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1.  Variability of action potential duration in pharmacologically induced Long QT Syndrome Type 1 
Long QT Syndrome (LQTS) is a congenital disorder associated with life-threatening arrhythmias. LQT1, a type of LQTS affecting the slow delayed rectifier potassium current, shows a higher incidence of arrhythmia associated with sympathetic stimulation than other types of LQTS. LQT1 patients show increased variability of repolarization with epinephrine infusion, as measured from the 12-lead ECG. We investigate the variability of repolarization measured as action potential duration (APD) in the rabbit left ventricle: how APD variability is affected by pacing rate, transmural location, LQT1 induced by chromanol 293b, and epinephrine infusion. Chromanol preferentially changes APD variability in the midwall. Infusing epinephrine returns the variability to nearcontrol levels. These results differ substantially from clinical studies and show the need for further study.
doi:10.1109/IEMBS.2009.5334105
PMCID: PMC4288588  PMID: 19964641
2.  A Multi-Center Study Comparing Shunt Type in the Norwood Procedure for Single-Ventricle Lesions: 3-Dimensional Echocardiographic Analysis 
Background
The Pediatric Heart Network’s (PHN) Single Ventricle Reconstruction Trial (SVR) randomized infants with single right ventricles (RV) undergoing a Norwood procedure to a modified Blalock-Taussig or RV-to-pulmonary artery shunt. This report compares RV parameters in the two groups using 3-dimensional echocardiography (3DE).
Methods and Results
3DE studies were obtained at 10/15 SVR centers. Of the 549 subjects, 314 underwent 3DE studies at one to four time points (pre-Norwood, post-Norwood, pre-stage II, and 14 months) for a total of 757 3DEs. Of these, 565 (75%) were acceptable for analysis. RV volume, mass, mass:volume ratio, ejection fraction (EF), and severity of tricuspid regurgitation did not differ by shunt type. RV volumes and mass did not change after the Norwood, but increased from pre-Norwood to pre-stage II (end-diastolic volume [EDV, ml]/body surface area [BSA]1.3, end-systolic volume [ESV, ml]/BSA1.3 and mass[g]/BSA1.3 mean difference [95% confidence interval] = 25.0 [8.7, 41.3], 19.3 [8.3, 30.4], and 17.9 [7.3, 28.5], then decreased by 14 months (EDV/BSA1.3, ESV/BSA1.3 and mass/BSA1.3 mean difference [95% confidence interval] = −24.4 [−35.0, −13.7], −9.8 [−17.9, −1.7], and −15.3 [−22.0, −8.6]. EF decreased from pre-Norwood to pre-stage II (mean difference [95% confidence interval] = −3.7% [−6.9%, −0.5%]), but did not decrease further by 14 months.
Conclusions
We found no statistically significant differences between study groups in 3DE measures of RV size and function, or magnitude of tricuspid regurgitation. Volume unloading was seen after stage II, as expected, but EF did not improve. This study provides insights into the remodeling of the operated univentricular RV in infancy.
Clinical Trial Registration
URL: http://www.clinicaltrials.gov. Unique identifier: NCT00115934.
doi:10.1161/CIRCIMAGING.113.000304
PMCID: PMC3904745  PMID: 24097422
echocardiography; heart defect; congenital; pediatrics
3.  Comparison of Fontan Survivors with and without Pacemakers: A Report from the Pediatric Heart Network Fontan Cross Sectional Study 
Congenital heart disease  2012;8(1):32-39.
Objective
Although many Fontan patients undergo pacemaker placement, there are few studies characterizing this population. Our purpose was to compare clinical characteristics, functional status and measures of ventricular performance in Fontan patients with and without a pacemaker.
Patients and Design
The NHLBI funded Pediatric Heart Network (PHN) Fontan Cross Sectional Study characterized 546 Fontan survivors. Clinical characteristics, medical history and study outcomes (Child Health Questionnaire (CHQ), echocardiographic evaluation of ventricular function, and exercise testing) were compared between subjects with and without pacemakers.
Results
Of 71 subjects with pacemakers (13%), 43/71 (61%) were in a paced rhythm at the time of study enrollment (age 11.9±3.4 years). Pacemaker subjects were older at study enrollment, more likely to have single left ventricles, and taking more medications. There were no differences in age at Fontan or Fontan type between the pacemaker and no pacemaker groups. There were no differences in exercise performance between groups. CHQ physical summary scores were lower in the pacemaker subjects (39.7±14.3 vs. 46.1±11.2, p = 0.001). Ventricular ejection fraction z-score was also lower (−1.4±1.9 vs. −0.8±2.0, p = 0.05) in pacemaker subjects.
Conclusions
In our cohort of Fontan survivors, those with a pacemaker have poorer functional status and evidence of decreased ventricular systolic function compared to Fontan survivors without a pacemaker.
doi:10.1111/j.1747-0803.2012.00692.x
PMCID: PMC3465639  PMID: 22762157
Fontan procedure; pacemaker; functional status; ventricular function
4.  Arrhythmias in a Contemporary Fontan Cohort: Prevalence and Clinical Associations in a Multi-Center Cross-Sectional Study 
Objectives
Our aim was to examine the prevalence of arrhythmias and identify independent associations of time to arrhythmia development.
