Left ventricular shape-based contractility index

Abstract

This study develops contractility indices in terms of the left ventricular (LV) ellipsoidal geometrical shape-factor. The contractility index (CONT1) is given by the maximum value d σ * / d t wherein σ * = σ / P , σ is the wall stress, and σ * is expressed in terms of the shape factor S (the ratio of the minor axis and major axis, B / A , of the instantaneous LV ellipsoidal model). Another contractility index (CONT2) is also developed based on how far apart the in vivo S at the start of ejection is from its optimized value, CONT 2 = ( S se - S se op ) / S se op , where S se refers to the value of S at the start of ejection, S se op is the derived optimal value of S se for which σ* is maximum. The values of S(= B/A) were calculated from cineventriculographically monitored LV volume, myocardial volume and wall-thickness. Then both the contractility indices were evaluated in normal subjects, as well as in patients with mild heart failure and in patients with severe heart failure. The normal values of CONT1 and CONT2 are 8.75±2.30 s −1 and 0.09±0.07, respectively. CONT1 decreased in patients with mild and severe heart failures to 5.78±1.30 and 3.90±1.30, respectively. CONT2 increased in patients with mild and severe heart failures to 0.11±0.09 and 0.23±0.12, respectively. This implies that a non-optimal and less ellipsoidal shape is associated with decreased contractility (and poor systolic function) of the LV. CONT1 and CONT2 are useful as non-invasively determinable quantitative indices of LV contractility, to distinguish between normal and pathologic LVs.