Effect of implantable cardioverter-defibrillator shocks on QT dispersion

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.

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.

QT dispersion significantly increases after implantable cardioverter-defibrillator shocks

OBJECTIVE

To determine whether QT dispersion (QTd), a noninvasive electrocardiographic parameter of ventricular tachyarrhythmia risk assessment, is changed by implantable cardioverter-defibrillator (ICD) shocks delivered during implantation process, to analyze the duration of these changes, and to further evaluate the effect of amiodarone on these parameters.

METHODS

Twenty-six consecutive patients who are scheduled to undergo ICD implantation for aborted sudden cardiac death or documented symptomatic sustained ventricular tachycardia were enrolled into the study. A simultaneous 12-lead electrocardiogram (ECG) was recorded after the ICD implantation just before starting the testing shock when the patients were under general anesthesia (baseline record) and at 1st, 5th, 10th, 15th, 20th, 25th, and 30th minutes after the successful shocks. RR interval, QT interval, corrected QT interval (QTc), QTd, and corrected QTd (QTcd) were all measured and calculated on ECG.

RESULTS

At 1st minute after the successful shock, an abrupt increase (from 67.0 +/- 13.8 ms to 94.8+/-21 ms, P < 0.0001) was observed in QTcd, which was followed by a gradual return to the preshock values at 20th minute. Analysis of patients with and without long-term oral amiodarone treatment showed that in amiodarone-pretreated patients QTcd returned to the baseline value earlier than in patients without amiodarone treatment (15 minutes vs 20 minutes, respectively).

CONCLUSIONS

ICD shocks cause an increase in QTcd lasting for up to 20th minute, which may predominate in some important clinical problems like electrical storm. Amiodarone, with the desirable effect on QTcd, may reduce the proarrhythmic effects of ICD shocks.

Increase in QT/QTc dispersion after low energy cardioversion of chronic persistent atrial fibrillation

BACKGROUND

The effects of atrial internal cardioversion on QT interval and QT dispersion (parameters associated with increased risk of ventricular tachyarrhythmias) are unknown. We investigated changes in QT interval, QTc and QT dispersion immediately after shock delivery for internal cardioversion in patients with chronic persistent atrial fibrillation.

METHOD

Twenty-two patients with chronic persistent atrial fibrillation (mean duration, 17+/-23 months) underwent transvenous low-energy internal atrial cardioversion with a step-up protocol of shocks delivered between catheters in the right atrium and coronary sinus. (successful shock, 7.2+/-4.2 J). RR interval, QT interval, QTc interval, QT dispersion, and QTc dispersion were all measured on three consecutive beats (at 75 mm/s on at least 9 of 12 leads) and then averaged both before and after (1) the last unsuccessful shock, and (2) sinus rhythm restoration.

RESULTS

All parameters remained similar in the minute before and after the last unsuccessful shock. At 1 min after the successful shock, abrupt increases in QT dispersion (+43.8% vs. pre-shock; P<0.001 at least significant difference analysis) and QTc dispersion (+30.0%; P<0.05) were observed, followed by a gradual return to pre-shock values at 15 min.

CONCLUSIONS

These findings strongly suggest the likely existence of a brief period of increased electrical vulnerability immediately after restoration of sinus rhythm by internal cardioversion. Particular caution should therefore be applied whenever class III antiarrhythmic drugs are administered immediately after successful internal atrial cardioversion.

Inappropriate ICD Therapy Due to Proarrhythmic ICD Shocks and Hyperpolarization

A 50-year-old man with an ischemic cardiomyopathy underwent ICD implantation for inducible ventricular fibrillation (VF). Sixteen months later he experienced inappropriate ICD therapy due to atrial fibrillation with a rapid ventricular response. The initial shock resulted in the initiation of VF (proarrhythmia) and the patient received an additional shock converting his rhythm to an idioventricular rhythm with a cycle length of 490 ms (122 beats/min). Due to lead hyperpolarization, the device oversensed ventricular events and the patient subsequently received additional shocks.