The effects of right atrial and ventricular pacing on the auscultatory findings in patients with mitral valve prolapse.

Abstract

Fifteen patients with midsystolic clicks associated with mitral valve prolapse were studied in order to assess changed in ausculatatory findings produced by pacing-induced variations in cardiac rate, rhythm, and conduction. As the heart rate was increased in stepwise intervals to the maximum possible extent by right atrial pacing (RAP) in 14 patients, the interval between the Q wave and the click (Q-C) decreased in all cases (21 plus or minus msec/10 beats/min; P smaller than 0.001). In two patients, RAP at rates of and above 118 and 159 per minute, respectively, resulted in disappearance of the click. During right ventricular pacing (RVP) without evidence of atrioventricular (A-V) dissociation on the surface ECG in ten patients, the click was inaudible at all pacing rates in three instances. In all seven of the cases in which the click was audible at the lowest rate of RVP with VA conduction, Q-C was greater and C-S2 less than that in sinus rhythm. As the rate of RVP was increased, Q-C was noted to decrease (26 plus or minus 4 msec/10 beats/min) and C-S2 to increase (19 plus or minus 7 msec/10 beats/min) in all patients. In three patients in whom RVP induced atrioventricular dissociation, the click was seen only in beats closely preceded by a P wave. In ten of 11 patients the click occurred earlier in systole with a postextrasystolic or post tachycardia beat as compared to its appearance after a sinus beat when a shorter preceding diastolic filling period was present (P smaller than 0.001). In the eleventh patient a loud systolic murmur was present during a postextrasystolic cycles. It is concluded that pacing-induced rhythm disturbances can result in disappearance of a midsystolic click or can alter its timing and cause it to mimic sonic phenomena seen in other disease states. The possibility of similar changes taking place as a result of spontaneously occurring disturbances of rate, rhythm, and conduction should be recognized in order that the possible diagnosis of mitral valve prolapse not be overlooked.

Effects of gravitational stresses on mitral valve prolapse. I. Changes in auscultatory findings produced by progressive passive head-up tilt.

“…In this patient, however, the click appeared intermittently soon after the adoption of 150 of head-up tilt, and when present was quite loud and late systolic; these findings are not consistent with EDV less than CPV as a cause of absence of a click. During our study of the effect of atrial pacing on click position (Towne et al, 1975), we noted that while in some patients increasing the rate of pacing resulted in fusion of the click with the first sound (Si), in others the click moved toward SI as the rate was increased but became quieter and disappeared in mid-systole. However, this phenomenon was not observed in the patient described here in whom the click was always loud and relatively late when present intermittently at 150 head-up tilt.…”

“…As a result of a study on the effects of atrial and ventricular pacing on click position (Towne et al, 1975), we postulated that there was a critical left ventricular volume at which prolapse occurs for each patient with this condition. If thik were the case, enddiastolic volume, stroke volmne, and ejection rate would be the primary determinants of the presence and timing of a systolic click, and other circulatory factors including preload, heart rate, contractility, and systemic impedance, would be related indirectly to click presence and timing.…”

Mitral valve prolapse.

“…"'7 Infusion of pressor agents is even less practical but results in delay of the click with increased intensity of click and murmur.1 "237 48 Acceleration of heart rate, either spontaneously or due to right atrial or ventricular pacing, serves to decrease left ventricular volume and may cause clicks to move earlier in systole, at times merging with the first heart sound. 49 Careful clinical examination together with the maneuvers SIC S2…”