Desenvolvimento e teste de um dispositivo para estimulação torácica externa com função de marca-passo e avaliação da eficácia da estimulação cardíaca mecânica

Abstract

The transcutaneous pacemaker has been used as therapy in cases of bradycardia with hemodynamic impairment, but it has important limitations, due to the high energy required to promote myocardial activation, causing discomfort and muscle stimulation. Thus, alternative forms of artificial cardiac stimulation have been the object of studies. Mechanical stimulation is capable of causing cardiac activation and functioning as a pacemaker, similarly to activation by an electrical stimulus. A mechanical stimulus of a certain intensity can generate a mechanical deformation in the myocardium capable of initiating myocardial excitation, resulting in ventricular contraction. This work comprises two parts: the development and testing of a prototype electropneumatic device for transthoracic cardiac pacing in humans, and the performance of an experimental study aimed to assess the efficacy the of mechanical cardiac stimulation, comparing this form of stimulation with standard electrical stimulation, regarding cardiac activation, maintenance of ventricular command and induction of ventricular arrhythmia. Hearts from 10 adult toads (402 ± 101 g) of both sexes were partially exposed outside the body and randomly submitted to mechanical or electrical stimulation. Two pairs of copper electrodes were implanted to monitor and stimulate the heart. Mechanical stimulation was performed by means of a back-and-forth movement and impact of a 2 mm diameter metal rod on the external surface of the left ventricle (aiming at the lateral wall and apex). The electrical ventricular stimulation was provided by programmed temporary pacemaker generator in demand mode connected to two pacing wire leads. After performing the threshold measurements, each form of stimulation was maintained for five minutes, with an HR of 10 bpm above the baseline HR of each animal, maintaining the same energy and HR during each phase of the experiment. The electropneumatic device tested showed a linear correlation between the mechanical energy released and the pressure of the compressed air, providing increasing energy values within the predicted range for transthoracic cardiac pacing (considering a threshold of 0.04 to 1.5 J), reaching up to about 2.8J, with the maximum pressures provided by the hospital medical air network (average pressure of 5 bar). Data of the experimental study showed that direct mechanical stimulation (similarly to electric stimulation) can be maintained continuously by five minutes in toad hearts at low heart rate without loss of capture. Nevertheless, the maximum HR during mechanical stimulation before the loss of capture was close to baseline values and significantly lower than during electric stimulation in most toads, possibly because of different types of ion channels activated in mechanical and electrical stimulation. The occurrence of ventricular arrhythmias was similar in both forms of stimulation.