Left ventricular geometry in normal and post-anterior myocardial infarction patients: sphericity index and 'new' conicity index comparisons.

Background: Anterior myocardial infarction leads a sequence of structural changes that alter the size and the shape of the left ventricle. Efforts to assess shape have been made by global left ventricular (LV) chamber analysis (sphericity index, SI) but this analysis does not detect regional shape abnormalities like those at the apical level, which precede global ventricular dilatation.

Objective: The present study will introduce a new analysis of regional apical changes in 52 normal subjects and in 92 patients with previous anterior myocardial infarction.

Methods: All patients had transthoracic echocardiogram and multiple views were obtained (long axis, 4CH, 2CH and short axis view). From the 4CH view the long and the short axes were measured and their ratio was calculated (sphericity index). In the same view, the apical axis length was also measured and the ratio between apical and short axis length was calculated (apical conicity index, ACI).

Results: Patients had all the measured parameters significantly worse than normal, except the sphericity index which remained unchanged. Ventricular length and width increased following anterior MI but the ratio between the two measurements did not change. Conversely, apical conicity index is significantly different following anterior MI, thereby indicating anterior infarction produces a less conical shape. SI and ACI differed when correlations were made in the relationship of mitral valve function; SI correlates with the degree of mitral regurgitation (MR) and with the distance of papillary muscles, conversely ACI shows an inverse correlation with the determinants of mitral regurgitation. These observations reflect differences between apical versus global dilatation in ischemic cardiomyopathy, so that mitral function is better (lower tenting area and lower coaptation height) when the apex is markedly dilated in respect to the short axis (high conicity index). In contrast, mitral function is impaired (bigger distance between papillary muscles and higher degree of mitral regurgitation), when sphericity index is high.

Conclusions: Sphericity index fails to detect regional apical shape abnormalities. To address this focal change, we introduce a simple new measure termed apical conicity index, which is abnormal in patients with myocardial infarction, and can be useful to evaluate changes induced by the subsequent surgical approach of ventricular re-shaping.