Faculty Bibliography

BACKGROUND: Strategies for prevention of sudden cardiac death focus on severe left ventricular (LV) dysfunction, although most sudden cardiac death postmyocardial infarction occurs in patients with mild/moderate LV dysfunction. We tested the hypothesis that infarct heterogeneity by cardiac magnetic resonance is associated with mortality beyond LV ejection fraction (LVEF) in patients with coronary artery disease and LV dysfunction. In addition, we examined the association between infarct heterogeneity and mortality in those with LVEF >35%. METHODS AND RESULTS: We studied 301 patients with coronary artery disease and LV dysfunction referred for cardiac magnetic resonance. We quantified total infarct mass, infarct core mass, and peri-infarct zone (PIZ) normalized for total infarct mass (%PIZ) using signal-intensity criteria of >2 SDs, >3 SDs, and 2- to -3 SDs above remote myocardium, respectively. Mean LVEF was 41 +/- 14%. After 3.9 years median follow-up, 66 (22%) patients died (13 sudden cardiac death; 33 with LVEF >35%). In patients with LVEF >35%, below-median %PIZ carried an annual death rate of 2.8% versus 12% in patients with above-median %PIZ (P<0.001). In a multivariable model, %PIZ maintained strong association with mortality adjusted to patient age, LVEF, right ventricular ejection fraction, prolonged QT interval, and total infarct size and resulted in improve risk reclassification 0.492 (95% confidence interval, 0.183-0.817). CONCLUSIONS: Cardiac magnetic resonance infarct heterogeneity has a strong association with mortality independent of LVEF in patients with coronary artery disease and LV dysfunction, particularly in patients with mild or moderate LV dysfunction. Further studies incorporating cardiac magnetic resonance in clinical decision making for defibrillator therapy are warranted.

BACKGROUND: Catheter ablation for ventricular tachycardia (VT) from structural heart disease has a significant risk of recurrence, but the optimal duration for in-hospital monitoring is not defined. This study assesses the timing, correlates, and prognostic significance of early VT recurrence after ablation. METHODS AND RESULTS: Of 370 patients (313 men; aged 63.0+/-13.2 years) who underwent a first radiofrequency ablation for sustained monomorphic VT associated with structural heart disease from 2008 to 2012, sustained VT recurred in 81 patients (22%) within 7 days. In multivariable analysis, early recurrence was associated with New York Heart Association classification >/=III (odds ratio [OR] 1.90, 95% confidence interval [CI] 1.03-3.48; P=0.04), dilated cardiomyopathy (OR 1.93, 95% CI 1.03-3.57; P=0.04), prevalence of VT storm before the procedure (OR 2.62, 95% CI 1.48-4.65; P=0.001), a greater number of induced VTs (OR 1.24, 95% CI 1.07-1.45; P=0.006), and acute failure or no final induction test (OR 1.88, 95% CI 1.03-3.40; P=0.04). During a median of 2.5 (1.2, 4.0) years of follow-up, early VT recurrence was an independent correlates of mortality (hazard ratio 2.59, 95% CI 1.52-4.34; P=0.0005). CONCLUSIONS: Patients who have early recurrences of VT after ablation are a high risk group who may be identifiable from their clinical profile. Further study is warranted to define the optimal treatment strategies for this patient group.

The assessment of risk in the asymptomatic patient with long QT syndrome can often be a challenging task, particularly when the available evidence is limited to relatively small retrospective registries, not to mention the need to consider the effect of individual patient factors which are often difficult to quantitate. We describe the relatively uncommon case of a man with a long-standing diagnosis of Long QT 2 syndrome who suffered his first cardiac event in his late 60's, likely precipitated by the development of paroxysmal atrial tachycardia. A brief review of the available literature on risk assessment in adults with genetically confirmed long QT syndrome who have remained asymptomatic late into adulthood will follow the case.

BACKGROUND: Entrainment criteria for macroreentrant arrhythmias are based on detecting fusion between tachycardia and paced wavefronts, but this is often difficult for atrial tachycardias (AT) after ablation of atrial fibrillation. METHODS AND RESULTS: With the use of a multipolar catheter, pacing was performed from electrodes within the coronary sinus showing activation later than adjacent electrodes (downstream overdrive pacing) during 66 ATs in 62 patients: 20 cavotricuspid isthmus-dependent ATs, 20 perimitral ATs, 13 focal ATs with sequential coronary sinus activation, and 13 other macroreentrant left atrial ATs. The paced cycle length was 10 to 30 milliseconds below the tachycardia cycle length (TCL), and activation at the neighboring upstream electrodes was assessed. Downstream overdrive pacing at 48 sites close to a macroreentrant circuit (PPI-TCL <40 milliseconds, where PPI is postpacing interval) produced constant fusion demonstrated by a long stimulus to upstream atrial electrogram interval (S-Au) >75% TCL and was consistent with orthodromic activation of the upstream site despite its close proximity to the pacing site. In contrast, downstream overdrive pacing at 18 sites during focal AT or remote from the macroreentrant AT circuit (PPI-TCL >40 milliseconds) always demonstrated a comparatively short S-Au <25% of TCL (12+/-4% versus 89+/-4% of TCL; P<0.001), consistent with direct activation. CONCLUSIONS: Selection of a downstream activation site for overdrive pacing can facilitate rapid recognition of macroreentry and proximity to the reentry circuit using a single multielectrode catheter by recognizing a PPI-TCL <40 milliseconds and S-Au >75% of TCL. Recognition of intracardiac constant fusion with this method is a novel criterion for transient entrainment.

