Kishor Avasarala

Efficacy of implantable cardioverter defibrillators in young patients with catecholaminergic polymorphic ventricular tachycardia: Success depends on substrate

Background—The effectiveness of implantable cardioverter-defibrillator (ICD) therapy for the management of catecholaminergic polymorphic ventricular tachycardia (VT) in young patients is not known. ICD discharges are not always effective and inappropriate discharges are common, both resulting in morbidity and mortality. Methods and Results—This is a multicenter, retrospective review of young patients with catecholaminergic polymorphic VT and ICDs from 5 centers. ICD discharges were evaluated to determine arrhythmia mechanism, appropriateness, efficacy of therapy, and complications. A total of 24 patients were included. Median (interquartile range) ages at onset of catecholaminergic polymorphic VT symptoms and ICD implant were 10.6 (5.0–13.8) years and 13.7 (10.7–16.3) years, respectively. Fourteen patients received 140 shocks. Ten patients (42%) experienced 75 appropriate shocks and 11 patients (46%) received 65 inappropriate shocks. On actuarial analysis, freedom from appropriate shock at 1 year after ICD implant was 75%. Of appropriate shocks, only 43 (57%) demonstrated successful primary termination. All successful appropriate ICD discharges were for ventricular fibrillation. No episodes of polymorphic VT or bidirectional VT demonstrated successful primary termination. The adjusted mean (95% confidence interval) cycle length of successful discharges was significantly shorter than unsuccessful discharges (168 [152–184] ms versus 245 [229–262] ms; adjusted P=0.002). Electrical storm occurred in 29% (4/14) and induction of more malignant ventricular arrhythmias in 36% (5/14). There were no deaths. Conclusions—ICD efficacy in catecholaminergic polymorphic VT depends on arrhythmia mechanism. Episodes of ventricular fibrillation were uniformly successfully treated, whereas polymorphic and bidirectional VT did not demonstrate successful primary termination. Inappropriate shocks, electrical storm, and ICD complications were common.

Utility of Holter electrocardiogram in iron-overloaded hemoglobinopathies

Abstract: Cardiac arrhythmias are among the leading causes of morbidity and mortality of transfusion‐dependent, iron‐overloaded β‐thalassemia patients. Routine screening with Holter electrocardiogram has been recommended; however, infrequent electrocardiographic changes limit its clinical usefulness. The purpose of this study was to determine the diagnostic yield of Holter electrocardiogram monitoring and its correlation with patient symptoms and disease status. A retrospective analysis was performed on 27 transfusion‐dependent thalassemia patients who underwent cardiac questionnaire and Holter screening yearly, in addition to echocardiogram and quantitative iron‐level determination. Four patients had clinically significant arrhythmias detected on Holter screening, while 2 patients developed severe cardiac complications secondary to arrhythmias within 1 year of follow‐up of normal Holter screening. Early detection of cardiac events among transfusion‐dependent thalassemia patients with Holter electrocardiography is not clinically effective. Other screening modalities, including the transtelephonic event recorder, should be evaluated in arrhythmia surveillance.

Differential antagonism of cardiac actions of adenosine by theophylline

OBJECTIVE To determine the relative sensitivity of cardiac A1- and A2-adenosine receptor-mediated effects to antagonism by theophylline in man. METHODS Baseline measurements of the A-H interval (A1-adenosine receptor-mediated effect) and coronary blood flow (A2-adenosine receptor-mediated effect) were made in 10 patients with angiographically normal coronary arteries. Adenosine was then administered as a continuous intravenous infusion followed by a rapid intravenous bolus, and measurements repeated. Theophylline (5 mg/kg i.v.) was then administered, and the adenosine infusion repeated. To corroborate the results found in man, the cardiac A1- and A2-adenosine receptor-mediated effects were measured in guinea pig isolated hearts exposed to increasing concentrations of adenosine, in the absence and presence of theophylline (60 microM). RESULTS Compared to baseline, adenosine infusion and bolus caused significant prolongation of the A-H interval (109 +/- 41 vs. 116 +/- 44 vs. 168 +/- 57 ms, respectively), and increase in coronary blood flow (46 +/- 37 vs. 86 +/- 71 vs. 172 +/- 98 ml/min, respectively). Theophylline abolished the prolongation of the A-H interval during adenosine infusion and bolus (99 +/- 36 and 107 +/- 44 ms, respectively), yet had minimal effect on the increase in coronary blood flow (63 +/- 51 and 136 +/- 121 ml/min, respectively). In guinea pig isolated hearts, theophylline was shown to significantly antagonize the A2-adenosine receptor-mediated effects only when the concentrations of adenosine were < or = 1.0 microM. CONCLUSIONS In man, theophylline completely antagonizes the A1-adenosine receptor-mediated prolongation of the A-H interval, but has minimal effect on the A2-receptor-mediated coronary vasodilation, particularly when adenosine concentrations exceed 1.0 microM.

