Physiologic mechanisms in aortic insufficiency. I. The effect of changing heart rate on flow dynamics. II. Determinants of Austin Flint murmur.

Abstract

SUMMARY We studied the dynamic changes in mitral flow patterns and in mitral valve motion before and after producing acute, reversible aortic insufficiency (Al) in nine open-chest dogs. Phasic mitral flow, the mitral valve echocardiogram, the intracardiac phonocardiogram and other hemodynamic variables were measured. During moderate Al (mean regurgitant fraction 52 ± 5%) (± SD), the antegrade filling volume decreased from 31 ± 7 to 24 ± 6 ml (p < 0.01), but the peak protodiastolic mitral flow rate increased from 139 ± 37 to 157 ± 42 ml/sec (p < 0.01), reflecting the shift of a larger fraction of total mitral filling volume to early diastole. In six dogs, atrial pacing was used to examine the hemodynamic effects of tachycardia. Increasing the heart rate from 90 to 120 beats/min increased cardiac output from 2.64 ± 0.56 to 3.3 ± 0.831/min (p < 0.05) and decreased left atrial pressure from 24 ± 8 to 17 ± 7 mm Hg (p < 0.05).Increasing heart rate to 150 beats/min compromised mitral filling, reduced cardiac output and increased left atrial pressure. Moderate tachycardia improves cardiac performance in Al by reducing regurgitant volume, without significantly reducing transmitral filling volume. The mitral valve echocardiogram showed only a small decrease in cusp opening amplitude during Al. A low-pitched left ventricular inflow tract murmur was recorded in protodiastole and corresponded in time to the rapidly increasing mitral flow. We conclude that the major determinant of the turbulence responsible for the creation of the Austin Flint murmur is the antegrade mitral flow stream and its mixing with the retrograde aortic flow.THE PATHOPHYSIOLOGY, clinical recognition and management of aortic insufficiency (Al) have been studied extensively in recent years. Clinical expressions of chronic and acute aortic regurgitation have been well defined,' and data regarding the natural history of the disease2' 3 and the proper selection of patients for medical vs surgical treatment is rapidly accumulating.f7 However, little is known about the dynamics of atrioventricular diastolic flow transport and, hence, about the significance of alterations in diastolic left ventricular (LV) filling in Al. To compensate for the immediate decrease in effective flow, Al may rapidly activate other physiologic mechanisms in addition to the Starling mechanism. Tachycardia is of particular benefit to patients with chronic or acute Al,8 although the mechanism by which increased heart rate (HR) specifically favors the hemodynamics of A! is not clear.9-12We undertook the present study to investigate the dynamic changes that occur on the left side of the heart with the onset of acute Al. Using our established technique of simultaneous phasic mitral flow and echocardiographic measurements, we placed particular emphasis on LV filling and mitral valve motion during the different phases of diastole. We concentrated on two aspects of mitral flow: the mechanism by which moderate increases in HR affect mitral and aortic flow to improve LV pump function, and th...

Impact of restrictive physiology on intrinsic diastolic right ventricular function and lusitropy in children and adolescents after repair of tetralogy of Fallot

“…In addition to diastolic properties and the afterload of the RV, the RV diastolic filling time also may play a role 21. Previous studies in dogs showed that an increased heart rate was associated with a decrease in aortic regurgitation due to the shortening of diastole 22. The present results confirm these findings for the RV performance as well, suggesting that the observed changes in pulmonary regurgitation are also due to increased heart rates with consecutively abbreviated diastole.…”

Cardiovascular response to dynamic exercise in patients with chronic symptomatic mild-to-moderate and severe aortic regurgitation.

“…Although there is a decrease in the duration of diastole with increased heart rate and a decrease in RgV/beat, the forward stroke volume also decreases with atrial pacing, and no change or fall in mean arterial or PAWP is seen. 12 At rest, the ejection fraction for the patients with mild-to-moderate AR was normal, while it was decreased below 0.50 in five of the nine patients with severe AR. With exercise, although a significant increase occured for the group, the individual responses were variable and the direction and magnitude of change was not related to the resting ejection fraction or the severity of the AR.…”

Doppler and echocardiographic characteristics of patients having an Austin Flint murmur.

“…The presence of a diastolic left ventricular-left atrial gradient, while associated with diastolic mitral insufficiency, was not associated with an Austin Flint murmur.12 A more recent animal study using mitral and aortic flowmeters further demonstrated that forward mitral flow and regurgitant aortic flow were always simultaneously present when an Austin Flint murmur was produced. 13 In summary, the mechanism of production of the Austin Flint murmur is still uncertain. Prior work has established that 1) the sound of the murmur probably originates from the left ventricular inflow tract, 12 2) the mitral valve must be open and hence, forward flow across the valve is necessary," and 3) significant aortic insufficiency must be present.2'10-'2 '14 However, not all patients with significant aortic insufficiency have an audible Austin Flint murmur.…”