Enhanced ventricular untwisting during exercise - A mechanistic manifestation of elastic recoil described by doppler tissue imaging

Background - The cascade of events by which early diastolic left ventricular (LV) filling increases with exercise is not fully elucidated. Doppler tissue imaging (DTI) can detect myocardial motion, including torsion, whereas color M-mode Doppler (CMM) can quantify LV intraventricular pressure gradients (IVPGs). Methods and Results - Twenty healthy volunteers underwent echocardiographic examination with DTI at rest and during submaximal supine bicycle exercise. We assessed LV long-/short-axis function, torsion, volume, inflow dynamics, and early diastolic IVPG derived from CMM data. LV torsion and untwisting velocity increased with exercise (torsion, 11 +/- 4 degrees to 24 +/- 8 degrees; untwisting velocity, -2.0 +/- 0.7 to -5.6 +/- 2.3 rad/s) that was associated with an increase in IVPG (1.4 +/- 0.5 to 3.7 +/- 1.2 mm Hg). Untwisting in normal subjects occurred during isovolumic relaxation and early filling, significantly before long-axis lengthening or radial expansion. The clinical feasibility of this method was tested in 7 patients with hypertrophic cardiomyopathy (HCM); torsion was higher at rest but did not increase with exercise (16 +/- 4 degrees to 14 +/- 6 degrees), whereas untwisting was delayed and unenhanced (-1.6 +/- 0.8 to -2.3 +/- 1.2 rad/s). In concert, IVPG was similar at rest (1.2 +/- 0.3 mm Hg), but the exercise response was blunted (1.6 +/- 0.8 mm Hg). In normal subjects and HCM patients, there was a similar linear relation between IVPG and untwisting rate, with an overall correlation coefficient of r = 0.75 (P < 0.0001). Conclusions - LV untwisting appears to be linked temporally with early diastolic base-to-apex pressure gradients, enhanced by exercise, which may assist efficient LV filling, an effect that appears blunted in HCM. Thus, LV torsion and subsequent rapid untwisting appear to be manifestations of elastic recoil, critically linking systolic contraction to diastolic filling.