COMBINING MONOPHASIC ACTION-POTENTIAL RECORDINGS WITH PACING TO DEMONSTRATE DELAYED AFTERDEPOLARIZATIONS AND TRIGGERED ARRHYTHMIAS IN THE INTACT HEART - VALUE OF DIASTOLIC SLOPE

Background In the intact heart, methodological difficulties hamper the direct visualization of delayed afterdepolarizations (DADs) responsib le for triggered arrhythmias. Therefore, we tested the hypothesis that a combination of pacing and the recording of a monophasic action pote ntial (MAP) could facilitate the recognition of ouabain-induced DADs a nd triggered arrhythmias by demonstrating an increase in the diastolic baseline slope (dV/dT) of the MAP recording at the end of a pacing tr ain. Methods and Results In anesthetized dogs with chronic atrioventri cular block, a right ventricular endocardial MAP was recorded during ( 1) control (n=11), (2) 15 to 45 minutes after administration of ouabai n (45 +/- 10 mu g/kg, n=11), (3) 10 minutes after administration of li docaine (3 mg/kg, n=5), and (4) during lidocaine washout (n=3). Pacing was performed with the MAP catheter. Also, the protocol was performed in 3 dogs with conducted sinus rhythm during control and ouabain circ umstances. During control, the slope Value was 2 +/- 2 m V/s (mean +/- SD), the incidence of DADs after the stimulation train was 6%, and no ventricular tachycardias (VTs) were induced in dogs with atrioventric ular block. During ouabain administration, the slope and DAD incidence s increased to, respectively, 26 +/- 14 m V/s and 74% (P<.05 for both) . VTs were induced frequently. Lidocaine prevented VT induction by dec reasing the slope and the incidence of DADs. This effect disappeared a fter lidocaine washout. During conducted sinus rhythm, similar results were found. Conclusions By combining pacing and MAP recordings, the d iastolic slope observed on MAP recordings in ouabain-intoxicated heart s can be used as a marker for DADs and triggered arrhythmias. This fin ding may be helpful in identifying triggered activity in the intact he art.