seven weeks after experimentally-induced MI, we obtained three indices of temporal myocardial repolarization dispersion: QTe (from q wave T to wave end), QTp (from q wave to T wave peak) and Te (from T wave peak to T wave end) variability index (QTeVI, QTpVI, TeVI). We also performed a heart rate variability power spectral analysis on the same segments.
After MI, all the QT variables increased QTeVI (median [interquartile range]) (from - 1.76[0.82] to −1.32[0.68]), QTeVI (from −1.90[1.01] to −1.45[0.78]) and TeVI (from −0.72[0.67] to −0.22[1.00]), whereas all RR spectral indexes decreased (p<0.001 for all). Distinct circadian rhythms in QTeVI (p<0.05,) QTpVI (p<0.001) and TeVI (p<0.05) appeared after MI with circadian variations resembling that of SGNA/VNA. The morning QTpVI and TeVI acrophases approached the SGNA/VNA acrophase. Conversely, the evening QTeVI acrophase coincided with another SGNA/VNA peak. After MI, regression analysis detected a positive relationship between SGNA/VNA and TeVI (R2: 0.077; β: 0.278; p< 0.001).
Temporal myocardial repolarization dispersion shows a circadian variation after MI reaching its peak at a time when sympathetic is highest and vagal activity lowest.
Voltage-sensitive dyes are important tools for mapping electrical activity in the heart. However, little is known about the effects of voltage-sensitive dyes on cardiac electrophysiology.
To test the hypothesis that the voltage-sensitive dye di-4-ANEPPS modulates cardiac impulse propagation.
Electrical and optical mapping experiments were performed in isolated Langendorff perfused guinea pig hearts. The effect of di-4-ANEPPS on conduction velocity and anisotropy of propagation was quantified. HeLa cells expressing connexin 43 were used to evaluate the effect of di-4-ANEPPS on gap junctional conductance.
In electrical mapping experiments, di-4-ANEPPS (7.5 μM) was found to decrease both longitudinal and transverse conduction velocities significantly compared with control. No change in the anisotropy of propagation was observed. Similar results were obtained in optical mapping experiments. In these experiments, the effect of di-4-ANEPPS was dose dependent. di-4-ANEPPS had no detectable effect on connexin 43–mediated gap junctional conductance in transfected HeLa cells.
Our results demonstrate that the voltage-sensitive dye di-4-ANEPPS directly and dose-dependently modulates cardiac impulse propagation. The effect is not likely mediated by connexin 43 inhibition. Our results highlight an important caveat that should be taken into account when interpreting data obtained using di-4-ANEPPS in cardiac preparations.
Voltage-sensitive dye; di-4-ANEPPS; Guinea pig; Conduction; Electrical mapping; Optical mapping
Concern exists regarding the potential electromagnetic interaction between pacemakers, implantable cardioverter-defibrillators (ICDs) and digital music players (DMPs). A preliminary study reported interference in 50% of patients whose devices were interrogated near Apple iPods.
Given the high prevalence of DMP use among young patients, we sought to define the nature of interference from iPods and evaluate other DMPs.
Four DMPs (Apple Nano, Apple Video, SanDisk Sansa and Microsoft Zune) were evaluated against pacemakers and ICDs (PM/ICD). Along with continuous monitoring, we recorded a baseline ECG strip, sensing parameters and lead impedance at baseline and for each device.
Among 51 patients evaluated (age 6 to 60 years, median 22), there was no interference with intrinsic device function. Interference with the programmer occurred in 41% of the patients. All four DMPs caused programmer interference, including disabled communication between the PM/ICD and programmer, noise in the ECG channel, and lost marker channel indicators. Sensing parameters and lead impedance exhibited no more than baseline variability. When the DMPs were removed six inches, there were no further programmer telemetry interactions.
Contrary to a prior report, we did not identify any evidence for electromagnetic interference between a selection of DMPs and intrinsic function of PM/ICDs. The DMPs did sometimes interfere with device-programmer communication, but not in a way that compromised device function. Therefore, we recommend that DMPs not be used during device interrogation, but suggest that there is reassuring counterevidence to mitigate the current high level of concern for interactions between DMPs and implantable cardiac rhythm devices.
pacemaker; implantable cardioverter defibrillator; electromagnetic interference; pediatrics; congenital heart disease
KCNJ2 mutations are associated with a variety of inherited arrhythmia syndromes including CPVT3.
