Scanning technique shows if heart has irreversible damage
Authors: S. Gottlieb
Journal: BMJ (2000)

A specialised technique using contrast enhanced magnetic resonance imaging can accurately predict which patients with heart disease will benefit the most from undergoing revascularisation, according to a new study.

In the study 50 people who were already scheduled to undergo bypass surgery or angioplasty first underwent contrast enhanced magnetic resonance imaging. The screen was highly accurate at predicting which hearts had irreversible myocardial damage and therefore would not benefit from revascularisation.

On the scan, regions of the heart that were dysfunctional but not  before revascularisation were more likely to experience improvement in the global mean wall-motion score and in the ejection fraction after revascularisation (New England Journal of Medicine 2000;343:1445-53).

One of the study's authors, Dr Robert Judd of the Feinberg Cardiovascular Research Institute at Northwestern University Medical School in Chicago, Illinois, said that if an area of the heart was hyperenhanced or bright, that area would not improve after surgery or angioplasty.

He added that bright sections had only a 2% chance of improving after such treatments. As angioplasty and bypass surgery are not free of risk, the magnetic resonance scan may help to identify people for whom the risks of treatment outweigh the benefits, he said.

In the study, contractility improved after revascularisation in 256 of 329 myocardial regions where there was no hyperenhancement, compared with only one of 58 regions with hyperenhancement of more than 75% of tissue.

For regions of the hearts with intermediate levels of hyperenhancement (1% to 75% of the tissue), the extent of improvement in systolic function after revascularisation decreased progressively as the transmural extent of the hyperenhancement increased.

The technique involves injecting patients with gadolinium, a contrast enhancing dye, and then performing magnetic resonance imaging. Unlike other imaging techniques, this type of imaging provides a view of the entire thickness of the heart wall, not just the outer portions, Dr Judd explained.

Doctors have long known that the identification of viable myocardium is useful in predicting which patients will have increased left ventricular ejection fractions and improved survival after revascularisation.

Currently, non-invasive methods for assessing myocardial viability—such as positron emission tomography and dobutamine echocardiography—have proved clinical utility, but each has limitations that reduce its diagnostic accuracy. They interpret myocardial viability, for example, as an all or  phenomenon within a myocardial region, as none of the methods can assess the transmural extent of viability of the ventricular wall.

The availability of an accurate, noninvasive method of distinguishing viable myocardium from myocardium that has been irreversibly injured as a result of hibernation is important for clinical decision making, wrote Dr George Beller of the University of Virginia Health System in Charlottesville in an accompanying editorial (pp 1488-90 in the same issue). Such a tool would enable physicians to identify the patients with coronary artery disease and left ventricular dysfunction at rest who would benefit most from revascularisation strategies, he wrote.