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ICVTS Invited on-line discussion A

Mount Sinai Medical Center, 1190 Fifth Avenue, New York, NY 10029, USA

Stress Doppler echocardiography of the internal thoracic artery – a new non-invasive approach for functional assessment after minimally invasive coronary bypass grafting

eComment: Marx and colleagues [1] describe a novel approach for functional assessment of the left internal thoracic artery (LITA) to left anterior descending artery bypass graft. Their technique, which is based on transcutaneous Doppler assessment of the LITA waveform is unique because it allows for post-operative non-invasive assessment of the LITA graft after the chest is closed. This lends itself to use in the post-operative phase when there are clinical questions of graft function. Although angiography remains the gold-standard for graft assessment, it provides anatomical, but not functional, study of the graft. The technique of Marx et al. provides a means of functional graft assessment as, unlike angiography, a phasic pattern to graft flow can be demonstrated – this ability to demonstrate changes in systolic and diastolic flow pattern is the major strength of the Doppler approach.

The authors have described the use of Doppler to assess LITA flow after coronary artery bypass graft (CABG) to the LAD via left thoracotomy (MIDCAB approach). The MIDCAB technique as described by the authors included LITA harvest to the second rib only. Presumably, it was the residual proximal LITA, which remained attached to the chest wall, that was studied by Doppler examination. It is unclear whether harvest to the second rib is a choice used for only their MIDCAB procedures, or whether they also stop at the second space for sternotomy cases. If the limited harvest is only a feature of the MIDCAB approach, but not of their technique for conventional CABG via sternotomy, then one would be concerned of a possible compromise in surgical principle to fulfill the minimally invasive approach or desire to facilitate Doppler assessment. It is not stated whether the technique can be as readily applied in sternotomy cases, where the LITA has been entirely detached from the chest wall. Because the MIDCAB operation is currently rarely performed, adaptation of their technique to sternotomy CABG cases will be required for Doppler LITA assessment to have wide clinical applicability.

The technique described by Marx and coworkers is however as yet unvalidated. While the authors have clearly demonstrated increase in diastolic LITA flow compared to the ungrafted right ITA, and also increase in diastolic flow on exercise, the data do not allow correlation of the stress Doppler pattern with anastomotic patency, graft quality or clinical outcome. The authors have demonstrated what the ‘normal’ flow patterns are for presumed adequate LITA-LAD grafts, but it is not known if those grafts were truly adequate (as systematic graft study was not undertaken). No abnormal flow patterns were observed; ability to recognize and interpret abnormal flow patterns is however crucial to clinical applicability of this technique. Future studies are required to correlate the Doppler findings with existing measures of graft function (such as clinical signs, electrocardiography and angiography). It would be useful to define Doppler patterns that are indicative of graft problems such as kinking, anastomotic stenosis or occlusion, and problems with distal run-off. Animal studies may be helpful in this regard. Future clinical study should combine systematic angiography with routine stress Doppler. The Doppler remains a useful research tool for evaluating post-operative graft function but requires further investigative study before it can be adopted into clinical practice.

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1. Marx R, Kalweit G, Sunderdiek U, Jax TW, Klein RM, Szabo S, Hoffmeister HM, Guelker H. Stress Doppler echocardiography of the internal thoracic artery – a new non-invasive approach for functional assessment after minimally invasive coronary bypass grafting. Interact CardioVasc Thorac Surg doi:doi:10.1510/icvts.2006.129007.

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