Risk assessment in patients with acute myocardial infarction treated with thrombolysis

University dissertation from Stockholm : Karolinska Institutet, Karolinska Institutet, Stockholm Söder Hospital

Abstract: Risk stratification in patients with acute myocardial infarction is essential for guiding the clinical decision concerning management. Thrombolytic therapy and other new management policies have led to a significant reduction in mortality from myocardial infarction. Several clinical variables and non-invasive methods have been shown in post-infarction studies to provide independent prognostic information. However, risk stratification of patients with myocardial infarction treated with thrombolysis is more complicated and somewhat controversial, especially if assessments are made prior to discharge. In the present study, the risk was investigated before hospital discharge in consecutive patients given thrombolytic therapy for myocardial infarction. The study comprised 101 patients (73 men and 28 women) aged 64±9 years (range 4575). The patients underwent clinical risk assessment, 99mTc sestamibi single-photon emission computed tomography (MlBI SPECT) at rest and during adenosine provocation, radionuclide angiography, resting echocardiography, low-dose dobutamine echocardiography (in 55 patients), a symptom-limited exercise stress test, and 24-hour Holter recording with ST analysis and analysis of heart rate variability (HRV), 2-8 days after admission to hospital. Follow-up resting MIBI SPECT (71 patients) and resting echocardiography (49 patients) were performed 6 and 18 months later, respectively. One-year end-points were death, reinfarction and revascularisation. Seven patients died and another seven had a non-fatal reinfarction (hard events), and 23 patients underwent revascularisation. Risk for death: Only a history of previous myocardial infarction (p=0.0003), an ejection fraction below 40% (p=0.0002), failure to resolve >50% of ST elevation at 90 minutes (p=0.0001), and being unable to perform an exercise test (p=0.0004) differentiated between the patients who died and the survivors. Risk for reinfarction: No studied clinical variables or methods predicted reinfarction. Prediction of need for revascularisation: A positive symptom-limited exercise stress test (p=0.027), ST depressions on Holter recording (p=0.04), and reversibility on myocardial perfusion scintigraphy (p=0.029) predicted a need for revascularisation. Prediction of myocardial recovery: Low-dose dobutamine echocardiography predicted left ventricular functional improvement (p<0.001) and recovery of myocardial perfusion (p<0.001) at follow-up. In addition, exercise-induced ST-segment elevation in the infarct area was associated with myocardial viability (p=0.01). MIBI SPECT failed to detect myocardial viability. In conclusion, clinical risk assessment, the symptom-limited exercise test, and estimation of left ventricular function by echocardiography or nuclear angiography appear to have preserved their prognostic value compared with that in the pre-thrombolytic era. Additional non-invasive investigations such as adenosine MIBI SPECT, analysis of HRV and Holter monitoring seem to have limited additional value for clinical risk stratification. Low-dose dobutamine echocardiography may be used to assess myocardial viability after thrombolytic therapy.

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