Background
Since introduction of the Fontan operation in 1971, long term results have steadily improved with newer modifications. However, atrial arrhythmias are frequent and contribute to ongoing morbidity and mortality. Data are lacking regarding the prevalence of arrhythmias and risk factors for their development in the current era.
Methods
The Pediatric Heart Network Fontan Cross-Sectional Study evaluated data from 7 centers, with 520 patients aged 6–18 years (mean 8.6±3.4 years after the Fontan operation), including echocardiograms, electrocardiograms, exercise testing, parent-reported Child Health Questionnaire (CHQ) results, and medical history.
Results
Supraventricular tachycardias were present in 9.4% of patients. Intra-atrial reentrant tachycardia (IART) was present in 7.3% (32/520). The hazard of IART decreased until 4–6 years post-Fontan, and then increased with age thereafter. Cardiac anatomy and resting heart rate (including marked bradycardia) were not associated with IART. We identified three independent associations of time to occurrence of IART: lower CHQ physical summary score (p<0.001); predominant rhythm (p=0.002; highest risk with paced rhythm), and type of Fontan operation (p=0.037; highest risk with atriopulmonary connection). Time to IART did not differ between patients with lateral tunnel and extracardiac conduit types of Fontan repair. Ventricular tachycardia was noted in 3.5% of patients.
Conclusions
Overall prevalence of IART was lower in this cohort (7.3%) than previously reported. Lower functional status, an atriopulmonary connection and paced rhythm were determined to be independently associated with development of IART after Fontan.
doi:10.1016/j.jacc.2010.03.079
PMCID: PMC3200364  PMID: 20813285
Fontan; Intraatrial Reentrant Tachycardia; Arrhythmia; Congenital Heart Disease; Prevalence
5.  Vibrating Interventional Device Detection Using Real-Time 3-D Color Doppler 
Ultrasound image guidance of interventional devices during minimally invasive surgery provides the clinician with improved soft tissue contrast while reducing ionizing radiation exposure. One problem with ultrasound image guidance is poor visualization of the device tip during the clinical procedure. We have described previously guidance of several interventional devices using a real-time 3-D (RT3-D) ultrasound system with 3-D color Doppler combined with the ColorMark technology. We then developed an analytical model for a vibrating needle to maximize the tip vibrations and improve the reliability and sensitivity of our technique. In this paper, we use the analytical model and improved radiofrequency (RF) and color Doppler filters to detect two different vibrating devices in water tank experiments as well as in an in vivo canine experiment. We performed water tank experiments with four different 3-D transducers: a 5 MHz transesophageal (TEE) probe, a 5 MHz transthoracic (TTE) probe, a 5 MHz intracardiac catheter (ICE) transducer, and a 2.5 MHz commercial TTE probe. Each transducer was used to scan an aortic graft suspended in the water tank. An atrial septal puncture needle and an endomyocardial biopsy forceps, each vibrating at 1.3 kHz, were inserted into the vascular graft and were tracked using 3-D color Doppler. Improved RF and wall filters increased the detected color Doppler sensitivity by 14 dB. In three simultaneous planes from the in vivo 3-D scan, we identified both the septal puncture needle and the biopsy forceps within the right atrium using the 2.5 MHz probe. A new display filter was used to suppress the unwanted flash artifact associated with physiological motion.
doi:10.1109/TUFFC.2008.798
PMCID: PMC2639786  PMID: 18599423
6.  Spatial Heterogeneity of the Restitution Portrait in Rabbit Epicardium 
Spatial heterogeneity of repolarization can provide a substrate for reentry to occur in myocardium. This heterogeneity may result from spatial differences in APD restitution. The restitution portrait (RP) measures many aspects of rate-dependent restitution: the dynamic restitution curve (RC), S1-S2 RC, and short-term memory response. We used the RP to characterize epicardial patterns of spatial heterogeneity of restitution that were repeatable across animals. NZW rabbit ventricles were paced from either the epicardial apex, mid-ventricle, or base, and optical action potentials were recorded from the same three regions. A perturbed downsweep pacing protocol was applied that measured the RP over a range of cycle lengths from 1000-140 ms. The time constant of short-term memory measured close to the stimulus was dependent on location. In the mid-ventricle the mean time constant was 19.1±1.1 sec, but it was 39% longer at the apex (p<0.01) and 23% longer at the base (p=0.03). The S1-S2 RC slope was dependent on pacing site (p=0.015), with steeper slope when pacing from the apex than from the base. There were no significant repeatable spatial patterns in steady-state APD at all cycle lengths or in dynamic RC slope. These results indicate that transient patterns of epicardial heterogeneity of APD may occur following a change in pacing rate. Thus, it may affect cardiac electrical stability at the onset of a tachycardia or during a series of ectopic beats. Differences in restitution with respect to pacing site suggest that vulnerability may be affected by the location of reentry or ectopic foci.
doi:10.1152/ajpheart.00619.2006
PMCID: PMC2003335  PMID: 17122194
rate dependence; short-term memory; dynamic restitution curve; S1-S2 restitution curve; action potential duration

Results 1-6 (6)