Contributed by C. Yap

The write up below summarises the main points of presentations by Prof. Michael Ip and Prof. Alan Wu at a symposium organised by the Singapore Association of Clinical Biochemists and the North American Chinese Clinical Chemists Association on June 17^th, 2000.

The topics were "Atherosclerosis - What Matters Most In Its Etiology" and "Use Of Cardiac Troponin For Risk Stratification In Acute Coronary Syndromes", respectively. Prof. Ip is from MetroHealth Medical Centre, OH, USA and Prof. Alan Wu is from Hartford Hospital, Connecticut, USA.

Myocardial infarction (MI) and ischaemic stroke are acute manifestations of a dynamic and otherwise silent atherothrombotic process in which the etiology has been difficult to establish. Atherosclerosis is closely related to high lipids but there are many other factors which may interact and influence the disease process. Some of these factors include physical inactivity, stress, smoking, hypertension, age and the male sex.

In the United States, serum cholesterol has been monitored closely for the past twenty years and it has been shown that although cholesterol levels have not dropped precipitously, the prevalence of heart attacks has fallen remarkably by over 50%. Other factors which predispose a patient to atherosclerosis include inflammatory mediators, atherogenic components of triglyceride-rich lipoproteins and oxidative damage or stress of the endothelium. In all these aspects there is tremendous opportunity for intervention. Studies have shown that the survival rate following acute myocardial infarction is better for patients who have had dietary counselling on the merits of fish intake. Low dose aspirin is also effective in preventing platelet aggregation in patients with a history of coronary artery disease.

In the United States, about 5% of myocardial infarctions are missed in the Emergency Department because doctors fail to recognise patients at risk. While CKMB and myoglobin are used as markers for diagnosing acute myocardial infarction, the troponins should be used as a marker for risk stratification. Cardiac troponin is not a marker of myocardial infarction but a specific marker for cardiac disease. Outcomes analysis in a variety of clinical conditions has shown that cardiac damage is associated with significant morbidity and mortality as the heart does not adequately regenerate and even minor damage is a bad prognostic sign.

In one study, subjects with silent ischaemia and normal troponin T were given either placebo or heparin. The incidence of infarct was 5% in both groups. Similarly, subjects with high troponin T levels were given either heparin or placebo. The incidence of an acute coronary event was 50% lower in the heparin-treated group in the follow-up period compared to the placebo group. In a second study, the subjects were given either placebo or platelet inhibitor – (Glycoprotein IIb/IIIa inhibitor). In the group with normal troponin levels, there was no difference in outcome between those taking placebo or the drug. However, in the group with elevated troponin levels those taking placebo had a four-fold incidence of cardiovascular disease at 42 days.

Raised troponin levels in cases of acute and chronic renal failure indicate cardiovascular problems that portend poor risk. In a study on dialysis patients, 10 in 30 had increased troponin T levels and 2 in 4 had increased Troponin I levels. After one year, 40% of those positive for troponin T and 25-50 % positive for troponin I had died compared to those with normal troponin levels.

Troponin T is also a long-term prognostic marker for patients post-surgery. Data on 42 patients who had troponin T measured immediately after cardiac bypass surgery showed that the incidence of ischaemia in subsequent months was 0%, 14% and 20% in those whose troponin levels were negative, intermediate and high, respectively.

The cardiotoxic drug doxorubicin which is administered for osteogenic sarcoma and acute lymphoblastic leukemia in children must be monitored and used as little as possible. It is known to have cardio-toxicity as an important side-effect. In a study of 51 children at the Children’s Hospital in Boston, it was shown that troponin T post-operation correlated with surgical severity and magnitude of troponin predicted left ventricular dilatation and wall thinning 9 months later, after the children were cured of lymphocytic disease.

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