EFFECT OF VENTRICULAR SHOCK STRENGTH ON CARDIAC HEMODYNAMICS

Ventricular Defibrillation and Cardiac Function. Introduction: The eff ect of implantable defibrillator shocks on cardiac hemodynamics is poo rly understood. The purpose of this study was to test the hypothesis t hat ventricular defibrillator shocks adversely effect cardiac hemodyna mics. Methods and Results: The cardiac index was determined by calcula ting the mitral valve inflow with transesophogeal Doppler during nonth oracotomy defibrillator implantation in 17 patients. The cardiac index was determined before, and immediately, 1 minute, 2 minutes, and 4 mi nutes after shocks were delivered during defibrillation energy require ment testing with 27- to 34-, 15-, 10-, 5-, 3-, or 1-J shocks. The car diac index was also measured at the same time points after 27- to 34-, and 1-J shocks delivered during the baseline rhythm. The cardiac inde x decreased from 2.30 +/- 0.40 L/min per m(2) before a 27- to 34-J sho ck during defibrillation energy requirement testing to 2.14 +/- 0.45 L /min per m(2) immediately afterwards (P = 0.001). This effect persiste d for > 4 minutes. An adverse hemodynamic effect of similar magnitude occurred after 15 J (P = 0.003) and 10-J shocks (P = 0.01), but dissip ated after 4 minutes and within 2 minutes, respectively. There was a s ignificant correlation between shock strength and the percent change i n cardiac index (r = 0.3, P = 0.03). The cardiac index decreased 14% a fter a 27- to 34-J shock during the baseline rhythm (P < 0.0001). This effect persisted for < 4 minutes. A 1-J shock during the baseline rhy thm did not effect the cardiac index. Conclusion: Defibrillator shocks > 9 J delivered during the baseline rhythm or during defibrillation e nergy, requirement testing result in a 10% to 15% reduction in cardiac index, whereas smaller energy shocks do not affect cardiac hemodynami cs. The duration and extent of the adverse effect are proportional to the shock strength. Shock strength, and not ventricular fibrillation, appears to be most responsible for this effect. Therefore, the detrime ntal hemodynamic effects of high-energy shocks may be avoided when low -energy defibrillation is used.