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Spontaneous variability of left ventricular outflow tract gradient in hypertrophic obstructive cardiomyopathy
A M Kizilbash1, S K Heinle, P A Grayburn
1Department of Internal Medicine, University of Texas Southwestern Medical School and VA Medical Center, Dallas 75235-9047, USA.
Insights
The left ventricular outflow tract (LVOT) gradient in hypertrophic obstructive cardiomyopathy (HOCM) patients varies significantly day-to-day. A single LVOT gradient measurement is insufficient for assessing HOCM obstruction severity.
Area of Science:
- Cardiology
- Medical Diagnostics
- Hemodynamics
Background:
- Left ventricular outflow tract (LVOT) gradient assessment is crucial for evaluating treatment response in hypertrophic obstructive cardiomyopathy (HOCM).
- Limited data exist on the spontaneous day-to-day variability of LVOT gradient in HOCM patients.
- Understanding this variability is key to accurately interpreting therapeutic effects on LVOT obstruction.
Purpose of the Study:
- To quantify the spontaneous day-to-day variability of the LVOT pressure gradient in HOCM patients.
- To determine if physiological factors or technical issues explain this variability.
- To establish a reliable threshold for therapeutic change in LVOT gradient.
Main Methods:
- Continuous-wave Doppler-derived pressure gradients were measured over 5 consecutive days in 12 HOCM patients.
- Measurements included resting and provoked gradients.
- Control group of 5 aortic stenosis patients were studied for comparison; physiological parameters were monitored.
Main Results:
- Significant day-to-day variability in LVOT gradient was observed in HOCM patients.
- The 95% confidence interval for non-random variation was +/-32 mm Hg (resting) and +/-50 mm Hg (provoked).
- Variability was not explained by changes in heart rate, blood pressure, or LV end-diastolic dimension; technical factors were ruled out.
Conclusions:
- The LVOT pressure gradient exhibits considerable day-to-day fluctuation in stable HOCM patients.
- A single LVOT gradient measurement is inadequate for defining the severity of dynamic obstruction in HOCM.
- Serial measurements are necessary for accurate assessment of HOCM obstruction.
Background:
Improvement in the left ventricular outflow tract (LVOT) gradient has been used as a means of assessing response to therapy in patients with hypertrophic obstructive cardiomyopathy (HOCM). To our knowledge, no data exist regarding the spontaneous day-to-day variability of the LVOT gradient in patients with HOCM. Defining the magnitude of such variability is critical to properly understand how much improvement in LVOT gradient must be present to invoke a therapeutic response.
Methods And Results:
We studied the spontaneous variation in the continuous-wave, Doppler-derived pressure gradient on 5 consecutive days in 12 HOCM patients and 5 aortic stenosis control subjects. While in some patients the day-to-day variability in resting gradient was small, in others it varied markedly. The 95% confidence interval for attributing a change in LVOT gradient to factors other than random variation is +/-32 mm Hg for resting gradient and +/-50 mm Hg for provoked gradient. The mean coefficient of variation for gradient across 5 days for the group was 0.52+/-0.33 for resting gradient and 0.46+/-0.16 for provoked gradient. The day-to-day variability in pressure gradient could not be explained by changes in heart rate, blood pressure, or left ventricular end-diastolic dimension, each of which had a coefficient of variation <.11. Moreover, technical factors related to the performance or interpretation of the studies did not account for it because the coefficient of variation for gradient in aortic stenosis was <10% and interobserver and intraobserver agreement was excellent (r=.96 and .98, respectively).
Conclusions:
The LVOT pressure gradient varies considerably from day to day in stable patients with HOCM. A single measurement of pressure gradient is not adequate to define the severity of dynamic LVOT obstruction in HOCM.