Left Ventricular Rotation and Twist Assessed by Four-Dimensional Speckle Tracking Echocardiography in Healthy Subjects and Pathological Remodeling: a Single Center Experience

In silico investigation of the short QT syndrome, using human ventricle models incorporating electromechanical coupling

INTRODUCTION

Genetic forms of the Short QT Syndrome (SQTS) arise due to cardiac ion channel mutations leading to accelerated ventricular repolarization, arrhythmias and sudden cardiac death. Results from experimental and simulation studies suggest that changes to refractoriness and tissue vulnerability produce a substrate favorable to re-entry. Potential electromechanical consequences of the SQTS are less well-understood. The aim of this study was to utilize electromechanically coupled human ventricle models to explore electromechanical consequences of the SQTS.

METHODS AND RESULTS

The Rice et al. mechanical model was coupled to the ten Tusscher et al. ventricular cell model. Previously validated K(+) channel formulations for SQT variants 1 and 3 were incorporated. Functional effects of the SQTS mutations on [Ca(2+)] i transients, sarcomere length shortening and contractile force at the single cell level were evaluated with and without the consideration of stretch-activated channel current (I sac). Without I sac, at a stimulation frequency of 1Hz, the SQTS mutations produced dramatic reductions in the amplitude of [Ca(2+)] i transients, sarcomere length shortening and contractile force. When I sac was incorporated, there was a considerable attenuation of the effects of SQTS-associated action potential shortening on Ca(2+) transients, sarcomere shortening and contractile force. Single cell models were then incorporated into 3D human ventricular tissue models. The timing of maximum deformation was delayed in the SQTS setting compared to control.

CONCLUSION

The incorporation of I sac appears to be an important consideration in modeling functional effects of SQT 1 and 3 mutations on cardiac electro-mechanical coupling. Whilst there is little evidence of profoundly impaired cardiac contractile function in SQTS patients, our 3D simulations correlate qualitatively with reported evidence for dissociation between ventricular repolarization and the end of mechanical systole.

Correlations between echocardiographic aortic elastic properties and left ventricular rotation and twist--insights from the three-dimensional speckle-tracking echocardiographic MAGYAR-Healthy Study

INTRODUCTION

There is an interaction between the left ventricle (LV) and the vascular system, which plays a crucial role in determining cardiac output. LV twist could be evaluated by three-dimensional speckle-tracking echocardiography (3DSTE) as the net difference of counterclockwise apical and clockwise basal LV rotations during systole. Aortic elasticity parameters could be measured during a routine transthoracic echocardiographic examination. The current study was designed to evaluate correlations between echocardiographic aortic elastic properties and LV rotational mechanics in healthy subjects.

METHODS

The present study comprised 26 healthy volunteers (mean age: 34.5 ± 9.8 years, 13 men). The following aortic elastic properties were measured from aortic data and forearm blood pressure values: aortic strain, distensibility and stiffness index (ASI). 3DSTE was used to measure basal and apical LV rotations and LV twist.

RESULTS

During 3DSTE, basal LV rotation proved to be -2.42 ± 1.43 degree, while apical LV rotation was 8.56 ± 1.43 degree, therefore LV twist was 11.01 ± 5.19 degree. Aortic strain (0.131 ± 0.094), distensibility (3.61 ± 2.54 cm² dynes(-1) 10(-6)) and ASI (4.08 ± 0.79) were also calculated. Apical LV rotation correlated with aortic distensibility (r = -0.36, P<0.05) and ASI (r = 0.41, P<0.05). LV twist showed similar correlation with ASI (r = 0.42, P<0.05).

DISCUSSION

Correlations exist between echocardiographic aortic elastic properties and 3DSTE-derived LV rotation and twist in healthy subjects.