Rates of upgrade of ICD recipients to CRT in clinical practice and the potential impact of the more liberal use of CRT at initial implant.

BACKGROUND: Many implantable cardioverter defibrillator (ICD) recipients may develop indications for cardiac resynchronization therapy (CRT) during follow-up. However, the actual upgrade rate during follow-up in clinical practice is not known. METHODS: We performed a single center retrospective observational study of all new ICD implants over 5 years (2003-2007). The rate of CRT upgrade of patients initially implanted with a single-/dual-chamber ICD during follow-up was assessed. The impact of using alternative criteria on the need for CRT in ICD recipients at initial implant was also evaluated. RESULTS: During the study period, there were 549 new ICD implants. The initial implant was a single/dual-chamber ICD in 73% (n = 399) and a CRT-D in 27% (n = 150). During follow-up (48±20 months) of the 399 ICD recipients, 70 (17.5%) died and 15 (3.8%) were upgraded to CRT, including eight cases where left ventricular lead implant had been initially unsuccessful. Upgrade rates at 1, 3, and 5 years were 0.03%, 2.4%, and 5.1%, respectively. Using alternative CRT criteria (left ventricular ejection fraction [LVEF]≤30%, QRS ≥130 ms, New York Heart Association I-IV) 42.6% (n = 234) of ICD recipients met criteria for CRT at initial implant. CONCLUSION: In this retrospective single center study, rates of CRT upgrade in ICD recipients over the medium term were low, which may reflect underuse in otherwise appropriate candidates. The more liberal use of CRT at initial implant in patients with a reduced LVEF, a broad QRS, but only mild heart failure symptoms would require approximately 50% increase in CRT use in ICD recipients at initial implant, and may help address some of the suggested underutilization.

Transseptal left ventricular endocardial pacing reduces dispersion of ventricular repolarization.

BACKGROUND: Cardiac resynchronization therapy (CRT) may be proarrhythmic in some patients. This may be due to the effect of left ventricular (LV) epicardial pacing on ventricular repolarization. The purpose of this study was to evaluate the effect of endocardial versus epicardial LV biventricular pacing on surface electrocardiogram (ECG) parameters that are known markers of arrhythmogenic repolarization. METHODS: ECG markers of repolarization (QT dispersion, QTD; T peak to end, T(peak-end) ; T(peak-end) dispersion, T(peak-end) D; QTc) were retrospectively measured before and after CRT in seven patients with transseptal LV endocardial leads (TS group), 28 matched patients with coronary sinus (CS) LV leads (CS group), and eight patients with surgical LV epicardial leads (SUR group). All ECGs were scanned and analyzed using digital callipers. RESULTS: Compared to the CS group, the TS group CRT was associated with a significant postpacing reduction in QTD (-45.2 ± 35.6 vs -4.3 ± 43.6 ms, P = 0.03) and T(peak-end) (-24.2 ± 22.1 vs 3.4 ± 26.7 ms, P = 0.02). There was a nonsignificant post-CRT reduction in both T(peak-end) D (-11.3 ± 31.0 vs 2.4 ± 28.9 ms, P = 0.27) and QTc (-50.0 ± 46.4 vs 4.4 ± 70.2 ms, P = 0.06) in the TS versus the CS group. In contrast, there were no differences between the SUR and CS groups in terms of the effect of CRT on these repolarization parameters. CONCLUSIONS: CRT with (atrial transseptal) endocardial LV lead placement is associated with repolarization characteristics that are considered to be less arrhythmogenic than those generated by CS (epicardial) LV lead placement. Further work is needed to determine whether these changes translate to a reduction in proarrhythmia.