Importance of the “atrial kick” in determining the effective mitral valve orifice area in mitral stenosis

Abstract

Atrial fibrillation with a rapid ventricular response in patients with mitral stenosis (MS) is often accompanied by pulmonary congestion and reduced cardiac output owing to a diminished diastolic filling period and the loss of the end-diastolic left ventricular (LV) pressure increment. To test the hypothesis that loss of atrial contraction (atrial kick) also results in a decrease in effective mitral valve orifice area, 6 patients with pure, isolated MS were studied in sinus rhythm during atrial pacing and simultaneous atrioventricular pacing. Atrial pacing at 140 beats/min caused no significant change from baseline in cardiac output or mitral valve area, but there was a decrease in LV end-diastolic volume and ejection fraction as well as an increase in left atrial pressure and mean diastolic gradient. Simultaneous atrioventricular pacing (to eliminate atrial kick) induced a decrease in cardiac output (4.4 ± 0.9 vs 5.2 ± 0.8 liters/min at 110 beats/min, 4.2 ± 0.9 vs 5.1 ± 0.9 liters/min at 140 beats/min; p < 0.05) and LV end-diastolic volume (77 ± 27 vs 93 ± 29 ml at 110 beats/min, 54 ± 17 vs 65 ± 19 ml at 140 beats/min; p < 0.05), an increase in left atrial pressure (28 ± 3 vs 20 ± 5 mm Hg at 110 beats/min, 30 ± 4 vs 25 ± 5 mm Hg at 140 beats/min; p < 0.05), and a decrease in mitral valve area (1.2 ± 0.4 vs 1.4 ± 0.5 cm 2 at 110 beats/min, 1.2 ± 0.4 vs 1.4 ± 0.4 cm 2 at 140 beats/min; p < 0.05). Thus, loss of atrial kick may cause pulmonary congestion and reduced cardiac output in patients with MS, partly because of a decrease in effective mitral valve area.