Regional myocardial work: a new method to assess local myocardial function

The aim of this study was the assessment of the regional myocardial work (RMW) by measuring the stress-strain relationships in the left myocardium, under basic and ischemic conditions. In 11 swines, 4 sonometrics crystals were placed in the region perfused by the left anterior descending artery (LAD) circumscribing a tetrahedral myocardial volume (TMV). The 1st crystal was situated 45 mm below the pulmonary artery, beside the LAD. Under control of the acquisition device, the 2nd was placed 10 mm below the 1st following the LAD, the 3rd 10 mm at the left side of the 1st and the 4th in equidistant point between the 1st and the 2nd, 5 mm deep within the myocardium. A Millar, omnidirectional pressure catheter was placed within the TMV. The 6 distances and intramyocardial pressure measured were digitized and mathematically synthesized. The variation in TMV strain (muv) and stress (mup) was calculated throughout the cardiac cycle, resulting in 2 equations. The relationships between mup and muv result in a stress-strain loop, from which RMW was calculated. Simultaneously, pulsed Doppler tissue imaging (DTI) assessed systolic (VS), early-diastolic (VE) and late-diastolic (VA) myocardial velocities. Measurements were performed under basic (B), during ischemia by occlusion LDA for 40 seconds, after 1 and 15 minutes of reperfusion (occlusion (O), reperfusion1 (R1) and 2 (R2) periods). The average of RMW, under basic conditions, was 0.679plusmn0.025 mJ. While DTI,VS:0.09plusmn0.03 ms-1; VE:-0.10plusmn0.03 ms-1; VA:-0.08plusmn0.04 ms-1; VE/VA:1.4plusmn0.6 ms-1. RMW significantly decreased during occlusion: 0.042plusmn0.005 (P<0.05) mJ, and recovered partially in reperfusion1: 0.212plusmn0.015 (P<0.05) mJ, and was increased in reperfusion2: 0.928plusmn0.029 (P<0.05) mJ. In contrast, DTI shows a decrease of velocities in occlusion, VS: 0.06plusmn0.01 (P<0.05) ms-1; VE:-0.06plusmn0.03 (P<0.05) ms-1; VA:-0.08plusmn0.02 ms-1; VE/VA:1.04plusmn0.3 ms-1 and did not s- - ignificantly vary in reperfusion periods. The RMW quantifies the regional myocardial function, showing a decrease under ischemic condition and complete recovery in reperfusion. While DTI failed to demonstrate recovery in reperfusion, RMW appears more accurate than DTI in the assessment of the regional myocardial function and may be used in the evaluation of heart function under basic and pathological conditions