Out-of-hospital electrocardiography (ECG) is the basis for identifying patients with suspected acute myocardial infarction (AMI) who should receive early thrombolytic therapy before arriving at the hospital. The diagnostic accuracy of out-of-hospital ECG in identifying AMI and acute coronary insufficiency has been reported in several studies. Ioannidis and associates conducted a meta-analysis of studies on the use of out-of-hospital ECG in identifying AMI to clarify diagnostic accuracy in this setting and evaluate the clinical effect of out-of-hospital thrombolytic therapy compared with hospital initiation of thrombolysis.
Eight studies addressed diagnostic accuracy for AMI based on ECG interpretation, while data on the accuracy for acute cardiac ischemia were included in five studies. Three studies evaluated the accuracy of the data of specific ECG changes. The out-of-hospital ECG had diagnostic accuracy for AMI and acute cardiac ischemia ACI similar to that of a standard ECG. The diagnostic odds ratio was high for AMI (excellent diagnostic accuracy) and lower for acute cardiac ischemia (very good diagnostic accuracy). The clinical effect of out-of-hospital ECG was reviewed in terms of the outcomes of time saved, early differences in left ventricular function, hospital mortality, and long-term mortality.
Review of eight studies evaluating the time of onset of symptoms to thrombolysis revealed a significant reduction in the time to treatment (ranging from 20 to 60 minutes) when decisions were made based on an out-of-hospital ECG. Results of five studies indicate no short-term effects on left ventricular function with out-of-hospital thrombolysis, although there was a statistically significant 16 percent reduction in the risk of death (up to 60 days after hospital admission) with earlier thrombolysis. Long-term effects on mortality are less certain.
The authors conclude that using an out-of-hospital ECG with a protocol for thrombolysis may decrease the time to treatment by up to one hour. Out-of-hospital thrombolysis results in a small but significant decrease in early mortality with one life saved in the short term for every 60 patients who receive out-of-hospital treatment rather than delaying treatment until reaching the hospital. Long-term survival benefits are less clear.