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Objectives . This study was conducted to assess the effectiveness of antitachycardia pacing modes and detection algorithms in patients with a new third-generation implantable cardioverter-defibrillator. Methods . Twenty-three of 42 consecutive patients had coronary artery disease, 14 had dilated cardiomyopathy, 2 had prior valve replacement and 3 had arrhythmogenic right ventricular dysplasia. The mean ejection fraction was 41 ± 14%; there were 31 men (74%) and 11 women, with a mean age of 53 years. On the basis of preoperative and postoperative electrophysiologic studies, in 28 patients antitachycardia pacing was postoperatively programmed randomly as “burst” (66%) or autodecremental “ramp” (34%) stimulation with a first coupling interval of 81% of tachycardia cycle length and up to 8 sequences with 3 to 10 stimuli. Results . During a follow-up interval of 6.3 ± 2.2 months, 15 patients were treated by antitachycardia pacing for a median of 6 (range 1 to 59) hemodynamically stable ventricular tachycardias (175 ± 12 beats/min). In 5 patients, 22 ventricular tachycardias (9%) were not terminated by antitachycardia pacing but by cardioversion. Seven (3%) of these episodes accelerated (>50 ms) during antitachycardia pacing. Syncope did not occur during these episodes. In seven patients initial antitachycardia pacing in cases of supraventricular tachycardias delayed charging and redetection prevented inappropriate discharges. Additional detection algorithms were programmed only after inappropriate therapy. The sudden “onset” and “sustained rate duration” criteria were programmed in three patients and the cycle length “stability” criteria in six patients, respectively. After activation of these detection algorithms only two of the seven patients had further inappropriate device discharges. Conclusions . Thus, antitachycardia pacing by this implantable cardioverter-defibrillator effectively and appropriately terminated 91% of hemodynamically stable ventricular tachycardias. Inappropriate device discharges were prevented in some patients by antitachycardia pacing and additional detection algorithms.

Objectives. The purpose of this study was to analyze and compare the local electrograms recorded at successful and unsuccessful sites of ablation to identify the criteria that may predict successful sites and minimize unnecessary radiofrequency delivery.Background. Transcatheter ablation of accessory pathways using radiofrequency energy requires extremely precise localization of an accessory pathway.Methods. Local electrograms from 50 consecutive patients with left-sided accessory pathways who underwent transcatheter radiofrequency ablation were analyzed. During catheter ablation, localization of accessory pathways was performed in 39 pathways during pre-excited sinus rhythm and in 14 pathways during orthodromic tachycardia. A total of 429 local electrograms at target sites obtained before delivery of radiofrequency current was analyzed. A prospective study was performed in another 20 patients using the criteria derived from the retrospective study.Results. Accessory pathway conduction block was achieved in 36 (92%) of 39 pathways in which mapping was performed during pre-excited sinus rhythm and in 9 (64%) of 14 pathways in which mapping was performed during orthodromic tachycardia (p < 0.05). When mapping was performed during pre-excited sinus rhythm, a combination of four variables (that is, an accessory pathway potential, stability of local electrograms, atrial activation > 1 mV and ventricular activation preceding the onset of the delta wave) showed a 62% probability of success. In contrast, excluding these variables resulted in a 95% probability of failure (noneffective or transiently effective). The prospective study shows that the use of these criteria can significantly reduce the number of current applications. When mapping was performed during orthodromic tachycardia, recording the earliest atrial activation was the most powerful predictor of success. A stable local electrogram with a small notch on the ventricular potential, presumed to be an accessory pathway potential, may add predictive value.Conclusions. Transcatheter radiofrequency ablation is highly effective in the treatment of patients with left-sided accessory pathways. Specific characteristics of local electrograms can be important predictors of success or failure. Mapping during preexcited rhythm renders ablation more effective than does mapping during orthodromic tachycardia.

The efficacy of propafenone in preventing induction of ventricular tachycardia was evaluated in 25 consecutive patients (mean age 62 ± 8 years) with remote myocardial infarction who underwent programmed electrical stimulation for ventricular arrhythmia using up to three extrastimuli after basic drive at the right ventricular apex. In nine patients (Group A), propafenone prevented induction of sustained ventricular tachycardia (noninducible in four, nonsustained [40 ms had a 94% positive predictive value for drug failure to prevent induction of ventricular tachycardia. Drug-induced percent prolongation of ventricular tachycardia cycle length in Group B did not correlate well with percent QRS prolongation. Rather, the best correlation was with percent prolongation of right ventricular effective (r = 0.72, p < 0.02) and functional (r = 0.73, p < 0.02) refractory periods at a basic drive of 400 ms.These observations suggest that excessive prolongation of conduction time in presumably normal tissue reduces the ability of propafenone to prevent ventricular tachycardia induction. It is speculated that effects of a drug on conduction time in partially refractory abnormal tissue forming the reentrant circuit may play a role in determining the tachycardia cycle length in the presence of that drug.