Cardiac mechanical efficiency is preserved in primary cardiac hypertrophy despite impaired mechanical function

Diastolic dysfunction, hypertrophy and hypertension ventricular-arterial uncoupling treatment

The aim of the study was to evaluate hypertension treatment effects on mechanical efficiency of the cardiovascular system and cardiac reverse remodeling in hypertensive patients. This is an observational prospective study, consecutive hypertension patients. Left ventricle mass index measured by Devereux 2D method and diastolic function following the Guidelines from the American Society of Echocardiography and the European Association of Cardiovascular Imaging. Left ventricular end systolic elastance (Ees) was measured by Guarracino calculator, the effective arterial elastance (Ea) and ventricular-arterial coupling (VAC) measured by Sunagawa et al. single beat method adapted by Chen et al. in human ventricles. The sample was analyzed in quartiles (Q) according to VAC. Follow-up 2 years. In total, 288 patients, mean age 56.3 ± 12.5 years and 168 patients (58.3%) males. VAC increased from 0.303 ± 0.07 to 0.54 ± 0.25 (p < 0.005) in Q1 mainly due to a reduction in Ees from 5.25 ± 2.3 to 3.68 ± 0.25 mmHg/ml (p < 0.01), while Ea increased from 1.5 ± 0.53 to 1.64 ± 0.56 mmHg/ml (p = NS). The frequency of LVH was reduced from 31.9 to 10.8% in Q1 (p < 0.025). The frequency of normal diastolic function increased from 75 to 94.6% (p < 0.01) in Q1, from 78.7 to 100% in Q2 (p < 0.005), from 87.1 to 100% (p < 0.025) in Q3 and from 88.7 to 100% (0,025) in Q4. Patients with the worst ventricular-arterial uncoupling were the most benefited from hypertension treatment. Regression of left ventricular hypertrophy was observed only in the group of patients with the worst ventricular-arterial uncoupling, while improvement in diastolic function was demonstrated in all quartiles of patients.

Slower shortening kinetics of cardiac muscle performing Windkessel work‑loops increases mechanical efficiency

Conventional experimental methods for studying cardiac muscle in vitro often do not expose the tissue preparations to a mechanical impedance that resembles the in vivo hemodynamic impedance dictated by the arterial system. That is, the afterload in work‑loop contraction is conventionally simplified to be constant throughout muscle shortening, and at a magnitude arbitrarily defined. This conventional afterload does not capture the time‑varying interaction between the left ventricle and the arterial system. We have developed a contraction protocol for isolated tissue experiments that allows the afterload to be described within a Windkessel framework that captures the mechanics of the large arteries. We aim to compare the energy expenditure of cardiac muscle undergoing the two contraction protocols: conventional versus Windkessel loading. Isolated rat left‑ventricular trabeculae were subjected to the two force-length work‑loop contractions. Mechanical work and heat liberation were assessed, and mechanical efficiency quantified, over wide ranges of afterloads or peripheral resistances. Both extent of shortening and heat output were unchanged between protocols, but peak shortening velocity was 39.0 % lower and peak work output was 21.8 % greater when muscles contracted against the Windkessel afterload than against the conventional isotonic afterload. The greater work led to a 25.2 % greater mechanical efficiency. Our findings demonstrate that the mechanoenergetic performance of cardiac muscles in vitro may have been previously constrained by the conventional, arbitrary, loading method. A Windkessel loading protocol, by contrast, unleashes more cardiac muscle mechanoenergetic potential, where the slower shortening increases efficiency in performing mechanical work.