Impact of right ventricular volume overload on left ventricular strain and torsion in patients after surgical repair of tetralogy of Fallot: analysis by novel 3-dimensional speckle tracking echocardiography

Professor Cheung, Yiu Fai   (Principal Investigator)

30

2009-12-01

60000

Impact of right ventricular volume overload on left ventricular strain and torsion in patients after surgical repair of tetralogy of Fallot: analysis by novel 3-dimensional speckle tracking echocardiography

echocardiography, tetralogy of Fallot, ventricular function

Cardiovascular Research

200907176049

Small Project Funding

2009

Completed

Right ventricular dilation occurs commonly after surgical repair of tetralogy of Fallot (TOF) as a result of chronic pulmonary regurgitation. Importantly, significant right ventricular dilation in association with severe chronic pulmonary regurgitation has been shown to be associated with systolic and diastolic dysfunction, ventricular arrhythmias, and impairment of exercise capacity. Although right ventricular dilation and dysfunction have been shown to contribute significantly to long-term morbidity and mortality, left ventricular dysfunction has been found to be independently associated with adverse outcomes in the long-term. While the cause of left ventricular dysfunction is unclear, abnormal ventricular-ventricular interaction has been speculated to be a potential mechanism. Systolic deformation, as quantified by strain, and twisting motion of the left ventricle has been shown to be strong indicators of ventricular performance. In TOF patients, the potential importance of altered left ventricular systolic deformation is suggested by previous finding of delayed systolic myocardial deformation of the septum compared with the lateral wall. Nonetheless, previous assessment of myocardial deformation in these patients was limited to one-dimensional analysis by tissue Doppler imaging, namely the longitudinal dimension, while deformation in the circumferential and radial dimensions was not determined. Indeed, the more sensitive nature of circumferential deformation has been shown recently in adults with myocardial ischaemia. Apart from systolic strain, twisting motion of the left ventricle, so-called torsion, is also known to play an important role with respect to left ventricular ejection and filling and shown to be sensitive to changes to regional and global left ventricular function. Torsional deformation of left ventricle is characterized by systolic twisting and diastolic untwisting along its long axis as a result of the opposite rotation of the cardiac apex and base. Tagged magnetic resonance imaging studies have revealed left ventricular torsion to be a relatively load-independent index of contractility. However, the clinical application of magnetic resonance imaging in the assessment of ventricular torsion has been limited by cost and complexity. The newly introduced three-dimensional speckle tracking echocardiography (STE) enables simultaneous imaging of all segments of the left ventricle and tracking of motion vectors of the speckles in three dimensions from the volume dataset, hence providing complete angle-independent analysis of left ventricular myocardial deformation beyond the two-dimensional scan plane. Additionally, as segments of the left ventricular apex and base are imaged simultaneously, left ventricular torsion can be accurately assessed from one single acquisition. Another advantage of this technique is simultaneous calculation of three-dimensional volumes and ejection fraction. This technique has recently been validated against sonomicrometry in animal models. While ventricular-ventricular interaction has been proposed as a cause of left ventricular dysfunction in patients after surgical repair of TOF, the exact mechanism remains unclear. Advances in three-dimensional echocardiography provide an opportunity to interrogate potentially abnormal ventricular-ventricular interaction from the new perspective of cardiac mechanics. Our recent findings in these patients of relationships between left ventricular mechanical dyssynchrony and severity of pulmonary regurgitation and right ventricular dilation suggest that abnormal myocardial deformation may play a pivotal role mediating abnormal ventricular-ventricular interaction. We therefore hypothesize that right ventricular volume overload is associated with abnormal left ventricular deformation and twisting in patients after surgical repair of TOF. The proposed study is, to our knowledge, the first to quantify left ventricular three-dimensional strain and torsion in patients after TOF repair and to determine the impact of right ventricular volume overload on these indices of deformation. The primary objective of the study is to test the hypothesis that right ventricular volume overload is associated with abnormal left ventricular deformation and twisting in patients after surgical repair of TOF. The issues to be addressed include the followings: i) the effect of right ventricular dilation on left ventricular three-dimensional systolic strain, ii) the effect of right ventricular dilation on left ventricular torsion, iii) the functional implications of abnormal three-dimensional strain and left ventricular torsion in terms of their effects on left ventricular global function and exercise capacity, and iv) the impact of pulmonary valve replacement with reduction of right ventricular volume overload on left ventricular deformation and torsion