Haemodynamic and clinical effects of paired stimulation of the heart.

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Abstract
The technique of paired stimulation of the heart is described and the hemodynamic results demonstrated in acute experiments conducted on 14 dogs. Paired stimulation was undertaken in 4 seriously ill patients, in 3 of whom a dangerous tachyardia was present; heart failure resistant to conventional therapy was present inthe 4th. Paired stimulation of the heart can be usedsuccessfully to slow arrhythmias of sinus, supraventricular or ventricular origin, both in dogs and in man. Electroaugmentation was demonstrated by an increase inthe 1st derivative of the ventricular pressure pulse (dp/dt), an increase in left ventricular systolic pressure, and a decrease in the end-diastolic pressure of the left ventricle during paired stimulation at heart rates identical to the control values. Despite the evidence of potentiation a hemodynamic improvement could only be demonstrated when the cardiac output was considerably reduced during the control period. Paired stimulation is potentially dangerous as the 2nd stimulus has to be applied close to the vulnerable phase of the ventricle and serious ventricular arrhythmias may be precipitated. Although capable of producing a profound positive inotropic action, this is at the expense of a corresponding increase in the 02 consumption of the myocardium. The indications for the technique in the clinical management of resistant arrhythmias and intractable heart failure have not yet been determined.