This study determines the direct effects of sympathetic denervation on excitability threshold and bipolar electrograms in acutely ischemic myocardium. Regional denervation was performed by application of phenol to the epicardium surrounding the ischemic zone in order to eliminate the possible hemodynamic effects that global cardiac denervation may exert on the ischemic zone. Data were obtained during serial occlusions (≤6 minutes in duration) of left anterior coronary artery in open-chest dogs with sympathetic denervation performed before the last occlusion. Late diastolic threshold was measured every 5 seconds by a constant voltage pacemaker which automatically registered threshold in stimulus duration. During ischemia, regional denervation (n = 9) increased peak excitability threshold from 240 ± 51 (standard error of the mean) to 552 ± 182 μs (p < 0.05) and prolonged electrographic duration in epicardium from 19 ± 3 to 25 ± 4 ms (p < 0.025) and in endocardium from 20 ± 3 to 25 ± 4 ms (p < 0.01). Phenol application did not alter aortic pressure, ischemic wall motion (sonomicrometer technique), or ischemic zone blood flow (microsphere technique). Thus, acute sympathetic denervation when limited to ischemic myocardium increases the peak excitability threshold and concomitantly prolongs duration of bipolar electrograms.
ASJC Scopus subject areas
- Cardiology and Cardiovascular Medicine