Are wide complex tachycardia algorithms applicable in children and patients with congenital heart disease

INTRODUCTION Several algorithms have been developed to help determine the etiology of wide complex tachycardias (WCTs) in adults. Sensitivity and specificity for differentiating supraventricular tachycardia (SVT) with aberration from ventricular tachycardia (VT) in adults have been demonstrated to be as high as 98% and 97%. These algorithms have not been tested in the pediatric population. We hypothesize that these algorithms have lower diagnostic accuracy in children and patients with congenital heart disease. METHODS A retrospective review of the pediatric electrophysiology database at Stanford from 2001 to 2008 was performed. All children with WCT, a 12-lead electrocardiogram (ECG) available for review, and an electrophysiology study confirming the etiology of the rhythm were included. Patients with a paced rhythm were excluded. The ECGs were analyzed by 2 electrophysiologists blinded to the diagnosis according to the algorithms described in Brugada et al,(2) and Vereckei et al.(5) Additional ECG findings were recorded by each electrophysiologist. RESULTS A total of 65 WCT ECGs in 58 patients were identified. Supraventricular tachycardia was noted in 62% (40/65) and VT in 38% (25/65) of the ECGs. The mean age was 13.5 years (SD ± 5.1), the mean weight was 51.8 kg (SD ± 22.4), and 48% (31/65) were male. The mean tachycardia cycle length was 340 milliseconds (SD ± 95). Congenital heart disease (CHD) was present in 37% (24/65) of patients (7 tetralogy of Fallot, 6 Ebsteins, 4 double-outlet right ventricle, 3 complex CHD, 2 d-transposition of great arteries, 1 status-post orthotopic heart transplantation, 1 ventricular septal defect). The Brugada algorithm correctly predicted the diagnosis 69% (45/65) of the time, the Vereckei algorithm correctly predicted the diagnosis 66% (43/65) of the time, and the blinded reviewer correctly predicted the diagnosis 78% (51/65) of the time. There was no difference in the efficacy of the algorithms in patients with CHD vs those with structurally normal hearts. The findings of left superior axis deviation (P < .01) and a notch in the QRS downstroke of V(1) or V(2) (P < .01) were more common in VT than SVT, whereas a positive QRS deflection in V(1) (P = .03) was more commonly present in SVT than VT. CONCLUSION The Brugada and Vereckei algorithms have lower diagnostic accuracy in the pediatric population and in patients with congenital heart disease than in the adult population. Left superior axis deviation and a notch in the QRS downstroke were more commonly associated with VT, whereas a positive QRS deflection in V(1) was more commonly associated with SVT in this population.

Electrocardiographic repolarization abnormalities and increased risk of life-threatening arrhythmias in children with dilated cardiomyopathy

BACKGROUND Life-threatening arrhythmia events (LTEs) occur in ~5% of children with dilated cardiomyopathy (DCM). While prolonged QRS duration has been shown to be associated with LTEs, electrocardiographic (ECG) repolarization findings have not been examined. OBJECTIVE We sought to determine the associations between ECG repolarization abnormalities and LTEs in children with DCM. METHODS A single-center retrospective review of children with DCM was performed. LTEs were defined as documented ventricular tachycardia or fibrillation requiring medical intervention. Three pediatric cardiologists, blinded to clinical events, evaluated ECGs obtained at the time of initial referral. Kaplan-Meier survival and Cox proportional hazards analyses were used to evaluate time to LTEs. RESULTS A total of 137 patients (mean age 7.8 ± 6.7 years; 75(55%) male patients) with DCM (mean ejection fraction 35% ± 16%) were included; 67 patients (49%) had a corrected JT (JTc) interval of ≥340 ms, 72 (53%) had a corrected QT (QTc) interval of ≥450 ms, and 41 (30%) had abnormal T waves. LTEs occurred in 15 patients at a median of 12 months (interquartile range 3-36 months) after the initial ECG. Patients with LTEs had a longer JTc interval (371 ± 77 ms vs 342 ± 41 ms; P = .02) and a longer QTc interval (488 ± 96 ms vs 453 ± 44 ms; P = .01). In survival analysis, a JTc interval of ≥390 ms (hazard ratio [HR] 4.07; 95% confidence interval [CI] 1.12-14.83; P = .03), a QTc interval of ≥510 ms (HR 6.95; 95% CI 1.53-31.49; P = .01), abnormal T-wave inversion (HR 11.62; 95% CI 2.75-49.00; P = .001), and ST-segment depression (HR 6.91; 95% CI 1.25-38.27; P = .03) were associated with an increased risk of LTEs, even after adjusting for QRS duration and amiodarone use. CONCLUSION Repolarization abnormalities are common in children with DCM. Certain ECG repolarization abnormalities, such as significantly prolonged JTc and QTc intervals, may be useful in identifying patients at risk of LTEs.

