DIFFERENTIAL-EFFECTS OF CHANGES IN LOCAL MYOCARDIAL REFRACTORINESS ONATRIAL AND VENTRICULAR LATENCY

Background Assessment of myocardial refractoriness and conduction prop erties. critical to development and propagation of reentrant arrhythmi as, is an integral part of the investigation of atrial and ventricular tachycardias through the use of programmed electrical stimulation. Lo cal conduction itself, however, may be affected by myocardial refracto riness. Methods and Results We studied the effects of changes in myoca rdial refractoriness on local conduction in right atrial and ventricul ar myocardium in 19 patients. Changes in effective, functional, and re lative refractoriness were accomplished with the use of four pacing pr otocols, including drive train pacing cycle lengths (PCLs) of 600 and 400 milliseconds (ms) and drive train durations (DTDs) of 8 and 50 sti muli. Unipolar cathodal stimulation was performed from the distal elec trode, and unipolar electrograms were recorded from the proximal three poles of quadripolar catheters with 5-mm interelectrode spaces. Atria l and ventricular effective and relative refractory periods (ERPs and RRPs) were significantly shortened by bulb the reduction in PCL and th e increase in DTD. The reduction in the PCL shortened atrial and ventr icular refractory periods significantly more than did the increase in the DTD. Changes in ventricular refractory periods were significantly greater compared with atrial refractory periods. The ratio or RRP to E RP was reduced in the atrium but significantly increased in the ventri cle with reduction in PCL and increase in DTD. For all premature inter vals, the conduction interval from stimulus to the first recording ele ctrode pole was significantly greater than conduction intervals measur ed between subsequent electrode poles. The greatest increase in conduc tion interval with closely coupled premature complexes occurred betwee n the stimulus artifact and the first recording electrode pole. Reduct ion in ventricular but not atrial ERP was associated with significantl y increased local conduction interval. Conclusions First, most of the conduction delay after the stimulus artifact occurs within 5 mm from t he pacing site. Second, closely coupled premature complexes delay cond uction primarily by prolonging latency in the first 5 mm from the paci ng site. Third, fundamental differences occur between the atrium and v entricle regarding changes in local conduction as a function of change s in ERP, suggesting that factors involved in sudden changes in refrac toriness (eg, heart rate acceleration) could produce divergent effects on atrial and ventricular arrhythmogenesis.