Usefulness of intravenous propranolol in predicting left anterior descending blood flow during anterior myocardial infarction

Angiographic assessment of prospectively determined non-invasive reperfusion indices in acute myocardial infarction

OBJECTIVE

To investigate the value of non-invasive reperfusion indices in acute myocardial infarction, avoiding the possible need for acute coronary angiography and subsequent angioplasty.

DESIGN

In a prospective angiographic study, seven potential ECG or clinical markers of reperfusion were analysed in 230 patients with acute myocardial infarction. In all patients two 12 lead ECGs were used: the ECG on admission and the ECG immediately before coronary angiography. Non-invasive markers of reperfusion determined just before coronary angiography were prospectively correlated to thrombolysis in myocardial infarction (TIMI) flow. Data analysis correlated these non-invasive indices with coronary flow (analysis A: TIMI 2-3 v TIMI 0-1 flow; analysis B: TIMI 3 v TIMI 0-2 flow).

RESULTS

A sudden decrease in chest pain was the most common sign of reperfusion (36%), followed by reduction in ST segment elevation by >/= 50% (30%), and the development of a terminal negative T wave (20%) in the lead with the highest ST segment elevation. Reduction in ST segment elevation by > or = 50% and the appearance of an accelerated idioventricular rhythm (AIVR) had the highest positive predictive value for reperfusion. For analyses A and B, the positive predictive values were 85% and 66% for resolution of ST segment elevation, and 94% and 59% for AIVR, respectively. The presence of three or more non-invasive markers of reperfusion predicted TIMI 3 flow accurately in 80% of cases.

CONCLUSIONS

The prospective use of non-invasive indices of reperfusion is simple, practical, and can be of value in assessing coronary patency in patients admitted with acute myocardial infarction. Using these indices, discrimination between TIMI 0-1 and TIMI 2-3 flow can be made with good accuracy. However, TIMI 3 flow cannot be determined reliably. The use of such non-invasive indices depends on the goal of reperfusion.

Failure of intravenous metoprolol to limit acute myocardial infarct size in a nonreperfused porcine model

The usefulness of intravenous beta-adrenergic receptor blockade in limiting infarct size when neither reperfusion nor collateral flow occurs is unknown. The effect of intravenous metoprolol on limiting myocardial infarct size was therefore examined in a nonreperfused porcine model. Closed-chest techniques were used to occlude the left anterior descending coronary artery, after which animals were randomized at 20 minutes to receive intravenous metoprolol, 0.75 mg/kg, or placebo. Infarct size examined at 5 hours with Evans blue and triphenyltetrazolium staining techniques was expressed as a percentage of total ventricular myocardium at ischemic risk. This percentage was not significantly different between the groups (84% +/- 5% with metoprolol vs 90% +/- 4% with placebo; p = 0.4). Myocardial infarct size was not significantly decreased at 5 hours by early administration of intravenous metoprolol when the infarct artery remained occluded and collateral flow was minimal.

Myocardial salvage after regional beta-adrenergic blockade

The aim of the study was to determine whether regional beta-adrenergic blockade via the coronary sinus limited myocardial damage after coronary artery occlusion in the canine model. Accordingly, open-chest anesthetized dogs were randomly allocated to one of three groups: a control group and groups treated with propranolol (in doses of 0.02, 0.2, and 2.0 mg/kg) given either intravenously or via the coronary sinus. The hypoperfused zone (i.e., risk area) and the extent of myocardial damage were assessed by autoradiography and triphenyltetrazolium chloride staining, respectively. Myocardial damage expressed as a percent of the hypoperfused zone was 84 +/- 5% in the control group (n = 9) and 78 +/- 7% (0.02 mg/kg, n = 7, NS), 63 +/- 6% (0.2 mg/kg, n = 7, p less than 0.05), and 62 +/- 7% (2.0 mg/kg, n = 9, p less than 0.02) in the groups receiving intravenous propranolol and 73 +/- 6% (0.02 mg/kg, n = 7, NS), 58 +/- 7% (0.2 mg/kg, n = 7, p less than 0.01), and 44 +/- 9% (2.0 mg/kg, n = 9, p less than 0.001) in groups receiving propranolol via the cardiac veins. There was a significant enhancement of myocardial salvage with increasing doses of propranolol delivered via the cardiac veins (linear regression trend, p less than 0.05). In contrast, myocardial damage expressed as a percent of the hypoperfused zone remained comparable with propranolol doses of 0.2 and 2.0 mg/kg administered intravenously (linear regression trend, NS).

