Assessment of drug intervention on the ischemic myocardium: serial imaging and measurement with computerized tomography

Controlled myocardial infarction induced by intracoronary injection of n-butyl cyanoacrylatein dogs: a feasibility study

Concentrated ethanol has been used to induce controlled myocardial infarct in patients with hypertrophic obstructive cardiomyopathy. We report the acute and early follow-up results of an alternative agent, n-butyl cyanoacrylate (n-BCA) glue, in a dog model. In 11 mongrel dogs, we injected n-BCA into different branches of the left anterior descending artery. Biplane left ventriculogram and coronary angiogram were performed before and after injection. In the surviving animals, we performed programmed stimulation (PS) to test for inducible ventricular tachycardia (VT) 48 days later. Following euthanasia, the removed hearts were studied with computer tomography (CT) and gross and histologic examination. Three dogs were lost before injection. Four dogs died within 2 hr to 4 days, and four animals survived 48 days. Accidental embolization of n-BCA into nontarget vessels was documented in four subjects. In the n-BCA-injected animals, homogeneous circumscribed scar was demonstrated by CT and histology. The glue was confined strictly to the tributary of the injected vessel, infiltrating arterioles of 14 mum. There was intense granulomatous reaction (GR) in the vessel wall and in the surrounding myocardium. Remote areas were unaffected. Monomorphic VT was not inducible with PS. We report a feasibility study of n-BCA injection to selected coronary arteries of dogs to cause controlled myocardial infarction. We demonstrated that the glue does not escape from the target artery through capillaries or small collateral vessels and thus produces a sharply demarcated and homogeneous scar, which is confined strictly to the supply zone of the injected vessel. Improvement of the delivery system is necessary to eliminate inadvertent embolization. Long-term follow-up is needed to study the GR induced by n-BCA.

Changes in regional myocardial cross-sectional area during brief coronary occlusion and reperfusion in conscious dogs

The effect of a brief period of coronary occlusion on a regional myocardial cross-sectional area was studied in 6 conscious dogs. Subendocardial segment length and wall thickness were continuously measured with a sonomicrometer in the central ischemic area perfused by the left circumflex coronary artery during a 2-min circumflex occlusion and subsequent reperfusion. Measurements were repeated before and after collateral development induced by 180 +/- 30 (SEM) 2-min circumflex occlusions (20 +/- 3 days). In order to evaluate the changes in regional myocardial volume, end-diastolic regional cross-sectional area was calculated as a product of end-diastolic segment length and wall thickness. Before collateral development, end-diastolic regional cross-sectional area transiently decreased 1.4 +/- 0.6% (NS) at 10 sec following sudden coronary occlusion, thereafter gradually increased to 3.7 +/- 1.0% (P less than 0.05) at the end of a 2-min occlusion. At 10 sec of reperfusion, end-diastolic regional cross-sectional area further increased to 7.0 +/- 1.1% (P less than 0.05) probably due to increased intravascular volume. Increase in end-diastolic regional cross-sectional area was still 2.5 +/- 0.6% (NS) at 3 min after the release of occlusion. After collateral development, the changes in end-diastolic regional cross-sectional area were 0.1 +/- 0.1% (NS), 0.4 +/- 0.3% (NS), 1.0 +/- 0.6% (NS) and 0.2 +/- 0.4% (NS), respectively. Thus, a significant increase in the regional myocardial cross-sectional area occurs during a brief period of coronary occlusion and reperfusion.

Effect of hyperosmotic mannitol on magnetic resonance relaxation parameters in reperfused canine myocardial infarction

To determine how administration of a hyperosmotic agent alters regional nuclear magnetic resonance (NMR) relaxation parameters and imaging characteristics in ischemic-reperfused myocardium, 7 dogs were infused with mannitol for 15 minutes before and after the release of a 3 hour left anterior descending coronary artery (LAD) occlusion. Nine control animals received normal saline during the 3 hour occlusion and 1 hour reperfusion periods. Normal posterior left ventricular (LV) wall and the ischemic anterior LV wall (risk area) myocardium was sampled for calculation of segmental microsphere myocardial blood flow, % tissue water content, NMR relaxation times (T1, T2) and myocyte ultrastructure using electron microscopy. Mean infarct T1 values were 14% greater than normal segments in saline-treated controls, but only 5% greater after mannitol. The difference in tissue water content between infarcted and normal segments was 4% in saline-treated (83 vs. 79%) compared to 2% in mannitol-treated dogs (79 vs. 77%). T1, T2 and % water content of control infarct segments were greater than treated infarcts (p less than 0.01). T1 and T2 rose as occlusion flow fell below 0.5 ml/min/g in control hearts but did not rise until flows were reduced to 0.1 ml/min/g in mannitol-treated hearts. Areas of increased signal in T1 and T2 NMR images correlated well with histochemical infarct volume (r = 0.98, SEE = 1.1 cc) in mannitol-treated dogs, but infarct borders were qualitatively less well-defined than in controls. We concluded that mannitol (1) diminishes tissue edema and reduces NMR relaxation parameters (T1, T2) in infarcted myocardium; and (2) attenuates the rise in T1 and T2 and ultrastructural myocyte injury in ischemic-reperfused myocardium.

The usefulness of x-ray computed tomography for the diagnosis of myocardial infarction

Conventional and enhanced computed tomographic (CT) examinations were performed in 103 patients with myocardial infarction for evaluation of the diagnostic usefulness of CT. After intravenous bolus injection of contrast material, an initial filling defect and late enhancement of the infarcted myocardium appeared on the cardiac CT images. These two findings were direct evidence of myocardial infarction; the former was found mostly in the patient with recent myocardial infarctions, and the latter was recognized both in those with recent and those with "remote" infarctions. Wall thinning at the site of infarction was found by enhanced CT mostly in patients with anteroseptal or extensive anterior infarctions, and was rarely found in patients with inferoposterior infarctions. Left ventricular aneurysms and ventricular thrombi were found by enhanced CT in 39 and 23 of the 103 subjects, respectively, and the sensitivity of CT in detecting intracardiac thrombi was higher than that of two-dimensional echocardiography. Calcification of the myocardium and pericardial effusion associated with myocardial infarction were also detected by conventional nonenhanced CT. Thus, cardiac CT was found to be a useful test in evaluating patients with myocardial infarction.