Chronic Ischemic Dysfunction Research Articles

Flow-function relationships in chronic left-ventricular ischemic dysfunction: Impact of the transmurality of infarction

We examined flow-function relationships in humans with chronic coronary artery disease (CAD) in relation to the transmural extent of necrosis, aiming to distinguish the various pathophysiologic conditions that cause chronic ischemic dysfunction, ie, chronic hibernation (perfusion-contraction match) from chronic stunning (perfusion-contraction mismatch). Twenty-two patients (18 men, 61 +/- 13 years) with CAD and chronic contractile dysfunction (ejection fraction, 26% +/- 13%) and 6 volunteers underwent tagged and gadolinium (Gd)-DTPA contrast-enhanced magnetic resonance imaging as well as (13)NH(3)-positron emission tomography. The relationship between regional circumferential shortening strain (ECC), transmural necrosis, and absolute transmural myocardial perfusion (MBF) was examined quantitatively in dysfunctional segments (<10% ECC). Noninfarcted (<25% transmurality), dysfunctional myocardium presented a perfusion-contraction mismatch, as indicated by a 72% reduction (to -5% +/- 4% shortening) of ECC, versus only a 12% (to 63 +/- 20 mL/min/100 g) reduction of transmural MBF. With increasing amounts of necrosis, reductions between perfusion versus contraction became increasingly matched, ie, dysfunctional segments with a greater than 75% transmural extent of necrosis had a 57% reduction of MBF (to 30 +/- 17 mL/min/100 g), for a similar severe reduction of 80% of ECC (to -3% +/- 3% shortening). Noninfarcted, dysfunctional human myocardium mostly presents with a perfusion-contraction mismatch, consistent with stunning. By contrast, dysfunctional myocardium presenting with a perfusion-contraction match is always associated with significant amounts of necrosis.

Attenuation-corrected 99mTc-MIBI SPECT in overweight patients with chronic ischaemic dysfunction: a comparison to NH3 PET and implications for the diagnosis of myocardial viability

We determined the value of attenuation correction (AC) of myocardial perfusion estimation with (99m)Tc-MIBI SPECT in overweight patients by comparison of uncorrected (filtered back-projection (FBP) and corrected (an iterative algorithm with a measured attenuation coefficients map (FL-AC)) (99m)Tc-MIBI relative uptake to perfusion data obtained in the same patients with NH3 PET. In addition, the impact of attenuation correction for the assessment of myocardial viability with (99m)Tc-MIBI SPECT was determined using FDG PET as the reference method. Thirty consecutive overweight patients (BMI=28+/-4) with left ventricular dysfunction underwent a resting (99m)Tc-MIBI SPECT and a PET study (NH3 and FDG). (99m)Tc-MIBI SPECT scans were reconstructed without attenuation correction (FBP) and with attenuation correction (FL-AC). The left ventricle was divided into 16 segments, in which the relative uptake was quantified using circumferential profiles. A relative uptake > or = 60% was considered consistent with viable myocardium for FDG and MIBI. The absolute difference between (99m)Tc-MIBI SPECT and NH3 PET uptakes was less pronounced in the inferior (12+/-10% vs. 17+/-12%, P<0.001), anteroseptal (12+/-11% vs. 16+/-12%, P=0.009) and septal (15+/-12% vs. 18+/-14%, P=0.003) regions (FL-AC vs. FBP, respectively). The sensitivity of MIBI for diagnosing myocardial viability increased from 83 to 100% (P=0.034), without loss in specificity. Attenuation correction improves myocardial perfusion estimation by (99m)Tc-MIBI SPECT in the inferior, anteroseptal and septal regions and increases its sensitivity for the diagnosis of myocardial viability.

