Improved Left Ventricular Relaxation During Short-term Right Ventricular Outflow Tract Compared to Apical Pacing* Theofilos M. Kolettis, MD; Zenon S. Kyriakides, MD; Dimitrios Tsiapras, MD; Todor Popov, MSc; Ioannis A. Paraskevaides, MD; Dimitrios Th. Kremastinos, MD Study objectives: Pacing-induced asynchrony may deteriorate left ventricular function; however, limited data exists in humans. The aim of our study was to compare left ventricular hemodynamics during short-term atrioventricular sequential pacing from the right ventricular apex and from the outflow tract of the right ventricle. Design: Three 5-min pacing intervals were applied in a random order, at a rate of 15 beats/min above the resting sinus rate. Atrioventricular sequential pacing from the two sites was compared with atrial pacing. During each pacing mode, left ventricular pressure was recorded, and cardiac output was calculated using Doppler echocardiography. Setting: Cardiac catheterization laboratory. Patients: Twenty patients (18 male, mean age 62  11 years) without structural heart disease were studied. Results: During atrial pacing, maximum negative first derivative of pressure (dp/dt) was 1,535  228 mm Hg/s; during pacing from the apex it decreased to 1,221  294 mm Hg/s (p  0.0001), but was not significantly different during pacing from the outflow tract (1,431  435 mm Hg/s, p > 0.05). Isovolumic relaxation time constant () during atrial pacing was 39.7  11.9 ms; during pacing from the apex, it increased to 47.9  14.0 (p  0.001), but was not significantly different during pacing from the outflow tract (42.5  11.2, p > 0.05). Peak systolic pressure decreased significantly during atrioventricular sequential pacing from either site; however, it did not differ between the two sites. No differences in end-diastolic pressure, maximum positive dp/dt, or cardiac output could be demonstrated. Conclusion: In patients with no structural heart disease, short-term right ventricular outflow tract pacing is associated with more favorable diastolic function, compared to right ventricular apical pacing. (CHEST 2000; 117:60 – 64) Key words: apex; diastolic function; hemodynamics; outflow tract; pacing Abbreviations: AAI = atrial pacing; DDD = atrioventricular dual-chamber sequential pacing; dp/dt = first derivative of pressure; SP = peak systolic pressure; = isovolumic relaxation time constant S ince the introduction of permanent pacing, the preferred site for ventricular stimulation has been almost exclusively the right ventricular apex, because this site provides excellent lead stability and low capture thresholds. However, such pacing results in an asynchronous ventricular contraction, associated with a deterioration in left ventricular systolic and diastolic function indexes. 1,2 Pacing from the right ventricular outflow tract mimics the normal ventric- ular activation sequence, decreases the degree of pacing-induced asynchrony, and may produce less deterioration in left ventricular performance. 3 How- ever, there are no detailed hemodynamic data in humans with regard to atrioventricular dual-cham- ber sequential pacing (DDD) from the two sites. The purpose of our study was to compare the acute hemodynamic status during short-term DDD pacing from the apex vs the outflow tract of the right ventricle in patients with no structural heart disease. Materials and Methods Participants in our study were screened among patients re- ferred for diagnostic cardiac catheterization and electrophysi- *From the 2nd Department of Cardiology, Onassis Cardiac Surgery Center, Athens, Greece. Manuscript received December 23, 1998; revision accepted July 15, 1999. Correspondence to: Theofilos M. Kolettis, MD, Onassis Cardiac Surgery Center, 356 Syngrou Ave, 176 74 Kallithea, Athens, Greece; e-mail: elbee@ath.forthnet.gr 60 Clinical Investigations Downloaded From: http://journal.publications.chestnet.org/pdfaccess.ashx?url=/data/journals/chest/21938/ on 06/25/2017