Infarct size--can it be measured or modified in humans?

Reperfused rat myocardium subjected to various durations of ischemia: estimation of the distribution volume of contrast material with echo-planar MR imaging

PURPOSE

To estimate and compare the fractional distribution volume (fDV) of gadodiamide injection and technetium 99m-diethylenetriaminepentaacetic acid (DTPA) in the reperfused myocardium of rat hearts subjected to various durations of ischemia.

MATERIALS AND METHODS

Magnetic resonance (MR) imaging and autoradiography were performed in rats subjected to 20, 30, 40, or 60 minutes of regional ischemia followed by 1 hour of reperfusion. The fDVs of gadodiamide injection and (99m)Tc-DTPA were measured and compared by using inversion-recovery echo-planar imaging and autoradiographic phosphor imaging, respectively.

RESULTS

The mean fDV of both tracers (gadodiamide and (99m)Tc-DTPA) in normal myocardium was 18% +/- 1, whereas that in the entire area at risk increased significantly (P <.05) with 20, 30, 40, and 60 minutes of ischemia to 32% +/- 1, 57% +/- 4, 66% +/- 2, and 68% +/- 2, respectively. The fDV was significantly (P <.05) greater in the core of infarction-78% +/- 4, 89% +/- 5, and 88% +/- 5 with 30, 40, and 60 minutes of ischemia, respectively-than in the normal myocardium or in the area at risk.

CONCLUSION

The fDV of MR contrast material in the periinfarcted rim was significantly (P <. 05) greater than that in the normal myocardium, but significantly less than that in the core of infarcted myocardium.

Is routine echocardiography useful in patients hospitalized for chest pain? Evidence of areal myocardial dysfunction detected only by echocardiography

To assess the diagnostic value of routine two-dimensional echocardiography in the coronary care unit setting, we studied 81 unselected patients admitted for acute chest pain. Using electrocardiography (ECG), clinical history and serum markers of myocardial injury, the patients were retrospectively diagnosed as having had definite acute myocardial infarction (AMI) with (n=13) or without (n=31) previous infarction, possible AMI with (n=14) or without (n=15) previous infarction, and non-coronary cardiac or other causes of chest pain (n=8). Abnormal wall motion was observed in 75/77 patients with a cardiac origin of symptoms (sensitivity 97%), and there were no false-positive wall motion findings. In the 73 patients who were finally diagnosed with coronary artery disease (CAD), echocardiography showed wall motion abnormality in at least one additional coronary territory area in which there were no diagnostic ECG changes for 56% of patients with CAD (41/73) (P<0. 001). These areas were considered to be indicative of the presence of myocardium at risk for future cardiac events. We conclude that in addition to being a sensitive and accurate tool for detection of ischaemic wall motion abnormalities, two-dimensional echocardiography can give valuable information about the area of myocardium at risk. Therefore, therapeutic decisions can be affected by the findings of the routine echocardiographic examination, which is recommended even in unselected coronary care unit patients.

Relation between ischemia time, infarct size, and left ventricular function in humans

BACKGROUND

Experimental studies indicate that duration of ischemia is a major determinant of myocardial infarct size, but only limited information is available about the relation between ischemia time and infarct size in individual patients. This prospective study sought to document the role of ischemia time as a determinant of infarct size in humans.

METHODS AND RESULTS

We studied 61 patients (50 men, 11 women) 57 +/- 11 years old admitted with a first infarct (31 anterior, 30 inferior) who underwent continuous 12-lead ECG monitoring to document ischemia time. Infarct size (32-point QRS score on day 7) and changes in regional myocardial wall motion (echocardiography) during the following month were related to ischemia time. Among patients with < 3 hours of ischemia (n = 16), mean infarct size on day 7 was 21 +/- 13% of potential infarct size; in patients with 3 to 6 hours of ischemia (n = 23), infarct size was 38 +/- 18% of potential (P < .05 versus 0 to 3 hours of ischemia); and in patients with 6 to 9 hours of ischemia (n = 10), infarct size was 66 +/- 14% of potential (P < .05 versus 3 to 6 hours). In contrast, the 12 patients with an ischemia time > 9 hours had a final infarct size of 77 +/- 10% of potential (P < .01 versus 3 to 6 hours). Multivariate regression identified size of risk region, duration of ischemia, and degree of initial ST-segment elevation as independent predictors of infarct size, of which the most important variable was ischemia time. The regression models accurately predicted both individual absolute infarct size (R2 = .83) and individual infarct/risk ratio (R2 = .74). Patients with < 6 hours of ischemia exhibited significant recovery of myocardial wall motion by day 7 (wall motion score, 2.1 +/- 1.4 versus 5.7 +/- 3.2 on day 1, P < .01). Patients with 6 to 9 hours of ischemia had some recovery by 1 month (score, 6.3 +/- 4.4 versus 10.9 +/- 3.8 on day 1, P < .01), but patients with > 9 hours of ischemia had little recovery of wall motion by 1 month (score, 10.3 +/- 4.5 versus 12.8 +/- 3.1 on day 1, P < .05).

CONCLUSIONS

Measurement of ischemia time allows improved prediction of infarct size in humans. Significant myocardial salvage and functional recovery may be achieved by reperfusion up to 9 hours after coronary occlusion. Continuous ST-segment monitoring should be used to measure ischemia time and guide interventions to reperfuse the infarct artery.

A method for enzyme- and immunohistochemical staining of large frozen specimens

A method for large specimen cryosectioning is described. Specimens of pig heart ventricles were lightly fixed by microwave irradiation, embedded in 10% gelatin, frozen in hexan chilled with dry ice, and sectioned using an LKB 2250 PMW cryomicrotome. The sections were collected on transparent film and transferred onto glass slides. Standard histological, enzyme- and immuno-histochemical staining techniques were used. The present method allowed cryosectioning with sections of good quality which could be used for enzyme- and immuno-staining. For studies of experimental myocardial infarction, staining for phosphorylase and Periodic Acid Schiff outlined the ischemic area and antibodies against plasma fibronectin and fibrinogen delineated the infarcted myocardium.

Calcium-channel blockers in acute myocardial infarction

The calcium-channel blockers are useful in treating a variety of cardiovascular disorders. Due to their antiischemic and spasmolytic properties, these agents have been studied in the prophylaxis and treatment of acute myocardial infarction. This article reviews this application with respect to reduction of mortality, infarct size, and reinfarction rate. Of the agents currently available for clinical use, nifedipine has been studied most extensively. This agent shows no beneficial effects in this setting and its use may in fact be harmful. Of the few trials that have been conducted with verapamil, none have shown decreased mortality. Verapamil may reduce infarct size although further confirmation is required. Diltiazem is the only agent that has been shown to have short- and long-term benefits in the patient with acute myocardial infarction. Proper patient selection is of utmost importance in ensuring successful therapy. In particular, those patients with non-Q-wave infarctions and/or normal left ventricular function can be expected to derive the most benefit in terms of reducing mortality and reinfarction rate associated with the acute event.