Determination of the sensitivity reserve of implantable electrostimulator to theR wave during cardiomyoplasty

Abstract

Measurement of the R wave amplitude and evaluation of the sensitivity reserve of implantable apparatus during cardiomyoplasty make it possible to prevent postoperation desynchronization of the electrostimulator. The sensitivity reserve for an ECS-445 electrostimulator is established. Measurements of acute R waves in 15 patients are presented. Key Words: cardiomyoplasty; acute electrocardiogram; R wave; electrostimulatorDesynchronization of implanted electrostimulator of the muscular blood pump (ESMBP) is a postoperation complication of cardiomyoplasty surgery. This complication very seldom arises from technical causes such as failure of myocardial electrode, pin jack, or ESMBP circuit. Desynchronization usually occurs when the amplitude of chronic R wave signal delivered by the myocardial electrode decreases below the sensitivity threshold of the implanted apparatus, This switches the cardiac channel of ESMBP to a regime of constant heart stimulation with a frequency below the proper heart rate. The interference of these rhythms may lead to grave ventricular arrhythmias up to ventricular fibrillation and, besides, it is usually accompanied by interference of muscular and cardiac contractions. When heart rhythm is out of control, some muscular contractions inevitably coincide with diastole.The loss of ESMBP sensitivity can be prevented by measuring the amplitude of acute R wave in order to determine its reserve with respect to the sensitivity threshold of the implanted apparatus [2]. Here we describe the technique and results of such measurements.The magnitude of this reserve should be specially discussed, since ESMBP produced by various manuMoscow Engineering and Physical Institute; I. P. Pavlov Medical University, St. Petersburg; Institute of Cardiology, Tomsk Research Center, Siberian Division of the Russian Academy ol Medical Sciences facturers have different minimum, settled, and maximum sensitivity threshold of the myocardial channel to the R wave. For instance, the minimum threshold in an ECS-445 electrostimulator (Elestim, Russia) is 1.5 mV, manufacturer's setting is 2.5 mV, and the maximum threshold is 8 mV, while the respective values for an SP1005 apparatus (Medtronic) are 0.6, 1.25, and 2.5 mV, respectively. Similar to implantable cardioverters, a 2-fold reserve of acute R wave with respect to minimum sensitivity threshold of the implanted ESMBP has been previously proposed [2]. Since the method for controlling the synchronization reliability was developed during clinical approbation of a STIMINAK-805 apparatus (Moscow Engineering and Physical Institute) with the only value of sensitivity threshold 3 mV [1], it was proposed that the amplitude of acute R wave (UR) during ftxation of the myocardial electrode should be no less than 6 mV (UR>6 mV) to ensure reliable functioning of the stimulator during the postoperation period.It should be noted that U~=6 mV assures and even surpasses the 2-fold reserve of the sensitivity threshold with respect to manufacturer's setting (2.5 mV). The use of manufacturer's ...