Ventricular lead redundancy to prevent cardiovascular events and sudden death from lead fracture in pacemaker-dependent children

BACKGROUND Children requiring a permanent epicardial pacemaker (PM) traditionally have a single lead placed on the right ventricle. Lead failure in pacemaker-dependent (PMD) children, however, can result in cardiovascular events (CVEs) and death. OBJECTIVE The purpose of this study was to determine if redundant ventricular lead systems (RVLS) can safeguard against CVE and death in PMD children. METHODS This was a single-center study of PMD patients undergoing placement of RVLS from 2002-2013. Patients ≤21 years of age who were PMD were included. Patients with a biventricular (BiV) system placed for standard resynchronization indications were excluded. RVLS patients were compared to PMD patients with only a single pacing lead on the ventricle (SiV). RESULTS Seven hundred sixty-nine patients underwent PM/implantable cardioverter-defibrillator placement with 76 BiV implants; 49 patients (6%) were PMD. Thirteen patients underwent implantation of an RVLS. There was no difference between the RVLS group (n = 13) and SiV PMD control group (n = 24) with regard to age (RVLS 9.5 ± 5.8 years vs SiV 9.4 ± 6.7 years, P = .52), weight (RVLS 38.2 ± 32.6 kg vs SiV 35.2 ± 29.3 kg, P = .62), indication for pacing, procedural complications, or time to follow-up. There were 2 lead fractures (17%) in the RVLS group (mean follow-up 3.8 ± 2.9 years), with no deaths or presentations with CVE. The SiV control group had 3 lead fractures (13%) (mean follow-up 2.8 ± 2.9 years), with no deaths, but all 3 patients presented with CVE and required emergent PM placement. CONCLUSION RVLS systems should be considered in children who are PMD and require permanent epicardial pacing. BiV pacing and RVLS may decrease the risk of CVE in the event of lead failure in PMD patients.

Catecholaminergic polymorphic ventricular tachycardia found in an adolescent after a methylenedioxymethamphetamine and marijuana-induced cardiac arrest.

Objective:To illustrate the challenges of managing patients with acute, undiagnosed arrhythmias through a case that demonstrates a possible association between catecholaminergic polymorphic ventricular tachycardia, a genetically determined severe arrhythmia disorder that often presents as either syncope or sudden death, and 3,4-Methylenedioxymethamphetamine (“Ecstasy”) combined with marijuana, which are often considered safe drugs by users. Design:Case report. Setting:Pediatric intensive care unit. Patient:A 15-yr-old male collapsed suddenly after ingesting an unknown substance and smoking marijuana. He was successfully resuscitated by first-responder chest compressions and rescue breaths along with a single 100-J shock by paramedics. He was intubated and transferred to a pediatric intensive care unit. Initial cardiac workup was negative but severe instability on vasopressors and a family history of intermittent palpitations and syncope in his brother raised suspicion for catecholaminergic polymorphic ventricular tachycardia. Identification of the unknown substance required coordination with a toxicology laboratory. Interventions:The patient had extremely labile cardiovascular responses to vasopressors. On day 5, his blood pressure was stable and he was extubated. A full cardiac workup, including a catheterization (preadmission to pediatric intensive care unit), electrocardiogram, cardiac magnetic resonance imaging were done to screen out most structural arrythmogenic diseases. A specific genetic test for catecholaminergic polymorphic ventricular tachycardia was sent. Measurements and Main Results:The patient’s methylenedioxymethamphetamine blood level was 87 ng/mL approximately 12 hrs after ingestion. Given the 3–8 hr half-life of methylenedioxymethamphetamine, it is likely that levels were toxic at the time of ingestion (>110 ng/mL). Marijuana may have provided a synergistic critical catecholamine release to trigger an arrhythmia. Genetic testing showed a ryanodine receptor-2 mutation that was consistent with catecholaminergic polymorphic ventricular tachycardia. Conclusions:While an initial cardiac workup for an acute, undiagnosed arrhythmia may be negative, family history may be a simple, essential component of patient management and disease diagnosis. This case demonstrates a possible association between methylenedioxymethamphetamine, marijuana, and catecholaminergic polymorphic ventricular tachycardia. All genetic and structural arrythmogenic disorders should be considered when working up a patient with presumed toxin-induced arrhythmias.

