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The Effects of Ventricular Pacing on Left Ventricular Geometry, Function, Myocardial Oxygen Consumption, and Efficiency of Contraction in Conscious Dogs
Author(s) -
OWEN CLARENCE H.,
ESPOSITO DAVID J.,
DAVIS JAMES W.,
GLOWER DONALD D.
Publication year - 1998
Publication title -
pacing and clinical electrophysiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.686
H-Index - 101
eISSN - 1540-8159
pISSN - 0147-8389
DOI - 10.1111/j.1540-8159.1998.tb00213.x
Subject(s) - medicine , preload , sonomicrometry , cardiology , ventricular pacing , stroke volume , fissipedia , hemodynamics , anesthesia , ejection fraction , heart failure
The effects of ventricular pacing on left ventricular (LV) dynamic geometry, function, and myocardial oxygen consumption (MVO 2 ) were measured in 12 conscious dogs using sonomicrometry, micromanometry, ultrasonic flow probes, and oximetry catheters during right atrial (A‐) and right ventricular (V‐) pacing at 150 beats/mm. Systolic function was quantified using slopes (M w ) and volume‐intercepts (V w ) of linear relationships between end‐di‐astolic volume (EDV) and stroke work (SW) for data obtained during vena caval occlusion. V‐pacing shifted SW‐EDV relationships downward (M w decreased from 97 ± 21 to 81 ± 21 Kerg/mL) and to the right (V w increased from 14 ± 11 to 20 ± 12 mL) in comparison with A‐pacing (P < 0.05). These functional changes correlated with altered contractile geometry manifest as early shortening in the septal free wall relative to anterior‐posterior dimension (increased minor axis mid‐wall eccentricity at end‐diastole and begin‐ejection). Steady‐state LV power output decreased from 802 ± 213 mW during A‐pacing to 514 ± 170 mW during V‐pacing (P < 0.05), while MVO 2 remained relatively unchanged during V‐pacing (10 ± 3 mL O 2 /min vs 11 ± 3 mL O 2 /min during A‐pacing, P = NS). As a result, overall LV efficiency decreased from 0.24 ± 0.08 during A‐pacing to 0.16 ± 0.06 during V‐pacing (P < 0.05). These data illustrate the impact of V‐pacing on dynamic LV geometry and function, including impaired LV work output at all physiological levels of preload. Most importantly, the relationship between LV work output and MVO 2 is depressed during V‐pacing, emphasizing the interaction between LV mechanics and pump efficiency in intact subjects. As a result, measures taken to restore normal contractile geometry might improve LV efficiency and performance when V‐pacing is necessary.