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

OBJECTIVES We sought to evaluate the mechanisms by which nonsurgical septal reduction therapy (NSRT) reduces left ventricular outflow tract (LVOT) obs truction in patients with hypertrophic obstructive cardiomyopathy (HOCM) bo th 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 st udied. 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-diasto lic distance between the anterior mitral leaflet and interventricular septu m, septal base function and the angle between LV systolic flow and the prot ruding 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 mea n ejection velocity, peak acceleration rate and the ratio of acceleration t ime to ejection time (AT/ET). RESULTS Significant changes were observed after the procedure, with widenin g in the LVOT, thinning and akinesis of the septal base, decrease in the an gle between LV systolic dow 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, acut ely in the catheterization laboratory with ethanol injection and at six wee ks 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 obstruc tion with ethanol. At six weeks, changes similar to those noted in the init ial group were observed in LVOT geometry, the angle between LV systolic flo w 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 accoun t in part for the acute relief of LVOT gradient after NSRT. The long-term r elief of obstruction is dependent on remodeling of LVOT as well as the chan ges in LV ejection. (J Am Cell Cardiol 2001;37: 208-14) (C) 2001 by the Ame rican College of Cardiology.