Background: Elevation of cardiac biochemical markers and ST segment depression in the electrocardiogram have important roles in the risk stratification of unstable coronary syndromes. We assessed graded duration of acute coronary ischaemia with ST depression versus release of cardiac troponin I (cTnI) and conventional cardiac markers in 15 ischaemic pigs and 11 controls.
Methods: Coronary ischaemia was induced via percutaneous technique by semiinflating an angioplasty balloon in the left circumflex artery. Blood velocity monitored by Doppler was reduced until ST depression > or =0.1 mV was obtained. Among 26 pigs, six controls had jugular vein sheath introduced only, five controls jugular vein and bilateral femoral sheaths, and 15 pigs were divided into three equal groups (n=5) in which ischaemia was maintained for 10, 20 and 30 min, respectively.
Results: Mean blood flow velocity (cm/s) at baseline was 16.3+/-6.5 and was reduced to 4.1+/-3.2 (25% of normal, range 20-29%) during ischaemia. cTnI (microg/l) did not increase in controls but increased from 0.05 to 0.52 (P<0.05) and 0.76 (P<0.05) with 10 and 20 min of ischaemia, and to 30.77 (P<0.05) with 30 min of ischaemia. A rise of myoglobin and conventional cardiac enzymes did not distinguish controls with arterial cut-down from the ischaemia groups.
Conclusion: Release of cTnI depends on the duration of ST depression ischaemia. The critical time for a major release seems to be between 20 and 30 min. Thus, very early intervention in patients with prolonged ST depression ischemia should be focused on in future clinical trials.