Midventricular obstruction--a form of hypertrophic obstructive cardiomyopathy--and systolic anterior motion of the mitral valve.

Hypertrophic cardiomyopathy (HCM) has various manifestations with respect to the localization of the hypertrophy. In this study we report clinical, electrocardiographic (ECG), echocardiographic (echo), and hemodynamic findings in midventricular obstruction (MO), an uncommon form of hypertrophic obstructive cardiomyopathy (HOCM) in 9 patients. The prevalence of systolic anterior motion of anterior mitral leaflet (SAM) in MO, an echocardiographic diagnostic hallmark in HOCM, was another purpose of this study. All patients had complete clinical, ECG, echo, and hemodynamic workup, including left ventricular (in 4 patients simultaneous biventricular, SBVA) and coronary angiograms. All patients had dyspnea and palpitations, chest pain, 2 had syncope. In the ECG, atrial fibrillation was present in 2, and left ventricular hypertrophy in 9 patients. Septal and left ventricular free wall thickening was significantly present in all patients in echo, and SAM in 1 patient. The intraventricular gradient (IVG) was 40-176 mmHg, in 1 case 40 mmHg by provocation, Brockenbrough was positive in all patients. Two patients had right ventricular IVG. A positive beta-blocking agent effect was present in 6 cases. The best localization of the obstruction was possible with SBVA and 2D-echo. We conclude that MO has all the signs of HOCM, but SAM in echocardiography is uncommon. SAM is occasionally present and is not a necessary factor to produce an intraventricular pressure gradient in HOCM, especially in MO. It seems that hypertrophic right ventricular obstruction is relatively common in MO (2 of 9 cases), and may have the same obstructive mechanism.