Ventricular pacing in single ventricles—A bad combination

BACKGROUND Chronic ventricular pacing (VP) is associated with systolic dysfunction in a subset of pediatric patients with heart block and structurally normal hearts. The effect of chronic VP in congenital heart disease is less well understood, specifically in the single-ventricle (SV) population. OBJECTIVE To determine the longitudinal effect of VP in SV patients. METHODS SV patients with heart block and dual-chamber pacemakers requiring >50% VP were compared with nonpaced (controls) SV patients matched for age, sex, and SV morphology. Patients were excluded if a prepacing echocardiogram was not available. Echocardiogram and clinical parameters were compared at baseline (prepacing) and at last follow-up in the paced group, and in controls when they were at ages similar to those of their paced-group matches. RESULTS Twenty-two paced and 53 control patients from 2 institutions were followed for similar durations (6.6±5 years vs 7.6±7.6 years; P = .59). There was no difference between groups regarding baseline ventricular function or the presence of moderate-to-severe atrioventricular valvar regurgitation (AVVR). Paced patients were more likely to develop moderate-to-severe systolic dysfunction (68% vs 15%; P < .01) and AVVR (55% vs 8%; P < .001) and require heart failure medications (65% vs 21%; P < .001). Chronic VP was also associated with a higher risk of transplantation or death (odds ratio, 4.9; 95% confidence interval, 1.05-22.7; P = .04). CONCLUSIONS SV patients requiring chronic VP are at higher risk of developing moderate-to-severe ventricular dysfunction and AVVR with an increased risk of death or transplantation compared with controls. New strategies to either limit VP or improve synchronization in this vulnerable population is imperative.

Is There a Difference in Tachycardia Cycle Length during SVT in Children with AVRT and AVNRT

There are limited adult data suggesting the tachycardia cycle length (TCL) of atrioventricular reentry tachycardia (AVRT) is shorter than atrioventricular nodal reentry tachycardia (AVNRT), though little data exist in children. We sought to determine if there is a difference in TCL between AVRT and AVNRT in children.

50 is the new 70: Short ventriculoatrial times are common in children with atrioventricular reciprocating tachycardia

BACKGROUND One of the basic electrophysiological principles of atrioventricular reciprocating tachycardia (AVRT) is that ventriculoatrial (VA) times during tachycardia are >70 ms. We hypothesized, however, that children may commonly have VA times <70 ms in AVRT. OBJECTIVE This study sought to determine the incidence and characteristics associated with short-VA AVRT in children. METHODS A retrospective single-center review of children with AVRT from 2000 to 2014 was performed. All patients ≤18 years of age with AVRT at electrophysiology study were included. Patients with persistent junctional reciprocating tachycardia, atrioventricular nodal reentry tachycardia, and tachycardia not unequivocally proven to be AVRT were excluded. VA time was defined as the time between earliest ventricular activation and earliest atrial activation in any lead and was confirmed by 2 electrophysiologists. Patients with VA times <70 ms (SHORT-VA) and those with standard VA times ≥70 ms (STD-VA) were compared. Logistic regression analysis identified characteristics of SHORT-VA patients. RESULTS A total of 495 patients with AVRT were included (mean age 11.7 ± 4.1 years). There were 265 patients (54%) with concealed accessory pathways (APs) and 230 (46%) with Wolff-Parkinson-White syndrome. AP location was left-sided in 301 patients (61%) and right-sided in 194 (39%). The mean VA time in AVRT was 100 ± 33 ms. A total of 63 patients (13%) had VA times <70 ms (SHORT-VA). The shortest VA time during AVRT was 50 ms. There was no difference in age, AV nodal block cycle, or body surface area between SHORT-VA and STD-VA patients, but SHORT-VA patients had lower weight (43 ± 17 vs 51 ± 23 kg, P = .02), lower AV nodal effective refractory period (AVNERP; 269 ± 50 vs 245 ± 52 ms, P < .01), and more left-sided APs (50 [79%] vs 251 [58%]; P < .01]. On multivariate logistic regression, factors associated with SHORT-VA included left-sided AP (odds ratio [OR] 5.79, confidence interval [95% CI] 2.21-15.1, P < .01), shorter AVNERP (OR 0.99, CI 0.98-0.99, P < .01), and lower weight (OR 0.97, CI 0.95-0.99, P < .01). CONCLUSIONS Children with AVRT can frequently have VA times <70 ms, with 50 ms being the shortest VA time. This finding debunks the classic electrophysiology principle that VA times in AVRT must be >70 ms. SHORT-VA AVRT was more common in children with left-sided APs.