IN CONCLUSION

(1) regional beta-adrenergic blockade via the cardiac veins afforded significant myocardial salvage and (2) the regional administration of propranolol resulted in significant reduction of myocardial damage in a dose-dependent fashion.

Protection of the ischemic myocardium during percutaneous transluminal coronary angioplasty

Therapeutic balloon coronary angioplasty provides a useful model for studying the effects of epicardial coronary artery occlusion in conscious humans. In addition, it is a potent model in which the effectiveness of interventions designed to ameliorate ischemia can be evaluated. Whereas intravenous beta-adrenergic blocking drugs and nitrates appear to have a limited protective effect, the regional (i.e., intracoronary) use of beta-adrenergic blocking drugs and calcium antagonists seem more potent. Currently, coronary venous retroperfusion with arterial blood does not appear practical, and the intraaortic balloon is a useful adjunctive measure in relatively few patients undergoing percutaneous transluminal coronary angioplasty. In contrast, the direct anterograde delivery of oxygen-rich blood or fluorocarbons holds promise as a reliable means of providing local myocardial protection. If ischemia could be markedly reduced, percutaneous transluminal coronary angioplasty might be applied safely in more high-risk clinical settings. In addition, if prolonged balloon inflation could be performed, there might be an increase in primary success rate and possibly a reduction in restenosis rate.

Effect of metaraminol during acute inferior wall myocardial infarction accompanied by hypotension: preliminary study

This study was designed to evaluate the effects of metaraminol (Aramine) in six patients with evolving acute inferior wall myocardial infarction accompanied by hypotension and warm limbs. There were 16 episodes of acute inferior wall ischemia, and the response to therapy was judged by evaluating blood pressure and ST segment and T wave abnormalities. Three patients received intravenous isosorbide dinitrate and two received streptokinase as the initial therapy. The mean ST segment elevation was significantly reduced (from 4.94 +/- 1 to 0.5 +/- 0.7 [p less than 0.0001]) after metaraminol infusion was initiated. The average T wave height also decreased (from 6.8 +/- 2 to -1.3 +/- 2.5 mm [p less than 0.0005]). The average heart rate decreased from 82 +/- 11 to 69 +/- 9 beats/min (p less than 0.05) and the mean arterial blood pressure increased from 81 +/- 12 mm Hg before metaraminol treatment to 126 +/- 8 mm Hg after treatment. All these changes occurred within a few minutes after metaraminol therapy was instituted. In 12 episodes, accelerated idioventricular rhythm appeared concomitantly with the resolution of ST segment elevation. Coronary angiography performed between 4 and 10 days after admission demonstrated significant obstruction in all infarct-related arteries, but none was totally occluded. Left ventricular function was normal in three patients and slightly hypokinetic in the inferior wall in two. These results indicate that in a selected group of patients with acute inferior myocardial infarction, metaraminol administration (in certain hemodynamic circumstances) can alleviate acute ischemia within a few minutes and thereby reduce ischemic injury.

