Purpose. Recent studies have demonstrated that ventricular rate control is a viable treatment strategy for patients in atrial fibrillation (AF). The purpose of this study was to determine whether or not the benefits of coupled pacing (ie, a proposed rate control therapy) could be used during persistent AF.
Description. Six mongrel dogs were chronically implanted with endocardial atrial and ventricular pacemaker leads and two standard dual-chamber pacemakers. With the use of two custom "Y"-lead adapters, the pacemakers were used to induce AF and to apply coupled pacing. Left ventricular end-diastolic and systolic volumes were measured by echocardiography to determine ejection fractions.
Evaluation. Persistent AF significantly increased both ventricular rate and left ventricular dimensions. After sustained coupled pacing had been applied for 3 to 4 weeks, left ventricular volumes and contractile rate were significantly reduced and returned toward the values measured prior to the induction of persistent AF. Coupled pacing increased the ejection fraction that had been reduced by persistent AF.
Conclusions. Coupled pacing reversed the left ventricular remodeling caused by the tachycardia resulting from AF.
For the last several years, our laboratory has been investigating the implementation of coupled pacing (CP) (a novel pacing paradigm) for controlling the ventricular rate of mechanical contraction (VRMC). Using CP involves the application of electrical stimuli to the ventricles after the effective refractory period. In previous studies [1-3], we reported that acute application of CP resulted in both a negative chronotropic (mechanical not electrical rate) and a positive inotropic response during acutely induced atrial fibrillation (AF). Reduction in ventricular contractions by CP is the result of blocked conduction of rapid supraventricular activations to the ventricles during AF. When CP slowed this ventricular rate of contraction, stroke volume increased markedly as a result of moderate increases in left ventricular enddiastolic volume and the decrease in end-systolic volume [1, 3]. In addition, the positive inotropic effects of CP (resulting from postextrasystolic potentiation) increased left ventricular (LV) first derivative of left ventricular pressure (dp/dt) and LV ejection fraction (EF). The purpose of this study was to determine if sustained CP could be used in the setting of persistent AF.
All animals used in this study received humane care in compliance with the "Guide for the Care and Use of Laboratory Animals" published by National Institutes of Health. Six mongrel dogs (20 to 30 kg) were included in this study.
During echocardiographic imaging, all pacemakers were temporarily turned off to assess cardiac function, except during CP therapy. Echocardiographic data were acquired (Sequoia, with a 3-MHz probe [Seimens System, Mountain View, CA]) at (1) baseline during sinus rhythm, (2) after persistent AF, but just before the beginning of CP therapy, and (3) after 3 to 4 weeks of continual application of CP. Left ventricular end-diastolic volume (LVEDV) and left ventricular end-systolic volume (LVESV), as well as left atrial volumes (LAV) (measured at end systole of the left ventricle), were computed from standard apical views (ie, 2-chamber view and 4-chamber view) by using the Simpson bi-plane method. Left ventricular EF was calculated from these measurements ([LVEDV - LVESV]/ LVEDV). Measurements from three cardiac cycles as defined by visible contractions were averaged for all volumes, and these mean values were expressed as a single value.
Dr. George Yanulis is a broadly experienced Medical Device Engineer with a Doctorate in Engineering in Biomedical Engineering (D.Eng), a proven research and development background and experience collaborating with basic scientists and clinicians in cardiac electrophysiology, teaching and mentoring both undergraduate and graduate students in biomedical engineering and related disciplines.
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