The AFFIRM Study enrolled 4060 predominantly elderly patients with atrial fibrillation to compare ventricular rate control with rhythm control. The patients in the AFFIRM Study were representative of patients at high risk for complications from atrial fibrillation, which indicates that the results of this large clinical trial will be relevant to patient care.
Endocardial recordings from a patient with both sustained ventricular tachycardia and AV nodal reentrant tachycardia are presented that demonstrate spontaneous transient entrainment of ventricular tachycardia by AV nodal reentrant tachycardia. During electrophysiological catheterization, there were repeated episodes of spontaneous conversion from a wide to a narrow QRS morphology following the induction of ventricular tachycardia. With conversion from the wide to the narrow QRS, the ventricular deflection in the coronary sinus electrograms demonstrated an abrupt change in morphology, indicating a change in activation sequence at this site from the wavefront of depolarization emerging from the ventricular tachycardia circuit to a wavefront conducting over the His‐Purkinje system. However, the right ventricular apex electrogram demonstrated a constant morphology with a decrease in cycle length equal to that of the other intracardiac electrograms, indicating a constant direction of activation from the ventricular tachycardia circuit, and that ventricular tachycardia had been transiently entrained by AV nodal reentrant tachycardia. In addition, rapid atrial pacing during ventricular tachycardia narrowed the QRS and demonstrated transient entrainment of the right ventricular apex electrogram. Although transient entrainment of a tachycardia is evidence supporting reentry with an excitable gap as the probable mechanism, its demonstration has required the use of rapid pacing techniques. This case is a spontaneously occurring example of transient entrainment of one tachycardia circuit by another, a phenomenon that has not been previously described.
Antiarrhythmic drugs have no consistent effects on the signal-averaged electrocardiogram (ECG) while successful surgical ablation of ventricular tachycardia is known to abolish late potentials. Ten patients with prior myocardial infarction had successful ablation of recurrent sustained ventricular tachycardia by selective ethanol infusion into a small coronary vessel supplying the tachycardia origin. Signal-averaged ECGs were performed before and after initially successful ablation in patients without pacemaker dependence or intraventricular conduction delay to assess the effects on late potentials and to determine if the signal-averaged ECG could predict ventricular tachycardia recurrence. Only four of ten patients were eligible for study and all four had late potentials prior to ethanol ablation. Late potentials were abolished in one patient who has not had an arrhythmia recurrence in 25 months. One patient with sudden death and another patient with ventricular tachycardia recurrence had persistent late potentials post procedure that were modified by a reduction in terminal voltage and lengthening of terminal low amplitude signal. The fourth patient who receives chronic amiodarone had no arrhythmia recurrence in spite of persistent but modified late potentials. Thus, the abolition of late potentials after ethanol ablation may predict freedom from arrhythmia recurrence.
Just as a stable defibrillation threshold is required for implantable defibrillators to maintain efficacy and a margin of safety for the conversion of life-threatening ventricular arrhythmias, a stable pacing threshold is also required to provide bradycardia support and pacing to terminate ventricular tachycardias. This article reports the temporal course of pacing thresholds in patients treated with a tripolar, tined endocardial defibrillator lead capable of bipolar sensing and pacing, and defibrillation. Seventeen patients who underwent implantation of an implantable defibrillator system using an integrated bipolar pacing/sensing system were prospectively studied over 18 months. There were 16 males and one female, with a mean age of 69 +/- 5 years (range 61-75 years). At implantation, predischarge, and every 2 months thereafter, the pacing pulse-width threshold was tested at both 2.5 and 5.0 V stimulus amplitudes. After a mean follow-up of 363 +/- 173 days (range 34-597 days), the pacing threshold increased from 0.08 +/- 0.08 ms to 0.5 +/- 0.3 ms at the 2.5 V amplitude (p < or = 0.01, CI-0.57 to -0.27) and from 0.04 +/- 0.02 ms to 0.25 +/- 0.14 ms at the 5.0 V amplitude (p < or = 0.01, CI -0.28 to -0.14). Eight of the 17 patients (47%) received spontaneous implantable defibrillator shocks for clinically detected arrhythmias, and the total number of joules delivered via the leads did not correlate with the pacing threshold changes. We conclude that the pacing threshold for the nonthoracotomy implantable defibrillator lead system studied is not stable and increases with time. This finding has implications for defibrillator battery life in patients who use implantable defibrillators for bradycardia pacing.
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