Role of Tissue Doppler and Strain Echocardiography in Current Clinical Practice

Abstract

The motion of a muscle, is performed only by the Carnous fibers, and each Carnous fiber has a power of contracting itself…. The force of the whole Muscle is but an aggregate of the contractions of each particular fiber. — —William Croone in De ratione motus musculorum (On the Reason of the Movement of the Muscles), 1664 Visual or semiautomated tracking of the endocardial border provide estimates of cardiac volume, which are used to derive ejection fraction, a quantitative indicator of ventricular function. However, the heart is a complex mechanical organ that undergoes cyclic changes in multiple dimensions that ultimately effect a change in chamber volume that results in ejection of blood. Regardless of imaging technique, ejection fraction is unable to provide information on the underlying myocardial mechanical activity. Also, ejection fraction reflects the sum contribution of several regions and does not provide information on regional function. Regional function assessed visually is subjective and prone to error.1 Quantification of regional myocardial activity (deformation) was feasible only in experimental studies by use of markers attached directly to the myocardium, a technique not practicable in the clinical realm.2 Myocardial tagging with cardiac magnetic resonance (CMR) introduced the opportunity to noninvasively track regional myocardial mechanics.3,4 Modifications to the filter settings on pulsed Doppler to image low-velocity, high-intensity myocardial signal rather than the high-velocity, low-intensity signal from blood flow allows similar assessment by ultrasound. This technique is commonly referred to as tissue Doppler imaging (TDI) or Doppler myocardial imaging.5 The TDI method depicts myocardial motion (measured as tissue velocity) at specific locations in the heart. Tissue velocity indicates the rate at which a particular point in the myocardium moves toward or away from the transducer. Integration of velocity over time yields displacement or the absolute distance moved by that point …