Invited commentary

The incidence of severe left ventricular dysfunction secondary to chronic coronary artery disease is increasing. In coronary artery disease, flow reserve decreases in proportion to the degree of stenosis and it may lead to intermittent or chronic episodes of ischemia and, consequently, postischemic stunning. If these episodes are frequent with incomplete recovery of contractile function before the next insult, this may trigger the development of myocardial hibernation and might play a role in the development of chronic reversible left ventricular dysfunction. In the presence of viable myocardium, coronary revascularization would reduce the chronic ischemic dysfunction by restoring flow reserve and improve left ventricular function, heart failure symptoms, and prognosis. However, surgery in these patients is associated with higher morbidity and mortality. Assessment of myocardial viability, and thus a careful selection of patients who may benefit from revascularization, is necessary to offset this higher risk.

Morphological bases for thallium-201 uptake in cardiac imaging and correlates with myocardial blood flow distribution.

To determine the morphological bases of thallium-201 myocardial distribution in chronic cardiac dysfunction and their relation to myocardial blood flow, myocardial slices from ten excised hearts of five chronic ischaemic heart disease patients and five idiopathic dilated cardiomyopathy patients, were imaged on a gamma camera to quantitate the uptake of thallium-201, injected 4 h before surgery, and myocardial blood flow from distribution of technetium-99m-labelled human albumin microspheres injected during surgery. Tracer distribution was correlated with histologically assessed myocardial fibrosis and myocytolysis. Thallium-201 uptake was inversely related to fibrosis (r = -0.73, in ischaemic heart disease, r = -0.65 in idiopathic dilated cardiomyopathy). In ischaemic heart disease, myocardial blood flow was related neither to thallium-201 uptake (r = 0.41) nor to the extent of fibrosis (r = -0.48). In this group, segments with normal or mildly reduced thallium-201 uptake showed significantly lower fibrosis than those with moderate or severe uptake defects (5 +/- 7% and 7 +/- 11% vs 33 +/- 14% and 42 +/- 12%, respectively, P < 0.0001. In a clinical model of chronic ischaemic dysfunction, despite severely depressed myocardial blood flow, extensive areas of myocardium devoid of significant structural impairment are present. Thallium-201 uptake effectively discriminates regions with preserved viability from those with relevant myocardial damage.

722-3 Low Dose Dobutamine Predicts Recovery of Global but not Regional Left Ventricular Function After Revascularlzatlon In Patients with Chronic Ischemic Dysfunction

The purpose of this study was to evaluate the ability of low dose (LD) dobutamine stress echocardiography (DSE) to independently predict recovery of global and regional left ventricular (LV) function following coronary artery bypass surgery (CABG) in patients with ischemic LV dysfunction. Sixteen patients with multivessel coronary artery disease and reduced ejection fraction (EF = 0.25 ± 0.08) underwent DSE prior to CABG, and 2D echo at 20 ± 17 weeks post-CABG (FlU). Global EF was measured at baseline, LD and at F/U; improvement was defined as an increase in EF of &gt; 0.05. Global EF at F/U improved in 11/16 pts (69%). All 11 (100%) pts had improvement in EF on LD DSE. Improvement in regional function was assessed in segments (segs) that were akinetic (AK) or severely hypokinetic (SHK) at baseline. Of 147 SHK/AK segs at baseline, 27 (18%) had LD augmentation; of these 27 segs, 13 (48%) improved on FlU. Of 120 SHK/AK which did not augment at LD, 34 (28%) improved at F/U. The sensitivity (SENSI). specificity (SPECI), positive (PPV) and negative predictive values (NPV) of LD augmentation for predicting improvement in regional and global LV function were: SENSI SPECI PPV NPV p Regional 38% 86% 48% 72% * 0.05 * Global 100% 60% 85% ‡ 100% 0.02 ‡ 1) Improvement in EF during LD DSE predicts recovery of global LV function with a PPV of 85%, and 2) Failure of individual AK or SHK segments to improve with LD DSE predicts lack of recovery at F/U with a NPV of 72%. Low dose dobutamine stress echocardiography can therefore be used to predict recovery of global function and lack of recovery of regional ventricularfunction following revascularization in patients with chronic ischemic dysfunction. It may be of relative greater value in predicting global as compa red to regional function.