Charles G. Walance

Reproducibility of arrhythmia induction with intracardiac electrophysiologic testing: Patients with clinical sustained ventricular tachyarrhythmias

In order to characterize the day to day reproducibility of arrhythmias provoked during electrophysiologic stimulation, 114 patients with documented sustained clinical ventricular tachyarrhythmias were studied. Two baseline electrophysiologic tests were performed in the drug-free state and within 6 to 24 hours of one another. There was a significant increment (p less than or equal to 0.02) in the induction of sustained ventricular tachyarrhythmias as the number of programmed extrastimuli increased from one (10% induction) to four (64% induction). Provoked arrhythmias were observed to be more frequently nonreproducible (as reflected in a major change in rate or duration, or both, of an induced ventricular arrhythmia between baseline tests) as the number of extrastimuli increased from one (7%) to four (27%). Nonreproducibility with three and four extrastimuli was not significantly greater than when two extrastimuli were utilized. Electrophysiology-directed drug trials should be interpreted in light of this observed variability in induced arrhythmias.

Assessment and follow-up of pediatric survivors of sudden cardiac death.

In the young patient resuscitated from sudden cardiac arrest, the risks of recurrence are uncertain and so are the criteria defining therapeutic efficacy for the presumed cause of the initial event. In this study, we analyzed the outcome of 15 consecutive young patients, who were resuscitated from pulseless ventricular tachycardia or ventricular fibrillation and who were evaluated by comprehensive hemodynamic and electrophysiological testing. Patients were 11.2 +/- 2.7 (mean +/- SD) years old at the time of their event, and each was known to have some form of heart disease before sudden cardiac arrest. Ventricular tachycardia or fibrillation was inducible by programmed electrical stimulation in eight patients. Accessory atrioventricular connections, with antegrade effective refractory periods less than 220 msec, were identified in three patients. Sustained atrial flutter was the only arrhythmia inducible in two patients, and no arrhythmias were inducible in two other patients. Surgical or electrophysiological-guided medical therapy resulted in noninducibility of the ventricular arrhythmias in six patients. Surgical division of the accessory atrioventricular connections was performed in three patients, and arrhythmias were not inducible after operation. The four patients with atrial flutter or without defined arrhythmia were treated with an empiric therapy. During 37 +/- 14 months of follow-up, the nine patients with documented noninducibility of a defined cause of sudden cardiac arrest were free of recurrent events. In contrast, during 18 +/- 10 months of follow-up, two of the six patients with empiric therapy or persistent inducibility of ventricular tachycardia died suddenly, and three others had recurrence of ventricular tachycardia or fibrillation.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of Local Electrogram Characteristics Correlated with Successful Radiofrequency Catheter Ablation of Accessory Atrioventricular Pathways

Due to the limited myocardial lesions produced by radiofrequency current, the ablation of accessory pathways (AP) requires precise localization of such connections. The purpose of this study was to ascertain ivhich characteristicfs) of the local bipolar electrogram, recorded from the ablation and adjacent electrode immediately prior to the application of radio/requency current, correlated with precision in localization adequate to permit AP ablation. Signal analysis was performed for 326 sets of electrograms preceding the attempted ablation of 107 APs in 100 consecutive patients. For 80 antegrade APs, the following variables were evaluated: (1) the presence or absence of an AP potential; (2) the local atrial‐AP interval; (3) the local atrioventricular (AV) interval; and (4) the relationship between the onset of local ventricular depolarization and onset of delta wave of the surface electrocardiogram. For the 27 concealed APs, the following characteristics were evaluated; (1) the presence or absence of an AP potential; and (2) the local VA interval during reciprocating tachycardia or ventricular pacing. Results: Antegrade APs: By statistical analysis, the best correlate of successful ablation of an antegrade AP was a local AV interval < 40 msec (positive predictive value = 94%; 95% confidence intervals (CI) = 81%–100%), Local AV intervals ≤ 50 msec preceded 88% of successful AP ablations, compared to only 8% of failed radiofrequency current applications. The positive predictive value of the other variables were: presence of an AP potential: 35% (95% CI = 27%–40%); local atrial‐AP intervals < 40 msec: 54% (95% CI = 43%‐66%); and local ventricular depolarization preceding onset of the delta wave 43% (95% CI = 34%‐52%). For concealed APs, the positive predictive value of a VA interval < 60 msec was 71% (95% CI = 48%–88%); the positive predictive value for the presence of an AP potential was 58% (95% CI = 32%–81%). Conclusions: No single electrogram characteristic had a positive predictive value and a sensitivity > 90% for AP localization adequate for radiofrequency current ablation. For antegrade APs, the best correlate of adequate localization was a local AV interval < 40 msec; as a corollary, radiofrequency current applications at sites where the local AV was > 60 msec, were unlikely to be effective. Objective criteria for the localization of concealed APs were less certain. Electrogram analysis, as a guide to AP localization and ablation, requires careful analysis of multiple variables, with analysis of the local AV interval a salient objective factor.

