Comparison of Half Relaxation Time and Peak Force of Intact Muscle Fibers of Elective CABG Patients with Diastolic Dysfunction Grade I–III

Objectives: Diastolic dysfunction (DD) accounts for more than half of all heart failure patients. The filling of the ventricle during the diastolic phase is caused by muscle relaxation. The force capacity and presence of calcium are the main factors to match the cardiac contraction and velocity of relaxation according to the body’s demands. We therefore examined the force capacity and calcium sensitivity of intact myofilaments of the left (LA) and right (RA) auricle of 83 patients undergoing elective CABG procedure during January 2019 until September 2019.

Methods: LA and RA fibers of 83 elective CABG patients (41 no DD, 42 DD) were harvested in the operation room (13 patients with DD I, 15 patients with DD II, 14 patients with DD III). We recorded force development and relaxation time by exposing intact muscle fibers, which are electrically stimulated (1Hz) to increasing calcium concentrations (Ca++ 0.5 until 2.5 mM). We divided the patients according to the echocardiographic findings of mild, moderate, and severe diastolic dysfunction (E/A, E, E/e′, TR velocity) and compared the half relaxation time (HRT: time taken to the peak twitch to decrease by half its amplitude, ms) of the intact fibers with patients without DD and the peak force (maximal force, mN/mm²).

Results: The HRT of RA and LA intact fibers was not significantly different among patients with DD I and II at calcium concentrations of 0.5 and 2.5 mN. Patients with severe DD showed increased HRT in RA myofilaments when starting the experiment: 168 ± 27 ms versus 148 ms ± 18 ms, p = 0.01 (normal), 128 ± 12 ms, p = 0.003 (mild), and 112 ± 9 ms, p = 0.0001 (moderate). In LA fibers, patients with severe DD had significant increased HRT at 2.5 mM Ca++: 95 ± 12 ms versus 80 ± 7 ms, p = 0.03 (normal), 75 ± 5 ms, p = 0.001 (mild), and 72 ± 9 ms, p = 0.001 (moderate). The peak twitch of LA fibers was significantly decreased (2.02 ± 1.5 mN/mm²) compared to RA fibers (5.60 ± 3.6 mN/mm²) of patients with DD III. No difference existed among the groups DD I and II.

Conclusion: Patients with severe diastolic dysfunction show significant increased half relaxation times compared with other grades of DD, representing the filling impairment. HRT could be decreased when calcium was added due to increased calcium influx. This effect was reversible at highest calcium concentration assuming that calcium might improve the ventricular filling temporarily but is worsening again when calcium saturation is achieved. Maximal values were also significantly reduced in patients with DD III.