Effects of DC electric countershock on ventricular function, cation balance and endogenous norepinephrine in the dog heart

Effects of DC electric countershock on cardiac function in thoracotomized dogs were evaluated from recordings of ECG, aortic pressure, left ventricular pressure and its first derivative, and coronary sinus flow. Samples of arterial and coronary venous plasma and left ventricular myocardium obtained before and after countershock at times corresponding to postshock arrhythmias and recovery were analyzed for Mg⁺⁺, K⁺ and Ca⁺⁺, and norepinephrine. At 1 min after countershock, ECG changes included transient cardiac arrhythmias and ST segment alterations, accompanied by depressed ventricular function and decreased myocardial Ca⁺⁺ concentration. At 5 min postshock, coronary venous Mg⁺⁺ and K⁺ concentrations had risen and ventricular function was still depressed. Function recovered within 10-20 min. There was no evidence of consistent loss of endogenous myocardial norepinephrine.