UNDERDETECTION OF VENTRICULAR-TACHYCARDIA USING A 40 MS STABILITY-CRITERION - EFFECT OF ANTIARRHYTHMIC THERAPY

Inappropriate shocks can complicate cardioverter defibrillator therapy . Among solutions proposed to avoid oversensing are algorithms to redu ce inappropriate detection of atrial fibrillation (AF) or sin us tachy cardia. In patients not an antiarrythmic drugs, an interval stability criterion of 40 ms has been validated with the Medtronic PCD to discri minate ventricular tachycardia (VT) from AF. With this algorithm, VT i s considered stable if no interval varies from one of the three preced ing intervals by more than 40 ms. If an interval does not fulfill this criterion, the VT event counter is reset to zero. The aim of this stu dy was to investigate the incidence of underdetection when this criter ion is applied in patients treated with antiarrhythmic drugs. We studi ed 132 sustained monomorphic VTs induced in 42 patients during 101 ele ctrophysiological studies (EPS). EPS were performed without treatment (group I, 24 patients, 44 VTs); on Class la drug (group II, 17 patient s, 24 VTs); Class Ic drug (group III, 22 patients, 39 VTs); or sotalol (group IV, 17 patients, 25 VTs). The endocardial electrogram of all V T episodes was digitized and the stability algorithm was applied. The reset arrhythmias were distributed among no delay, small, moderate (<1 0 s) and important (>15 s) delay in VT detection. The relation between drug use and reset was analyzed. Reset was found in 86 (65%) of induc ed VTs. No difference in heart rate or induction mode was shown betwee n reset and nonreset VTs. There was a significance association between drug use and reset probability (Chi(2) significantly different, P < 0 .05). In patients treated with Class Ic drugs, the probability of find ing an important delay in VT detection was 12.5% versus 0% in nontreat ed patients or in patients treated with sotalol. We conclude that a st ability criterion of 40 ms is probably safe in nontreated patients but should be used with caution in patients treated with antiarrhythmics, especially in the presence of Class Ic drugs.