Day-to-day reproducibility of antiarrhythmic drug trials using programmed extrastimulus techniques for ventricular tachyarrhythmias associated with coronary artery disease

Forty-nine patients with coronary artery disease and documented clinical sustained ventricular tachycardia (VT) or ventricular fibrillation (VF) were studied twice in the drug-free state and twice during treatment with an identical antiarrhythmic medication at therapeutic plasma concentrations using an identical programmed electrical stimulation protocol. Tested drugs included procainamide, quinidine, disopyramide and phenytoin. During their 2 paired tests, 11 patients had nearly identical therapeutic plasma concentrations of antiarrhythmic agents (group I) and 38 patients had therapeutic plasma concentrations, but with more variation in drug levels between otherwise identical paired drug tests (group II). Overall, 71% of patients had inducible sustained VT or VF during drug testing. Induced ventricular arrhythmias were not reproducible in 45% of group I patients, despite restudy at nearly identical therapeutic plasma concentrations of an identical antiarrhythmic agent. Induced arrhythmias were also not reproducible in 16% of group II patients. This variability could not be attributed to the electrophysiologic characteristics of the patients studied. Drug trials directed by programmed stimulation should be cautiously interpreted because time-associated changes can mimic a change attributed to a beneficial or deleterious drug effect.

Limited value of programmed electrical stimulation from multiple right ventricular pacing sites in clinically sustained ventricular fibrillation or ventricular tachycardia associated with coronary artery disease

One-hundred and fifty patients with coronary artery disease and a documented history of sustained ventricular tachyarrhythmias were studied to determine if programmed electrical stimulation (PES) from a second right ventricular (RV) pacing site optimizes the induction of such sustained arrhythmias. The first PES test was performed from 2 RV pacing sites (apex and outflow tract or septum) using the apex first in each patient. All patients underwent a second PES within 6 to 24 hours of the first; both studies used up to 4 ventricular extrastimuli, in the absence of antiarrhythmic treatment. The second PES was performed from a single RV apical site using a pacing catheter retained from the first study. During the first days study, 74 patients (49%) had sustained ventricular tachycardia induced from the RV apex. Only 11 of the remaining 76 patients (7% of the total group) were inducible exclusively from a second RV pacing location during the first days testing. Seven of these 11 patients, as well as 15 additional patients who did not have ventricular tachycardia induced from either site on the first days study, were inducible from the RV apex during the second drug-free study. Among patients with sustained ventricular tachyarrhythmias, limiting PES to a single RV site, with the option of performing a second study in those who are initially noninducible is more effective in inducing sustained ventricular tachyarrhythmias than is PES performed from 2 RV pacing sites.

Ventricular fibrillation survivors in whom tachyarrhythmia cannot be induced: outcome related to selected therapy

Eight‐five patients were studied to determine the prognosis of the ventricular tachyarrhythmias at the time of electrophysiologic study. Twenty‐five patients (29%) were not inducible when we used a stimulation protocol consisting of up to four extrastimuli delivered at two right ventricular sites. Patients with no inducible arrhythmias were younger (53 vs 59 yrs; p = .06) and had higher ejection fractions (.49 vs .34; p < .04) than the inducible ventricular fibrillation survivors. Sex, cardiac diagnosis, time from event to electrophysiologic study, and antiarrhythmic therapy at the time of event did not discriminate between those with and those without inducible ventricular tachyarrhythmias. Survival free of recurrent sudden death or ventricular tachycardia was .86 ± .05 and .95 ± .05 for patients with and without inducible tachyarrhythmias, respectively (p = .22). Nine of 25 (36%) patients with no inducible arrhythmias developed inducible ventricular tachyarrhythmias when testing was repeated with an antiarrhythmic drug. Ventricular fibrillation survivors not inducible at the time of programmed ventricular stimulation (using a stimulation protocol consisting of four extrastimuli delivered at two right ventricular sites) seem to have a good prognosis. Many “noninducible” patients develop inducible tachyarrhythmias when placed on antiarrhythmic therapy. Because it is possible that these drugs are proarrhythmic, empiric antiarrhythmic therapy should be avoided in these patients.

Design and clinical application of a low-pass input filter for the evaluation of intracardiac electrograms during radiofrequency catheter ablation.

Successful ablation of an accessory pathway using radiofrequency current may be defined by the elimination of ventricular preexcitation or the loss of eccentric retrograde atrial activation.1 Because of the low voltages of intracardiac electrograms (0.1 to 5.0 mV) compared with the high voltages applied during radiofrequency ablation (30 to 50 V), monitoring of local electrograms during ablation may not be feasible with conventional biopotential amplification and filtering systems2. However, given the fundamental differences in signal frequencies between intracardiac electrograms (10 to 230 Hz) and radiofrequency current (550 to 750 KHz), selective attenuation of high-frequency radiofrequency signals and amplification of the lower frequency intracardiac electrograms may allow continuous monitoring of intracardiac electrograms during ablation.3 The purpose of this study was to evaluate the feasibility and clinical use of an input bandpass filter, selective for frequencies < 1 KHz, which allowed continuous monitoring of intracardiac electrograms in patients undergoing radiofrequency catheter ablation of accessory pathways.