Detailed cellular and mechanistic characterization of the clinically recognized KCNJ2 mutation R67Q.
Kir2.1 current density was measured using the whole-cell voltage clamp technique from COS-1 cells transiently transfected with WT-Kir2.1 and/or R67Q-Kir2.1. Catecholamine activity was simulated with PKA stimulating cocktail exposure. Phosphorylation deficient mutants, S425N-Kir2.1 and S425N-Kir2.1/R67Q-S425N-Kir2.1, were used in a separate set of experiments. HA- or Myc-Tag-WT-Kir2.1 or HA-Tag-R67Q-Kir2.1 were used for confocal imaging.
A 33 year old presented with a CPVT-like clinical phenotype and was found to have KCNJ2 missense mutation R67Q. Treatment with nadolol and flecainide resulted in complete suppression of arrhythmias and symptom resolution.
Under baseline conditions, R67Q-Kir2.1 expressed alone did not produce IK1 while cells co-expressing WT-Kir2.1 and R67Q-Kir2.1 showed rectification index (RI) similar to WT-Kir2.1. After PKA stimulation, R67Q-Kir2.1/WT-Kir2.1 failed to increase peak outward current density; WT-Kir2.1 increased 46% (n=5) while R67Q-Kir2.1/WT-Kir2.1 decreased 6% (n=6), p=0.002. Rectification properties in R67Q-Kir2.1/WT-Kir2.1 demonstrated sensitivity to calcium with decreased RI in high-calcium pipette solution (RI 20.3 ± 4.1%) compared to low-calcium (RI 36.5 ± 5.7%) (p< 0.05). Immunostaining of WT-Kir2.1 and R67Q-Kir2.1 individually and together showed a normal membrane expression pattern and co-localization by Pearson’s correlation coefficient.
R67Q-Kir2.1 is associated with an adrenergic-dependent clinical and cellular phenotype with rectification abnormality enhanced by increased calcium. These findings are a significant advancement of our knowledge and understanding of phenotype-genotype relationship of arrhythmia syndromes related to KCNJ2 mutations.
Kir2.1; KCNJ2; inherited arrhythmia; CPVT3; ventricular arrhythmia; potassium inward-rectifier channel; genetic arrhythmia
Modulation of the autonomic nervous system has been used to treat refractory ventricular tachycardia (VT). Renal artery denervation (RDN) is under investigation for the treatment of sympathetic-driven cardiovascular diseases.
The purpose of this study was to report the largest case series to date using RDN as adjunctive therapy for refractory VT in patients with underlying cardiomyopathy.
Four patients with cardiomyopathy (2 nonischemic, 2 ischemic) with recurrent VT despite maximized antiarrhythmic therapy and prior endocardial (n = 2) or endocardial/epicardial (n = 2) ablation underwent RDN ± repeat VT ablation. RDN was performed spirally along each main renal artery with either a nonirrigated (6 W at 501C for 60 seconds) or an open irrigated ablation catheter (10–12 W for 30–60 seconds). Renal arteriography was performed before and after RDN.
RDN was well tolerated acutely and demonstrated no clinically significant complications during follow-up of 8.8 ± 2.6 months (range 5.0–11.0 months). No hemodynamic deterioration or worsening of renal function was observed. The number of VT episodes was decreased from 11.0 ± 4.2 (5.0–14.0) during the month before ablation to 0.3 ± 0.1 (0.2–0.4) per month after ablation. All VT episodes occurred in the first 4 months after ablation (2.6 ± 1.5 months). The responses to RDN were similar for ischemic and nonischemic patients.
This case series provides promising preliminary data on the safety and effectiveness of RDN as an adjunctive therapy in the treatment of patients with cardiomyopathy and VT resistant to standard interventions.
Renal denervation; Ventricular tachycardia; Cardiomyopathy; Ventricular tachycardia storm