Quantitation of left-ventricular asynergy by cardiac ultrasound

The clinical evaluation of regional delays in myocardial motion (myocardial asynchrony) has proved problematic, yet it remains an important functional parameter to evaluate. Prior attempts to quantify regional asynergy have m et with limited success, often thwarted by the low temporal resolution of i maging-system data acquisition. If a delay in onset of motion of 30-40 msec is clinically important ta measure, then data acquisition at frame rates o f 50-100 per second is required. This is avt of the current temporal resolu tion of angiographic, nuclear, or magnetic resonance studies. Only cardiac ultrasound can currently achieve the necessary frame rates. Furthermore, qu antitative studies into the accuracy with which a trained observer can iden tify computed regional myocardial asynchrony in a left-ventricular 2-dimens ional (2-D) image have shown that regional delays of <80 msec are not norma lly recognized in a moving image. This may be improved to 60 msec when eith er training is undertaken or comparative image review is used. However, thi s is still out of the temporal resolution required in clinical practice. Th us, visual interpretation of asynchrony is not sufficiently accurate. Two u ltrasound data sets based on either integrated backscatter or Doppler myoca rdial imaging data may provide the solution. Doppler myocardial imaging is a new ultrasound technique which, in either its pulsed or color Doppler for mat, can achieve the required temporal resolution (with temporal resolution s of 8 msec and 16 msec, respectively). In contrast, color Doppler myocardi al imaging, in its curved M-mode format can display the timing of events du ring the cardiac cycle for all in-plane myocardial segments. This should al low the quantitation of regional delay for all systolic and diastolic event s. Potentially, asynchrony due to regional ischemia, bundle branch block, v entricular premature beats, and ventricular preexcitation could all be iden tified and the degree of delay quantified. This overview will aim to establ ish the potential role of these new ultrasound methodologies in the recogni tion and quantitation of left-ventricular asynergy and how they might best be introduced into clinical practice. (C) 2000 by Excerpta Medico, Inc.