Effects of left ventricular lead positions and coronary venous microanatomy on cardiac pacing parameters

We describe effects of pacing lead position and cardiac microanatomy on electrical pacing parameters. Passive fixation transvenous pacing leads were implanted in anterior interventricular veins in isolated swine hearts (n = 6). Electrical pacing parameters were measured in 3 implant positions (5 implant sites each): touching myocardial side of venous wall, not touching venous wall, and touching epicardial side of venous wall. After perfusion fixing hearts, veins were sectioned perpendicular to vein's length from base to apex. Slides were prepared and analyzed for measurement of vein wall thickness/circumference, and distances between vein walls and myocardium. Average pacing thresholds were greater when pacing leads were free-floating (5.45 ± 3.29 V) or oriented in epicardial positions (6.81 ± 2.96 V) compared with myocardial positions (3.79 ± 3.46 V; P = not significant). Vein circumferences were significantly larger in basal regions (8.31 ± 2.28 mm) compared with mid (6.90 ± 1.46 mm) and apical (6.40 ± 1.92 mm) regions (P < .05). Variability in pacing thresholds and impedances indicates that pacing lead placement in left ventricular coronary veins significantly affects electrical pacing parameters.