Abstract 2321: Implantable Cardioverter-Defibrillator Shocks Increase T-Wave Alternans
Background: Re-initiation of ventricular tachyarrhythmias after shock-termination is a common phenomenon which carries a poor prognosis, but its mechanisms are poorly understood. We evaluated the impact of implantable cardioverter-defibrillator (ICD) shock on T-wave alternans (TWA), an index which may reflect heterogeneity of repolarization, a factor associated with ventricular arrhythmogenesis.
Methods: Sixty-five patients with ICDs underwent ambulatory ECG monitoring during defibrillation testing 3 months post-implant. TWA was analyzed continuously in the time domain during the baseline, sedated, and post-shock states. RR, QRS, and QT intervals and catecholamines were also measured continuously. Pacing was programmed VVI at 40bpm which allowed sinus rhythm with native conduction in all patients. Adequate pre- and post-shock holters were recorded in 55 patients, 48 male, mean 64 ± 12 years, 50 with coronary artery disease, 48 with prior spontaneous or induced arrhythmia.
Results: As shown in the table⇓, TWA significantly increased with shock, as did QRS duration, and norepinephrine and epinephrine levels, compared with sedated and baseline states. QT decreased. RR decreased minimally. TWA changes with shock were not associated with RR or QRS duration changes, but were significantly associated with changes in epinephrine.
Conclusions: ICD shock, even in the sedated state, increases heterogeneity of repolarization as measured by TWA, an effect mediated in part by sympathetic stimulation. This may help to explain the mechanisms of post-shock arrhythmia reinitiation.