[Noninvasive studies of dynamic left ventricular outflow obstruction in patients with sigmoid septum]

In order to evaluate the clinical significance of the markedly protruding interventricular septum into the left ventricular (LV) cavity (sigmoid septum), we performed non-invasive studies including amyl nitrite (AN) inhalation in 21 patients (pts) with two-dimensional echocardiographic (2DE) documentations. LV outflow tract (LVOT) obstruction was determined by the presence at least three of the following findings at rest or during AN inhalation: 1) a loud apical ejection systolic murmur (ESM), 2) a midsystolic dip in the carotid pulse, 3) systolic anterior motion (SAM) of the mitral valve (MV) or chordae tendineae, and 4) systolic semiclosure of the aortic valve (AV). The 21 pts were subdivided into six pts (group I) with resting (two pts) or provocative (four) obstruction, and 15 pts (group II) without obstruction. Their ages ranged from 40 to 85 years with an average of 65. No pt had evidence of hypertrophic cardiomyopathy. Results were as follows: In five pts of group I a long ESM with a mid-systolic peak was recorded near the apex. After AN inhalation, this murmur was markedly intensified. On the contrary, all pts of group II had a short and early systolic murmur, which was not markedly intensified by AN. In contrast to group II, group I pts had a significantly smaller LV end-diastolic dimension, a smaller LVOT dimension, higher percent thickening of the LV posterior wall, higher fractional shortening and decreased aorto septal angle (the angle between the anterior aortic wall and the interventricular septum by 2DE). On 2DE, each pt of group I showed significant narrowing between the protruded septum and the hypercontractile LV posterior wall with the papillary muscle. Anteriorly shifted chordae tendineae noted as the SAM on the M-mode echocardiogram might also play an important role on the genesis of obstruction. The signs of LVOT obstruction at rest disappeared following oral administration of propranolol in two pts of group I. These observations suggested that LVOT obstruction might occur in some pts with sigmoid septum and the hypercontractile state, and that a systolic murmur observed in this condition should be differentiated from a functional murmur in the aged or a systolic murmur in hypertrophic obstructive cardiomyopathy.