The advantages of transthoracic placement of permanent cardiac pacemaker electrodes

To determine the effect of stimulation site on cardiac pacing thresholds, identical, small-surface area, cathodal, Elgiloy electrodes were placed intramyocardially on the left and right ventricular apices and transvenously into the right ventricular apex of 20 dogs in complete heart block. At seven stimulus durations, threshold voltage and current were measured directly with an oscilloscope and current probe. Left ventricular intramyocardial pacing required less threshold stimulus energy than right ventricular intramyocardial or right ventricular endocardial pacing. Previous studies that determined lower thresholds with transvenous right ventricular endocardial leads than with directly placed myocardial leads used stimulating electrodes of differing configuration, surface area, and materials at the different sites and/or used epicardial rather than intramyocardial electrodes. These factors biased the results in favor of the endocardial site. When all clinical and electrophysiological facotrs are considered, direct intramyocardial placement of electrodes deserves a much wider acceptance and application than it now enjoys.