Effects of DC Electric Countershock on Ventricular Function, Cation Balance and Endogenous Norepinephrine in the Dog Heart

Abstract

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 post-shock 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 post-shock, 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

The Defibrillation Conundrum: New Insights into the Mechanisms of Shock-Related Myocardial Injury Sustained from a Life-Saving Therapy

“…This direct and immediate effect could explain a transient decrease in myocardial contractility. In addition, cell death leads to the rapid release of large quantities of cations (Mg ++ , K + ) into the extracellular environment, with consequences for cardiac inotropism in addition to proarrhythmic effects [ 85 ].…”