Dissociation between left ventricular untwisting and filling. Accentuation by catecholamines

Area of Science:

• Cardiology
• Physiology
• Biomechanical Engineering

Background:

• Efficient early diastolic filling is crucial for maintaining normal cardiac function.
• Diastolic suction may arise from restoring forces released during systolic deformation and myofilament relaxation.
• Recent evidence suggests gross fiber rearrangement and connective tissue involvement in diastole contribute to stored energy release and suction-aided filling.

Purpose of the Study:

• To precisely determine the timing and extent of left ventricular (LV) torsional deformation restoration relative to early filling.
• To investigate LV untwisting during normal conditions and enhanced relaxation (catecholamine stimulation).

Main Methods:

• Utilized noninvasive magnetic resonance tagging in open-chest dogs to measure LV torsional deformation at 20-msec intervals.
• Quantified epicardial and endocardial circumferential deformations and calculated angular twist.
• Synchronized measurements with Echo-Doppler to determine aortic and mitral valve timing.

Main Results:

• LV torsion rapidly reversed during isovolumic relaxation, before mitral valve opening.
• Untwisting occurred without significant concurrent circumferential segment lengthening.
• Catecholamine stimulation (dobutamine) significantly increased end-systolic torsion and accelerated/magnified the reversal during isovolumic relaxation.

Conclusions:

• LV untwisting primarily occurs during isovolumic relaxation, preceding ventricular filling.
• This reversal of systolic deformation releases potential energy stored in myocardial elastic elements.
• Enhanced untwisting by catecholamines, as seen during exercise, may compensate for shortened filling times.