Incidence of stunned, hibernating and scarred myocardium in ischaemic cardiomyopathy

Different criteria to identify residual viability in chronically dysfunctioning myocardium in patients with coronary artery disease (CAD) can be derived by the combined assessment of myocardial blood flow (MBF) and glucose utilisation (MRG) using positron emission tomography (PET). The aim of this study was to evaluate, in a large number of patients, the prevalence of these different patterns by purely quantitative means.

One hundred and sixteen consecutive patients with ischaemic cardiomyopathy (LVEF ≤40%) underwent resting 2D echocardiography to assess regional contractile function (16-segment model). PET with ¹⁵O-labelled water (H₂¹⁵O) and ¹⁸F-fluorodeoxyglucose (FDG) was used to quantify MBF and MRG during hyperinsulinaemic euglycaemic clamp. Dysfunctional segments with normal MBF (≥0.6 ml min⁻¹ g⁻¹) were classified as stunned, and segments with reduced MBF (<0.6 ml min⁻¹ g⁻¹) as hibernating if MRG was ≥0.25 μmol min⁻¹ g⁻¹. Segments with reduced MBF and MRG <0.20 μmol min⁻¹ g⁻¹ were classified as transmural scars and segments with reduced MBF and MRG between 0.20 and 0.25 μmol min⁻¹ g⁻¹ as non-transmural scars.

Eight hundred and thirty-four (46%) segments were dysfunctional. Of these, 601 (72%) were chronically stunned, with 368 (61%) having normal MRG (0.47±0.20 μmol min⁻¹ g⁻¹) and 233 (39%) reduced MRG (0.16±0.05 μmol min⁻¹ g⁻¹). Seventy-four (9%) segments with reduced MBF had preserved MRG (0.40±0.18 μmol min⁻¹ g⁻¹) and were classified as hibernating myocardium. In addition, 15% of segments were classified as transmural and 4% as non-transmural scar. The mean MBF was highest in stunned myocardium (0.95±0.32 ml min⁻¹ g⁻¹), intermediate in hibernating myocardium and non-transmural scars (0.47±0.09 ml min⁻¹ g⁻¹ and 0.48±0.08 ml min⁻¹ g⁻¹, respectively), and lowest in transmural scars (0.40±0.14 ml min⁻¹ g⁻¹, P<0.01). MRG was comparable in hibernating and stunned myocardium with preserved MRG (0.40±0.19 μmol min⁻¹ g⁻¹ vs 0.46±0.20 μmol min⁻¹ g⁻¹, NS), and lowest in stunned myocardium with reduced MRG and transmural scars.

Chronic stunning is more prevalent than expected. The degree of MRG reduction in stunned myocardium may disclose segments at higher risk of permanent damage.