Chemical Ablation Of Purkinje Fibers Diminishes Spontaneous Activity In A Rat Model Of Regional Ischemia And Reperfusion

Spontaneous activity and arrhythmias associated with acute local ischemia and reperfusion were studied in isolated Langendorff-perfused hearts from healthy Sprague-Dawley rats (n=16). Epicardial fluorescence imaging of transmembrane potential and NADH were used to relate sources of electrical activity to changes in mitochondrial redox state caused by local ischemia. The left anterior descending coronary artery was cannulated and the flow of perfusate to the cannula was controlled by a high-pressure/low-flow HPLC pump. Studies were conducted using a local ischemia/reperfusion protocol that consisted of 10 min of normal flow, 20 min of regional LV ischemia, followed by 20 minutes of reduced flow reperfusion, and then 20 min of normal flow reperfusion. Control hearts (n=9) were compared with hearts in which the endocardium (containing the Purkinje fibers) was chemically ablated by applying a Lugol's iodine solution to the ventricular cavities (n=7). The ablation significantly reduced spontaneous activity in each phase of the protocol. Specifically, during acute regional ischemia, spontaneous activity was reduced by 80% (p<0.005); by 70% during low-flow reperfusion (p<0.005); and by 85% during full-flow reperfusion (p<0.001). Omission of blebbistatin, an electro-mechanical uncoupling agent, did not change the diminishing effect of the ablation on spontaneous activity (n=3). Epicardial imaging showed that spontaneous ectopic beats were manifested as concentric epicardial breakthrough patterns, located near spatiotemporal gradients of NADH fluorescence. These data strongly suggest that in un-paced hearts from healthy rats that are perfused with Tyrode's solution, the main mechanism of spontaneous ectopic activity associated with either ischemia, low-flow or full-flow reperfusion is activation of local Purkinje fibers.