QT dispersion significantly increases after implantable cardioverter-defibrillator shocks

Inappropriate ICD shocks do not induce pro-arrhythmic electrocardiographic changes in men

OBJECTIVES

Longer-term electrocardiographic effects of multiple inappropriate ICD shocks were investigated to study their hypothesized pro-arrhythmic potential.

DESIGN

Thirteen male patients with ischemic cardiomyopathy who received ≥2 inappropriate shocks within 24 h and for whom 12-lead ECGs were available both before and within 72h after the inappropriate shocks were analyzed. Exclusion criteria included continuous ventricular pacing, underlying AF, events within 6 weeks after lead implantation and concomitant acute medical problems.

RESULTS

A total of 149 inappropriate shocks (mean 11 ± 19) were received. There were no significant differences in any of the measured intervals or morphological indices, nor was there a correlation between the "before-after" differences and the number of shocks received. Non-significant changes showed Percentage of Loop Area increase and relative T-wave Residuum decrease while the opposite changes have previously been associated with arrhythmic risk.

CONCLUSIONS

No potentially pro-arrhythmic electrocardiographic changes were found 19 h after multiple inappropriate shocks.

Etiology and Programming Effects on Shock Efficacy in ICD Recipients

BACKGROUND

We sought to assess the efficacy of high-energy shocks to restore rhythm and predictors of success in patients with sustained ventricular arrhythmias and implantable cardioverter defibrillator (ICD).

METHODS AND RESULTS

Data from 162 patients included in the UMBRELLA study that experienced one or more episodes of ventricular tachycardia (VT) for which ICD shocks of at least 30 Joules were delivered (appropriate high-energy shocks) were analyzed. In total, 456 ventricular arrhythmia episodes were registered. Forty four episodes (9.6%) from 39 patients (24%) had at least one ineffective high-energy shock delivered. Hypertrophic cardiomyopathy was more frequent among patients with unsuccessful shocks (10.3% vs 2.4%). Patients with ineffective shocks had higher proportion of sustained monomorphic ventricular arrhythmias (86.4%; the other 13.6% were sustained polymorphic and ventricular fibrillation [VF]) compared with patients with all their shocks effective (62.9%, P = 0.02). No statistical differences were found between groups in time from detection to the high-energy shock delivery, in tachycardia cycle length, or in antitachycardia pacing, but patients with ineffective high-energy shocks had higher proportion of previously ineffective low-energy shock (9.1% vs 0.5%, P = 0.01).

CONCLUSION

We found a substantial rate of ineffective high-energy shocks for the treatment of VT or VF in patients with ICD. High-energy shock efficacy seems to be reduced by hypertrophic cardiomyopathy and by the administration of previous low-energy shocks.

Effect of intravenous amiodarone on QT and T peak-T end dispersions in patients with nonischemic heart failure treated with cardiac resynchronization-defibrillator therapy and electrical storm

BACKGROUND

The effect of intravenous amiodarone on spatial and transmural dispersion of ventricular repolarization in patients receiving cardiac resynchronization therapy (CRT) remains unclear.

METHODS

We studied 14 patients with nonischemic heart failure who received CRT with a defibrillator, experienced electrical storm and were treated with intravenous amiodarone. Each patient underwent 12-lead electrocardiography (ECG) and 187-channel repolarization interval-difference mapping electrocardiography (187-ch RIDM-ECG) before and during the intravenous administration of amiodarone infusion.

RESULTS

A recurrence of ventricular tachyarrhythmia was observed in 2 patients during the early period of intravenous amiodarone therapy. Intravenous amiodarone increased the corrected QT interval (from 470±52 ms to 508±55 ms, P=0.003), but it significantly decreased the QT dispersion (from 107±35 ms to 49±27 ms, P=0.001), T peak-T end (Tp-e) dispersion (from 86±17 ms to 28±28 ms, P=0.001), and maximum inter-lead difference between corrected Tp-e intervals as measured by using the 187-ch RIDM-ECG (from 83±13 ms to 50±19 ms, P=0.001).

CONCLUSIONS

Intravenous amiodarone suppressed the electrical storm and decreased the QT and Tp-e dispersions in patients treated by using CRT with a defibrillator.

High-energy defibrillation increases the dispersion of regional ventricular repolarization

PURPOSE

This study evaluated the effects of shock energy on the dispersion of regional ventricular repolarization (DRVR), post-shock rhythm and sinus recovery time (SRT), and the relationship between DRVR and post-shock ventricular arrhythmias.

MATERIALS AND METHODS

Ten open-chest dogs were anesthetized. Ventricular fibrillation (VF) was electrically induced and recorded from a 6 × 6 unipolar electrode plaque (4 mm spacing) sutured on the left ventricular epicardium. Defibrillation threshold (DFT) was determined after 20 s of VF. DRVR was measured before VF, during the earliest post-shock sinus rhythm, and during sinus rhythm 30 s following shocks. Post-shock rhythm and SRT were evaluated after energies of 100% DFT, 125% DFT, 175% DFT, and 250% DFT.

RESULTS

In the100% DFT group, the DRVR of the earliest sinus rhythm and 30 s after successful defibrillation was not significantly different than that before VF. But the DRVRs were significantly increased in 125% DFT, 175% DFT, and 250% DFT group. DRVR after defibrillation in the 250% DFT group was higher than those in the 100% DFT and 125% DFT groups. SRT in the 250% DFT group was significantly longer than that in the other groups .The incidence of post-shock ventricular tachycardia was increased when a high-shock energy was applied (P = 0.041).

CONCLUSION

DRVR was increased by application of high-energy defibrillation associated with SRT prolongation. The increased DRVR may play an important role in the onset of post-shock ventricular tachycardia.