Background It has been well recognized that ST segment depression(STD) could occur on non-infarcted leads on the acute myocardial infarction (AMI) patient’s ECG. However, the underlying mechanism and the significance of such ST segment depression keep unclear. It could be explained by a mirror reflection mechanism in some patients, but in some patients it reflects the concurrent ischemia or infarction, which predict high probability of adverse cardiac events and poor long term prognosis. In general, ST depression showed on leads V1-V3 indicates ischemia of posterior and lateral-posterior wall; ST depression showed on leads V4-V6 indicates left anterior descending(LAD) disease or multiple vessel disease; ST segment depression showed on inferior leads indicates proximal disease of left anterior descending; ST segments change showed on leads of high-lateral and inferior wall are usually reciprocal. So far there is no study to systematically address the significance of the ST segment depression and the influence of coronary heart disease(CHD) risk factors on ST segment depression in AMI patients. Objective To investigate the clinical significance of ST segment depression in AMI patients. Methods From September of 1998 to December of 1999, a total of 55 AMI patients, including 39 males, 16 females, with an average age of 61.9±10.2 (37-87), were enrolled in the study. Patten, magnitude, occurring time, lasting time, time concordance with ST segment elevation, concurrent T wave change, and occurring frequencies of ST segment depression were recorded from electrocardiogram(ECG); Consecutive bedside echocardiograms(UCGs) were performed within 24 hours of AMI and two weeks later; Adverse cardiac events during hospitalization were recorded. The associations of the ST segment depression with ventricular wall movement and adverse cardiac events were analyzed in three groups: Group 1: without ST segment depression (n=11); Group 2: ST segment depression lasted less than 24 hours (n=34); Group 3: ST segment depression lasted longer than 24 hours (n=10). Also, subgroup analyses were performed according to hypertension and diabetes. Results 1，Among the 55 patients, the incidence of ST segment depression on non-infarcted leads is 80%. The average occurring time of ST segment depression is 3 hours after the onset AMI, with the range of 10 minutes to 21 hours; the average lasting time of ST segment depression is four hours, with the range of 30 minutes to 14 days; the average magnitude of ST segment depression is 1.8mm, with the range of 0.5mm to 8mm. There is no statistical significance between patients in Group 2 and in Group 3 regarding to the magnitude of ST segment depression (1.9mm vs 1.5mm); 2，ST segment depression on non-infarcted area during acute myocardial infarction may occur on leads I , aVL, leads II, III, aVF, leads V1 toV3, leads V4-V6, and the incidence of ST segment depression on the above groups are 29.6%，24.7%，22.2%，23.5%，respectively. The detection rate of segmental wall movement abnormality (SWMA) by UCG on ventricular walls corresponding to leads II、III、aVF and V4-V6 in ECG is higher than those corresponding to leads I, aVL, and V1-V3; 3，Among the forty-four patients with ST segment depression, the incidence of STD and STE synchronization is high(77.3%), and the incidence of SWMA in patients with STD and STE synchronization is lower than that without STD and STE synchronization; 4， The admission time of group 1 is longer than that of the other two groups(19.8 hours in Group 1，6.5 hours in Group 2，and 5.1 hours in Group 3，P=0.002); 5，The incidence of HBP or DM、the peak CK and CK-MB、multiple coronary artery lesion、SWMA determined by UCG and some complications related with prognosis, such as arrhythmia、post-infarction angina pectoris、re-infarction、dysfunction of papillary muscle and hypotension increases from Group 1 to Group 3; 6，The occurrence of SWMA on the ventricular wall corresponding to the non-infarcted area that showed STD is influenced neither by hypertension, nor by diabetes. In patients with hypertension, the detection rate of SWMA is highest in group 2. In patients without HBP, the detection rate of SWMA increases from Group 1 to Group 3. This phenomenon is also seen in patients with DM or not. Conclusion ST segment depression on non-infarcted leads in ECG is a common phenomenon during acute myocardial infarction, it is probably a process of ECG evolvement during AMI. Persisting ST segment depression on non- infracted area indicates concurrent ischemia or infarction, so does ST segment depression mismatched with ST segment elevation. SWMA determined by bedside UCG is helpful to analyze the significance of ST segment depression during acute myocardial infarction. ST segment depression during acute myocardial infarction implies poor prognosis, and hypertension and diabetes mellitus should be considered simultaneously.

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