External Non-invasive Cardiac Pacing: A Comparative Hemodynamic Study of Two Techniques with Conventional Endocardial Pacing

Out-of-hospital therapy for cardiac arrest due to bradyarrhythmias or asystole is pharmacologic and the outcome is uniformly dismal. Optimal therapy for the latter disturbances may be artificial cardiac pacing, but conventional invasive pacing techniques are not employed or are of limited value in the out-of-hospital and emergency department setting. This investigation compared the hemodynamic effects of two techniques of non-invasive external pacing: 1) transcutaneous transthoracic pacing (TTP) and 2) tongue-to-epigastrium pacing (TEP), with conventional transvenous right ventricular endocardial pacing (RVEP) in a closed-chest, chronic heart block canine model. All techniques significantly increased (p less than .001) cardiac output (CO). However, CO and mean arterial pressure (MAP) measured during external pacing with either non-invasive technique were significantly greater than that during RVEP (p less than .001). TEP produced vigorous skeletal muscle stimulation and, in the canine model, it produced contraction resulting in impaired ventilation, hypoxemia, and a decrease in systemic vascular resistance. TTP in this model resulted in improved MAP and CO when compared with control and RVEP values and did not affect arterial or mixed venous blood gas values. Thus, this study demonstrates that noninvasive TTP is comparable to RVEP in its hemodynamic effects. TTP may offer definitive non-invasive therapy for a subset of victims of out-of-hospital cardiac arrest.