Q J Med 2000; 93: 701-702
© 2000 Association of Physicians
Correspondence |
Silent myocardial ischaemia after coronary artery bypass graft
Thrombosis Research Institute Central Middlesex Hospital London
Sir,
Most episodes of myocardial ischaemia in patients with known coronary artery disease (CHD) are asymptomatic.1 Silent myocardial ischaemia (SMI) is an important predictor of adverse outcome in patients with proven coronary-artery disease.2
Beta-blockers are effective in suppressing ischaemia, and improve clinical outcome in patients with coronary artery disease.3 At present, it is common practice to stop treatment with ß-blockers in clinically asymptomatic patients after CABG, although the incidence of SMI after CABG is not known.
We examined 19 asymptomatic CHD patients after CABG; therapy with ß-blocker was stopped in all after surgery. All these patients underwent dobutamine stress echocardiography. All patients had a history of myocardial infarction or evidence of mildly impaired left ventricular function at rest as assessed by cardiac catheterization.
Dobutamine was infused intravenously at an incremental regimen of 5, 10, 15, 20, 30, and 40 µg/kg/min every 5 min for the first two doses and 3 min thereafter. Atropine 300–600 µg intravenously was given at the end of the 40 µg/kg/min dose if target heart rate (i.e. 85% predicted maximum) was not achieved. The test was terminated when the heart rate reached 85% of the age-predicted maximum heart rate. Two-dimensional echocardiograms were obtained at baseline, 5 µg/kg/min, peak dose, and during recovery. Images were digitized in continuous loop and placed in quad screen format for review and analysis. The left ventricle was divided into 16 segments according to the recommendations of the American Society of Echocardiography.4 All echocardiographic recordings were reviewed by one independent observer who was blinded to the patients' clinical data.
Regional myocardial contractile function was graded as normal, hypokinetic, akinetic, or dyskinetic, in each myocardial segment, with reference to systolic wall thickening rather than endocardial motion. A normal response to dobutamine was a progressive increase in systolic myocardial thickening, wall motion, or both, during the sequential stages of dobutamine infusion. An abnormal echocardiographic stress test result was defined as one showing the development of a new or worsening stress-induced regional wall motion abnormality compared to baseline.
The clinical characteristics of the 19 patients are listed in Table 1
. Abnormal DSE studies occurred in 3/19 patients (16%; 95%CI 3–40%), thus, in the 19 CHD patients that underwent CABG, the incidence of SMI was 16%. This incidence seems to be lower than that after balloon angioplasty and stenting procedures.5 Therapeutic approaches specifically targeted at reducing total ischaemic burden include pharmacological therapy and myocardial revascularization. The Atenolol Silent Ischemia Study Trial (ASIST) was the first randomized placebo-controlled trial showing the favourable effects of ß-blocker therapy in reducing the frequency of asymptomatic ischaemia and improving clinical outcome.3
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Our study was limited by the size of the sample and thus, neither the significance of SMI in relation to adverse clinical outcome nor the role of ß-blockers in the prevention of SMI could be evaluated. To assess more confidently the frequency of SMI after CABG and to define the prognostic significance, larger studies are warranted. On the basis of these data, it can be concluded that asymptomatic CABG patients should be evaluated to rule out SMI and therefore improve the long-term clinical outcome.
References
1. Epstein SE, Quyyumi A, Bonow RO. Myocardial ischemia—silent or symptomatic. N Engl J Med1998; 318:1038–42.[Web of Science][Medline]
2.
Deedwania PC, Carbajal EV. Silent ischemia during daily life is an independent predictor of mortality in stable angina. Circulation1990; 81:748–56.
3.
Pepine CJ, Chon PF, Deedwania PC, Gibson RS, Handberg E, Hill J, Miller E, Marks RG, Thadani U. Effect of treatment on outcome in mildly symptomatic patients with ischemia during daily life. The Atenolol Silent Ischemia Study. Circulation1994; 90:762–8.
4. American Society of Echocardiography Committee on Standards, Subcommittee on Quantification of Two Dimensional Echocardiograms. Recommendations for the left ventricle by two dimensional echocardiography. J Am Soc Echocardiogr1989; 2:358–67.[Medline]
5. Kathiresan S, Jordan MK, Gimelli G, