R-wave Sensing Problem and its Solution in A-V Sequential Demand Pacemaker

Abstract

Ventricular pacing has recently become widely popular along with notable improvements made in the engineering aspects, and its application has gradually widened.
In our experiments, permanent and temporary pacings have been used respectively on the patients suffering from complete A-V block and on those in postoperative state with satisfactory results.
However, in some patients, who had been in far advanced cardiac dysfunction, ventricular pacing itself has been found inadequate to improve deteriorated postoperative cardiac functions, although it has proved sufficient to control arrhythmias. The reason is based on the negation of atrial contraction which is known to boost cardiac function up to 20 to 30 per cent when it is synchronized with ventricular contraction.
Subsequently, we have developed a new A-V sequential demand pacemaker to apply temporarily to patients immediately after open heart surgery and confirmed its electrical safety and reliability along with satisfactory hemodynamic response.
In this paper, we report the results obtained from this device, putting special emphasis on its R-wave sensibility.
To make clinical application easier, unipolar stimulation was used on the atrium and the ventricle. However, the problem which related to unipolar stimulation was the interference against ventricular demand mechanism by the atrial stimulation, resulting in malfunction of the demand system.
After investigating the property of this interfering wave in detail, we found that the cause was in the indifferent electrode.
Two methods of sensing R-wave are introduced. One employs a simulator which cancels the interfering wave for the ventricular electric potential, the other employs the direct current feedback circuit and two indifferent electrodes for the atrial stimulation and R-wave sensing. These methods have been proved to work perfectly with the ECG.