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Diastolic mechanisms of impaired exercise tolerance in aortic valve disease
Insights
Exercise echocardiography reveals abnormal left ventricular filling in patients with left ventricular hypertrophy. These abnormalities, particularly evident at higher heart rates, indicate a loss of normal diastolic filling mechanisms.
Area of Science:
- Cardiology
- Physiology
- Echocardiography
Background:
- Left ventricular hypertrophy (LVH) can impact cardiac function.
- Diastolic dysfunction is a key concern in LVH.
- Exercise stress testing is crucial for uncovering functional limitations.
Purpose of the Study:
- To investigate diastolic function abnormalities during exercise in patients with LVH.
- To compare exercise-induced diastolic changes between normal subjects and LVH patients.
- To identify specific echocardiographic markers of diastolic dysfunction in LVH.
Main Methods:
- Exercise echocardiography performed to 140-150 beats/min in 18 normal subjects and 14 patients post-aortic valve replacement with LVH.
- Simultaneous ECG, phonocardiograms, and echocardiograms recorded.
- Measurements included left ventricular dimensions, mitral valve timing, filling time, isovolumic relaxation time, and systolic function parameters.
Main Results:
- Patients with LVH showed prolonged isovolumic relaxation at rest (85 ms vs. 69 ms).
- Normal subjects exhibited a significant drop in filling time with exercise (380 ms/beat to 115 ms/beat).
- LVH patients' filling times did not decrease with exercise (367 ms/beat to 240 ms/beat), showing preserved filling at higher rates, distinguishing them from controls above 120 beats/min.
Conclusions:
- Exercise echocardiography effectively demonstrates significant left ventricular filling abnormalities in LVH patients.
- These abnormalities suggest a loss of normal mechanisms for rapid diastolic filling during exertion.
- Abnormal diastolic function during exercise is a key finding in patients with left ventricular hypertrophy.
Abstract:
In order to determine the significance of abnormalities of diastolic function in patients with left ventricular hypertrophy, exercise echocardiography to heart rates of 140 to 150 beats/min was performed in 18 normal subjects and 14 patients after aortic valve replacement. Simultaneous echo-, phono-, and electrocardiograms were recorded. Left ventricular cavity size was determined at end-diastole and end-systole. The timing of mitral valve opening and closure was measured, and hence left ventricular filling time derived, expressed either as ms/beat, or s/min when multiplied by heart rate. Isovolumic relaxation was taken as the interval between A2 and mitral valve opening. Systolic function, assessed from cavity dimensions, peak VCF, and QA2 interval was normal in all but two patients at rest and on exercise. Isovolumic relaxation was prolonged at rest in the patients to 85 +/- 8 ms (normal 69 +/- 9 ms), but left ventricular filling times were normal. With exercise, in normal subjects, isovolumic relaxation remained constant, but filling times dropped strikingly from 380 +/- 66 ms/beat, or 27 +/- 2 s/min at rest to 115 +/- 10 ms/beat or 16 +/- 2 s/min. In patients with left ventricular hypertrophy, isovolumic relaxation dropped on exercise to 41 +/- 15 ms. Filling periods were normal at rest, 367 +/- 67 ms/beat or 27 +/- 3 s/min, but failed to show the normal drop with exercise, being 240 +/- 44 ms/beat or 28 +/- 4 s/min. At heart rates above 120/min, separation between the two groups was complete. Thus, striking abnormalities of left ventricular filling can be demonstrated on exercise in patients with left ventricular hypertrophy. They appear to represent loss of mechanisms whereby rapid diastolic filling is achieved in the normal subject.