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CLINICAL STUDY: HYPERTROPHIC CARDIOMYOPATHY

Echocardiographic insights into the mechanisms of relief of left ventricular outflow tract obstruction after nonsurgical septal reduction therapy in patients with hypertrophic obstructive cardiomyopathy

^a Department of Medicine, Cardiology Section, Baylor College of Medicine, Houston, Texas, USA

Manuscript received March 3, 2000; revised manuscript received July 24, 2000, accepted September 11, 2000.

Reprint requests and correspondence: Dr. Sherif F. Nagueh, Cardiology Section, 6550 Fannin Street, SM-1246, Houston, Texas 77030
sherifn{at}bcm.tmc.edu

OBJECTIVES

We sought to evaluate the mechanisms by which nonsurgical septal reduction therapy (NSRT) reduces left ventricular outflow tract (LVOT) obstruction in patients with hypertrophic obstructive cardiomyopathy (HOCM) both acutely and on a long-term basis.

BACKGROUND

NSRT reduces LVOT obstruction in patients with HOCM and leads to symptomatic improvement. The mechanisms involved, however, are not well studied.

METHODS

An initial group of 30 HOCM patients (age 46 ± 17, 16 women) who underwent NSRT had echocardiographic studies performed at baseline and six months after the procedure. Measurements included LVOT diameter, end-diastolic distance between the anterior mitral leaflet and interventricular septum, septal base function and the angle between LV systolic flow and the protruding mitral leaflets. In addition, pulse Doppler recordings at a point 2.5 cm apical to the mitral valve were acquired and analyzed for peak and mean ejection velocity, peak acceleration rate and the ratio of acceleration time to ejection time (AT/ET).

RESULTS

Significant changes were observed after the procedure, with widening in the LVOT, thinning and akinesis of the septal base, decrease in the angle between LV systolic flow and the protruding mitral leaflets, a decrease in peak acceleration rate and an increase in AT/ET. All of these variables had significant relations with the decrease in LVOT obstruction (r = 0.5 to 0.79, p < 0.01). These correlations were then evaluated in a test group of 15 patients who underwent echocardiographic examinations at baseline, acutely in the catheterization laboratory with ethanol injection and at six weeks post NSRT. Acute changes in peak acceleration rate (r = 0.65) and AT/ET (r = 0.73) related significantly (p < 0.01) to the decrease in LVOT obstruction with ethanol. At six weeks, changes similar to those noted in the initial group were observed in LVOT geometry, the angle between LV systolic flow and the protruding mitral leaflets, peak acceleration rate and AT/ET. In both populations combined, these parameters accounted for 72% to 77% of the variance in gradient reduction.

CONCLUSIONS

Changes in LV ejection dynamics and septal base function account in part for the acute relief of LVOT gradient after NSRT. The long-term relief of obstruction is dependent on remodeling of LVOT as well as the changes in LV ejection.

Abbreviations and Acronyms   AML = anterior mitral leaflet   AT = acceleration time   ET = ejection time   HOCM = hypertrophic obstructive cardiomyopathy   LA = left atrial   LVOT = left ventricular outflow tract   MR = mitral regurgitation   NSRT = nonsurgical septal reduction therapy   SAM = systolic anterior motion

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