Naoki Naitoh

Frequency of presumed reentry with an excitable gap in sustained ventricular tachycardia unassociated with coronary artery disease

In sustained ventricular tachycardia (VT) unrelated to coronary artery disease, the incidence of reentry with an excitable gap was examined, and rapid pacing was performed to entrain VT in 48 episodes in 42 consecutive patients. Coronary artery disease was excluded by coronary arteriography. The underlying heart diseases were postoperative congenital heart diseases (n = 5), dilated (n = 7) or hypertrophic (n = 4) cardiomyopathy, arrhythmogenic right ventricular dysplasia (n = 6) and miscellaneous heart diseases (n = 5), as well as no demonstrable heart disease (n = 15) in which 8 patients had verapamil-responsive VT. Except for 1 patient with hypertrophic cardiomyopathy, 48 morphologically distinct monomorphic sustained VTs were induced. Twenty-five VTs showed right bundle branch block morphology and 23 left bundle branch block morphology, and VT was entrained in 84 and 96%, respectively. The overall incidence of the entrainment was 89.6% (43 of 48 monomorphic VTs), and the frequency of the ability to entrain VT ranged between 33.3 and 100% in the subgroups. The lowest frequency was found in hypertrophic cardiomyopathy. In conclusion, most inducible monomorphic sustained VT unassociated with coronary artery disease was presumed to be reentry with an excitable gap.

Catheter ablation with radiofrequency current of ventricular tachycardia originating from the right ventricle

Catheter ablation of ventricular tachycardia (VT) with radiofrequency current would be safer than the conventional ablation with direct current shocks. Seven patients who had eight morphologically distinct symptomatic monomorphic VTs underwent catheter ablation with radiofrequency current. The mean age +/- SD was 52 +/- 16 years, and the mean cycle length of the clinical VT was 298 +/- 36 milliseconds. Sustained VT was induced by programmed stimulation with or without isoproterenol in four patients and developed during the infusion of isoproterenol alone in two patients. Of these, four VTs were entrained with rapid pacing. The ablation was attempted at the site of earliest activation through the distal electrode and the external patch electrode on the back during VT in seven episodes in six patients. In the other patient it was applied during sinus rhythm. Energy was 40 to 50 W in the first case and 30 to 40 W in the others, and was given for 30 seconds. All VTs were terminated within 6 seconds, 3.6 +/- 0.8 seconds after the application of the radiofrequency current. Additional current was given to one to four predetermined sites by mapping. The mean number of applications was 4.0 +/- 1.3 sites. Except in the first patient, VT was eliminated successfully and VT was not induced by programmed stimulation, by the administration of isoproterenol, or by treadmill exercise testing. VT did not recur during the follow-up period of 6.8 +/- 1.1 months.

Electrophysiological Findings in Idiopathic Recurrent Ventricular Fibrillation: Special Reference to Mode of Induction, Drug Testing, and Long‐Term Outcomes

Electrophysiological studies can be useful in the presence of idiopathic ventricular fibrillation (VF) and may be used when selecting antiarrhythmic drugs. However, the yield, the mode, and the long‐term reproducibility of the induction of VF have not yet been fully elucidated. Eight patients with idiopathic VF underwent electrophysiological study. The mean age (± SD) was 45 ± 17 years. Six were males and two were females. Diagnosis was done by exclusion. VF was induced in 6 (75%) of 8 patients using double extra stimuli at coupling intervals of 233 ± 39 and 191 ± 20 ms for the first and second extra stimuli, respectively. Of note, VF was induced by stimulation exclusively at the origin of the premature ventricular beat, which was the first complex of VF in two patients. In another patient, VF was initiated by two premature stimuli and also by a pause produced by rapid pacing. The inducibility of VF was reproduced 9–18 months after the first induction in all of the four patients studied. When the ability of antiarrhythmic drugs to suppress VF inducibility was confirmed, no recurrence was observed during the follow‐up period of 40–160 months, but a recurrence of VF was observed in one of two nonresponders. In one patient, amiodarone administration failed in preventing VF induction 9 months after initiation of therapy, and reassessment of long‐term drug‐efficacy might be indicated in some patients. In conclusion, idiopathic VF was highly inducible (75%) with double extra stimuli. In this study, it was induced from a specific site (2/8) or by a pause (1/8). Induction of VF seemed to be reproduced 9–18 months after the first study. The outcome was considered favorable when the inducibility of VF was suppressed by antiarrhythmic drugs.

