Effect of pacing current strength on indexes of myocardial activation in humans: influence of chronic infarction and polarity of pacing.

The effects of current strength (threshold to 20 mA) and pacing polarity (bipolar versus unipolar) on indexes of ventricular activation during endocardial pacing (cycle length 400 to 500 ms) from 10 normal and 17 abnormal left ventricular sites were assessed in 19 patients. Abnormal sites were infarcted and demonstrated an electrogram duration greater than 70 ms and amplitude less than 3 mV during sinus rhythm. Bipolar pacing was performed from poles 1 (cathode) and 3 (1 cm interelectrode distance) of a quadripolar catheter. Unipolar cathodal pacing was performed from the tip electrode (pole 1). Local activation was indexed by the interval from the pacing stimulus to 1) the onset of the QRS complex, 2) the largest rapid deflection of the local electrogram, and 3) the end (total duration) of the local electrogram recorded from poles 2 and 4 of the quadripolar catheter used for left ventricular pacing. Distant activation was indexed by the interval from pacing stimulus to electrograms recorded at the right ventricular apex and outflow tract. Bipolar and unipolar pacing of normal sites produced a modest homogeneous reduction of all activation times by 3 to 11 ms (median) with increments in current strength from threshold (0.8 mA) to 20 mA. Bipolar pacing of abnormal sites showed marked (up to 110 ms) and heterogeneous changes in local (median 22 to 30 ms) as well as distant (median 14 to 23 ms) activation times with increases in current strength from threshold (2.7 mA) to 20 mA.(ABSTRACT TRUNCATED AT 250 WORDS)