INTRODUCTION: The need to detect impending implantable cardiac defibrillator (ICD) lead failure has grown. Automated sensing diagnostics have been developed for this reason. The sensing integrity counter (SIC) is one such oversensing diagnostic, which forms an integral part of the Medtronic lead integrity alert (LIA) feature on implantable defibrillators. It records nonphysiologic short VV intervals (NPSVVIs). It is unclear whether SIC data derived from integrated bipolar (IBP) leads need to be interpreted differently when compared to true bipolar (TBP) leads. We hypothesized that IBP ICD leads by virtue of a larger "antennae" may generate more NPSVVIs on than TBP leads, leading to more false-positive SIC counts. METHODS: Equal durations of remote monitoring records of 44 patients (mean age of 65.9 +/- 2.2 years, 52 % female) with IBP ICD leads and Medtronic (MDT) generators (IBP group) were compared with those of 44 randomly selected patients (64.0 +/- 2.2 years, 24 % female) who had TBP ICD leads and MDT generators (TBP group). Mean surveillance time, defined as the time over which the cumulative SIC count was acquired, was 614 +/- 44 days (TBP group) vs. 620 +/- 49 days (IBP group, p = ns). The mean time of follow-up following the first documented short VV interval was 115.2 months in the integrated bipolar group and 66.9 months in the true bipolar group. Leads on advisory were excluded from the study. RESULTS: A total of 26/44 patients in the IBP group displayed NPSVVI compared to 11/44 patients in the TBP group (59 vs. 25 %; p = 0.002, Fisher exact test). When adjusted for gender and lead age, the difference was still significant (p = 0.008). When evaluating the clinical consequence of NPSVVI in this cohort, 3/11 TBP leads with NPSVVI of >0 were eventually extracted due to additional abnormalities vs. 0/26 IBP leads with NPSVVI (p = 0.02, Fisher exact test). None of the IBP group patients with NPSVVI have developed inappropriate therapy from lead noise or a need for abandonment or extraction. CONCLUSION: Integrated bipolar ICD leads are more likely to have elevated SIC counts than true bipolar leads despite revealing no other evidence of lead failure. There does not appear to be a need for heightened surveillance in IBP leads with observed elevated SIC counts that have no other findings to suggest lead malfunction.

BACKGROUND: In the absence of overt structural heart disease, most left ventricular outflow tract ventricular tachycardias (VTs) have a focal origin and are benign. We hypothesized that multiple morphologies (MMs) of inducible left ventricular outflow tract VT may indicate a scar-related VT that can mimic idiopathic VT. METHODS AND RESULTS: Of 54 consecutive patients referred for ablation of sustained outflow tract VT without overt structural heart disease, 24 had left ventricular outflow tract VT, 10 had MM VT, and 14 had a single VT (SM). The MM group were older (70.3+/-4.3 versus 53.9+/-15.9 years; P=0.004), had more hypertension (100% versus 29%; P=0.0006), and had longer PR intervals and QRS durations compared with the SM group. In contrast to the SM group, the MM group VTs had features consistent with reentry, including induction by programmed stimulation without isoproterenol, entrainment in some, and abnormal electrograms in the periaortic area. Periaortic region voltages suggested scar in the MM group, but not in the SM group. MRI in 2 MM patients was consistent with scar, but not in 10 SM patients. Longer radiofrequency applications were required in the MM group than in the SM group. At a median follow-up of 9.7 (3.0-32.0) months, recurrences tended to be more frequent in the MM group than in the SM group (70% versus 22%; P=0.07). CONCLUSIONS: VTs from small regions of periaortic scar can mimic idiopathic VT but are suggested by multiple VT morphologies and are more difficult to ablate. Whether these patients are at greater risk, as feared for other scar-related VTs, warrants further study.

BACKGROUND: Cardiac resynchronization therapy (CRT) increases transmural dispersion of repolarization (TDR) and can be pro-arrhythmic. However, overall arrhythmia risk was not increased in large-scale CRT clinical trials. Increased TDR as measured by T(peak ) -T(end) (TpTe) was associated with arrhythmia risk in CRT in a single-center study. This study investigates whether QT interval, TpTe, and TpTe/QT ratio are associated with ventricular arrhythmias in patients with CRT-defibrillator (CRT-D). METHODS: Post-CRT-D implant electrocardiograms of 128 patients (age 71.3 years +/- 10.3) with at least 2 months of follow-up at our institution's device clinic (mean follow-up of 28.5 months +/- 17) were analyzed for QT interval, TpTe, and TpTe/QT ratio. Incidence of ventricular arrhythmias was determined based on routine and directed device interrogations. RESULTS: Appropriate implantable cardioverter-defibrillator therapy for sustained ventricular tachycardia or ventricular fibrillation was delivered in 18 patients (14%), and nonsustained ventricular tachycardia (NSVT) was detected but did not require therapy in 58 patients (45%). Patients who received appropriate defibrillator therapy had increased TpTe/QT ratio (0.24 +/- 0.03 ms vs 0.20 +/- 0.04, P = 0.0002) and increased TpTe (105.56 +/- 20.36 vs 87.82 +/- 22.32 ms, P = 0.002), and patients with NSVT had increased TpTe/QT ratio (0.22 +/- 0.04 vs 0.20 +/- 0.04, P = 0.016). Increased QT interval was not associated with risk of ventricular arrhythmia. The relative risk for appropriate defibrillator therapy of T(p) T(e) /QT ratio >/= 0.25 was 3.24 (P = 0.016). CONCLUSION: Increased TpTe and increased TpTe/QT ratio are associated with increased incidence of ventricular arrhythmias in CRT-D. The utility of TpTe interval and TpTe/QT ratio as potentially modifiable risk factors for ventricular arrhythmias in CRT requires further study.