Strength duration curve for left ventricular epicardial stimulation in patients undergoing cardiac resynchronization therapy.
INTRODUCTION
The strength duration curve has been studied for right ventricular endocardial stimulation. There are differences between left ventricular epicardial and right ventricular endocardial stimulation due to different electrophysiologic properties and different electrode-tissue interface. The strength duration curve for epicardial left ventricular stimulation has not been studied so far.


METHODS
One hundred and three patients were studied. The strength duration curves were determined for left ventricular epicardial and right ventricular endocardial stimulation. The studied points were chronaxie, rheobase, and voltage threshold at 0.5 ms. Left ventricular leads Guidant 4512, 4513, 4537, 4538 (unipolar, area 3.5 mm(2); Guidant Corp., St. Paul, MN, USA), Medtronic 4193 (unipolar, area 5.8 mm(2); Medtronic Inc., Minneapolis, MN, USA), Guidant 4518, 4542, 4543 (bipolar, area 4 mm(2)), St. Jude Medical (bipolar, area 4.8 mm(2); St. Jude Medical, St. Paul, MN, USA), and Medtronic 4194 (bipolar, area 5.8 mm(2)) were studied.


RESULTS
The Guidant unipolar leads with a distal electrode area of 3.5 mm(2) had a lower chronaxie than the other studied leads. The left ventricular epicardial and right ventricular endocardial chronaxie for 15 patients with Medtronic left ventricular leads 4194 or 4193 (5.8 mm(2)) and right ventricular leads 6947 (5.7 mm(2)) were 0.52 +/- 0.36 ms and 0.62 +/- 0.46 ms (P > 0.05).


CONCLUSION
The left ventricular epicardial chronaxie depends on the lead. The left ventricular epicardial chronaxie is similar to the right ventricular endocardial chronaxie for leads with similar electrode stimulation area.