Paradoxical increase of ventricular fibrillation threshold in response to coronary sinus obstruction

Abstract

We determined the ventricular fibrillation threshold (VFT) changes in response to graded coronary sinus (CS) obstruction in 13 chloralose-anesthetized dogs with fixed heart rate (150 min −1, mean systemic arterial pressure (80 mm Hg), and cardiac index (100 ml/min · kg −1 body weight). VFT in milliamperes (VFT mA) increased linearily with CS pressure (CSP) increases up to 41.2 ± 1.4 mm Hg (VFT mA = 6.5 + 0.14 CSP mm Hg, p < 0.01). Total coronary venous effluent (CBF) did not change significantly, suggesting compensatory coronary vasodilation. Myocardial O 2 consumption also remained unchanged. At higher CSP, both CBF and VFT declined precipitously (VFT mA = 20.9 − 0.27 CSP mm Hg, p < 0.02). With simultaneous increases of systemic arterial along with CSP, VFT increased again along with the CSP-induced reduction of gradient until it reached 42.8 ± 3.2 mm Hg. We conclude that with coronary venous obstruction, despite coronary perfusion gradient reduction to about 40 mm Hg, CBF remains constant. This constant flow vasodilation is associated with substantial (82%) VFT increase. The mechanism may involve enhanced homogeneity of CBF distribution and increased extracellular fluid.