Relationship between changes in ST segment elevation and patency of the infarct-related coronary artery in acute myocardial infarction

Forty-one patients with acute myocardial infarction and ST segment elevation were studied to determine the relationship between early changes in ST segment elevation, time to peak serum creatine kinase (CK), peak serum CK, left ventricular function, and patency of the infarct-related artery. ST segment elevation decreased by more than 40% within 8 hours of peak sigma ST in all patients with inferior infarction and in 10 of the 13 patients with anterior infarction and subtotal occlusion, but in none of the patients with anterior infarction and total occlusion (p = 0.003). The time to peak serum CK was related to the rate of decrease of ST segment elevation in patients with anterior (r = 0.59) and inferior (r = 0.71) infarction. In patients with anterior infarction, peak serum CK tended to be lower and left ventricular ejection fraction (EF) higher in those with rapid resolution of ST segment elevation than in those with persistent ST elevation (1721 +/- 1422 U/L vs 3285 +/- 1148 U/L, p less than 0.10, for peak CK; and 50.3 +/- 18.5% vs 41.2 +/- 12.8%, p = NS, for EF), but there was no difference in the patients with inferior infarction. Early resolution of ST segment elevation is an index of early spontaneous antegrade or collateral reperfusion in patients with acute myocardial infarction.

Relation of myocardial salvage to size of myocardium at risk in dogs

Infarct size varies in untreated animals subjected to coronary artery occlusion at the same anatomic site. The relation between the hypoperfused zone and the magnitude of myocardial salvage when different pharmacologic interventions are used remains to be established. Thus, in 95 anesthetized dogs, 1 minute after left anterior descending coronary occlusion, technetium-99m-labeled albumin microspheres (8 mCi) were injected into left atrium for the assessment of the hypoperfused zone. Fifteen minutes after coronary occlusion 42 dogs were randomized into a control group and 53 into a treated group. In the treated group, 6 dogs received nifedipine, 0.35 micrograms/kg followed by 2.4 micrograms/kg/hour; 7 received diltiazem, 0.2 mg/kg followed by 0.9 mg/kg/hour; 13 received bepridil, 2.5 mg/kg; 9 received cytochrome C, 2.5 mg/kg; 8 received rutosides, 200 mg/kg; and 10 received nifedipine plus cytochrome C. All drugs were administered intravenously. At 6 hours the dogs were killed and their hearts were cut into 3-mm-thick slices. Infarct size was determined by triphenyltetrazolium chloride staining; the hypoperfused zone was delineated by autoradiography. The dogs were retrospectively subgrouped as follows: those with small hypoperfused zones, i.e., less than 15% of the left ventricle (controls n = 8, treated n = 7) and those with large hypoperfused zones, i.e., more than 15% of the left ventricle (controls n = 34, treated n = 46). In dogs with large hypoperfused zones, treatment salvaged 42 +/- 3% of the myocardium destined to undergo necrosis, whereas in those with small hypoperfused zones 78 +/- 10% of myocardium was salvaged (p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Prevalence and significance of residual flow to the infarct zone during the acute phase of myocardial infarction

Residual flow to the infarct zone was assessed by coronary angiography during the acute phase of myocardial infarction in 130 patients. In 36 patients, the infarct-related coronary artery was not completely obstructed, thereby providing residual anterograde flow to the infarct area (Group I). Complete obstruction of the infarct vessel with residual flow to the infarct zone by means of collateral circulation was observed in 56 patients (Group II). Complete obstruction of the infarct vessel without residual flow was seen in 38 patients (Group III). Ejection fraction during the acute phase of infarction was found to be significantly higher in Group I (55 +/- 13%) than in either Group II (48 +/- 13%) or Group III (50 +/- 10%) (p less than 0.05). Group II patients had a longer history of angina pectoris (14.2 +/- 21.4 months) than did Group III patients (0.7 +/- 3.1 months) (p less than 0.01). Patients in Group I and Group II were more likely to be taking antianginal medication (56 and 54%, respectively) than were the patients in Group III (16%) (p less than 0.01). Thirty-seven patients in whom reperfusion techniques were not employed had repeat angiography in the chronic phase of infarction, enabling assessment of spontaneous changes in left ventricular function and coronary morphology.(ABSTRACT TRUNCATED AT 250 WORDS)