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[Problems of electrocardiographic diagnosis of occlusion of the left circumflex coronary artery].

BACKGROUND AND OBJECTIVE
The electrocardiographic diagnosis of posterior myocardial infarction is difficult. It was the objective of the present study to evaluate ST-segment changes in angiographically documented occlusion of the left RCX in the setting of an acute myocardial infarction and to analyse the value of the posterior chest leads V(7)-V(9).


PATIENTS AND METHODS
Data of 120 patients (88 males, on average 61+/-13 years old) with an acute myocardial infarction and angiographically proven occlusion of the left circumflex artery were included in the study. Mean time of pain onset to ECG recording was 5.5 +/- 2.8 hours. The ECGs were analysed for ST-segment changes of > or = 1 mm in two contiguous leads in surface leads I-aVF, > or = 2 mm in the precordial leads V(1)-V(6), and > or = 1 mm in right precordial (V(3)R-V(6)R) and posterior (V(7)-V(9)) leads. These additional leads were recorded only in a subgroup of 36 patients. Maximal creatine kinase activity was determined as a measure of infarct size.


RESULTS
Standard leads I-V(6) showed ST-segment elevation in 55 of 120 patients (46 %). In the subgroup of patients with extended chest leads 61 % (11/36) had significant ST-segment elevation, whereas isolated ST-segment elevation in the posterior leads occurred in 8 % (3/36). ST-segment depression in the standard leads was observed in 73 of the 120 patients (54 %), and isolated ST-segment depression was seen in 31 patients (26 %). No significant ST-segment changes in the standard leads were found in 34 patients (28 %). Maximum CK values were not significantly different among the three groups (1107 +/- 815 IU/l vs 953 +/- 651 IU/l vs 816 +/- 553 IU/l; (P = 0.447).


CONCLUSION
These findings confirm that the sensitivity of the standard ECG leads is less than 50 % in angiographically documented occlusion of the left RCX. The extended posterior chest leads (V(7)-V(9)) improve sensitivity only marginally (by 8 %). Isolated ST-segment depression or no significant ST-segment depression in the standard leads was observed in 26 % and 28 % respectively. The infarct size - as measured by maximum CK-values - did not differ among the respective groups.