Electronic Cardiac Pacemaker after Open-Heart Operations

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SINCE the advent of open-heart operations, surgical damage to the conduction system during operation has become prevalent. Complete atrioventricular (AV) block cannot always be avoided and has been a factor contributing to mortality, either immediately after the operation or later. Now, complete AV block has become reversible by means of cardiac pacemakers. A cardiac pacemaker provides a rhythmic electric stimulus to the ventricles to increase the ventricular rate. If the stimulus is adequate, the ventricles accept the rhythm imposed by the pacemaker, provided that it is faster than the intrinsic ventricular rhythm. Experimentally, in a dog with a sinus rhythm of 85 beats per minute, a heart rate of 90 can be imposed by the pacemaker, but not a rate lower than 85 (Fig. 1). In a dog with heart block and a ventricular rate of 40, any rate in excess of 40 can be imposed.

Zoll1 has designed a pacemaker for use with external electrodes. He advocates this mainly for treatment of diseases such as heart block with Stokes-Adams syndrome. Burchell2 uses a pacemaker with external electrodes to maintain the ventricular rate in patients who have AV block after open-heart operations.

Allen and Lillehei3 use a pacemaker that is connected to one electrode on the myocardium and to one under the skin. They have lost only one patient from AV block, of 40 consecutive patients who underwent open-heart operations. That patient, a child, died after he himself tore out the myocardial electrode. Allen and Lillehei3 have noted that in. . .



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