Alternation of QRS Morphology and Effect of Radiofrequency Ablation in Idiopathic Ventricular Tachycardia

We performed electrophysiological studies in 13 patients with idiopathic VT and attempted radiofrequency (RF) catheter ablation in 4 of them.Results: VT was induced by programmed stimulation in all patients and the mean cycle length was 363 ± 58 msec. In 8 of 13 patients (62%), alternation of either the cycle length and/or morphology of VT was observed. Transient entrainment was achieved in all patients by rapid pacing from the right ventricular outflow tract so reentry was considered the underlying mechanism of VT. The site of earliest activation (EAS) during VT was located at the apicoposterior portion of the left ventricular septum and used as the target site for RF catheter ablation. Spikelike presystolic activity was detected 20–40 msec prior to the large deflection of the local electrogram in four patients. VT was terminated by a few seconds of RF current in all four patients, but subsequently new VTs with a slightly different morphology were induced in three of them and re‐mapping showed a shift of the EAS. After additional RF ablation at the new EAS, VT was no longer induced. No complication was noted and VT did not recur during a follow‐up period for a mean of 9.3 ± 5.2 months.Conclusion: RF catheter ablation seems useful and safe for idiopathic VT. The alternation of QRS morphology and the findings at the time of catheter ablation suggest that an alternative pathway or multiple exits may be present in some patients with idiopathic VT, because the change in VT morphology was associated with a shift of the EAS.

Entrainment of Ventricular Tachycardia in Arrhythmogenic Right Ventricular Tachycardia

In two patients with arrhythrnogenic right ventricular dysplasia (ARVDJ, sustained ventricular tachycardia (VT) was induced by programmed stimulations during serial drug testings. One patient had five and the other had two VT morphologies, and the sites of origin were determined by endocardial catheter mappings. When overdrive pacing was performed, constant fusion in the QflS complex was observed in the two patients. Constant fusion of a different degree was also observed at different paced cycle lengths. Both patients had dilated right ventricles and wall‐motion abnormality, and the diagnosis of ARVD was further confirmed by the specimen resected at the site of origin of VT. Therefore, VT in ARVD can be entrained and reentry is the most likely mechanism of such VT.

Catheter ablation of ventricular tachycardia with radiofrequency currents, with special reference to the termination and minor morphologic change of reinduced ventricular tachycardia

During catheter ablation with radiofrequency (RF) currents, the incidence of the termination of reentrant ventricular tachycardia (VT) during application of RF energy and the morphologic change of the reinduced VT were analyzed. Twenty-five patients (20 men and 5 women, aged 44 +/- 17 years) were studied. After induction of monomorphic sustained VT, the ablation site was determined by endocardial activation mapping, identification of isolated mid-diastolic potential, and pacing during tachycardia. Thirty-six monomorphic VTs were induced in 25 patients and terminated with programmed stimulation. The cycle length was 323 +/- 55 ms and all VTs were entrained with rapid ventricular pacing. The target site was the earliest site of activation of VT in 26 VTs in 16 patients, and the area of slow conduction in 10 VTs in 9 patients. VT was terminated soon after the application of RF currents in 33 VTs in 22 patients at 6.0 +/- 3.1 seconds, and VT was induced immediately after the cessation of RF currents in 11 patients. Of these, 4 patients with idiopathic left ventricular VT had an alternation in the QRS configuration before catheter ablation and required repeat ablation of the other VT morphology. In the other 7 patients, such morphology was not observed before ablation, but was observed in VT induced when the original VT was terminated. Repeated attempts of catheter ablation 2 to 9 times at the remapped site was, however, successful in 7 of 8 VTs.(ABSTRACT TRUNCATED AT 250 WORDS)

Two Cases of Ventricular Parasystole Associated with Ventricular Tachycardia

In two patients, ventricular pamsystole (VP) was associated with ventricular tachycardia (VT), and in one patient, catheter ablation was successful. In patient 1, with dilated cardiomyopathy, VP led to VT, which converted to ventricular fibrillation. In patient 2, VP led to symptomatic nonsustained polymorphic VT. The origin of parasystolic focus was determined byendocardial mapping, and a radiofrequency current was delivered to patient 2. Both VP and VT disappeared immediately, and no recurrence has been observed during a follow‐up of 8 months. Catheter ablation to the parasystolic focus was effective and a relationship between VP and VT was strongly suggested.