Myocardial thinning theories upended

By Eleanor McDermid, Senior medwireNews Reporter

Regional myocardial wall thinning is not necessarily indicative of transmural myocardial infarction, a study suggests.

The researchers found that thinned myocardium often has only limited scarring and, moreover, can recover function after patients undergo revascularization.

"We believe the data indicate that myocardial thinning is potentially reversible and therefore should not be considered a permanent state," say study author Raymond Kim (Duke University Medical Center, Durham, North Carolina, USA) and team in JAMA.

In 201 patients with regional thinning (end-diastolic wall thickness =5.5 mm), the thinned myocardium, detected on cardiovascular magnetic resonance (CMR) imaging, amounted to an average of 34% of the total left ventricular area. Scarring occupied 72% of the thinned area, on average; however, 18% of patients had limited scarring, involving no more than 50% of the thinned region.

Among 42 patients who underwent revascularization and had follow-up cine-CMR data, the extent of scarring within the thinned area significantly and inversely correlated with the change in wall thickening in the thinned area after treatment. It also negatively correlated with improvements in left ventricular ejection fraction.

Significant improvements were only seen in patients with limited scarring, who had an average 2.3 mm increase in absolute systolic wall thickening after revascularization. In these patients, average end-diastolic wall thickness increased from 4.4 mm before treatment to 7.5 mm after, no longer meeting the threshold for myocardial thinning.

Patients with limited scarring had an average of 95% stenosis in the artery supplying the thinned area. "Although speculative, this suggests that thinning of viable regions requires a significant reduction in resting blood flow and represents an extreme form of hibernating myocardium with a delicate balance between resting ischemia and infarction," say Kim et al.

The team found that clinical characteristics did not predict which patients would have limited scarring. Collateral flow to the thinned area was significantly poorer in patients with extensive than limited scarring, yet 41% of those with limited scarring lacked any visible collaterals.

Kim et al say their findings highlight the incomplete understanding of hibernating myocardium, and may help to explain why the Surgical Treatment for IsCHemic heart failure in Ischemic Cardiomyopathy (STICH) trial failed to find an association between baseline myocardial viability and survival after revascularization.

In an accompanying editorial, Marc Pfeffer and co-authors, from Brigham and Women's Hospital in Boston, Massachusetts, USA, also mention the STICH findings, saying that "the clinician is still left trying to decide what to do with a finding of viable myocardium."

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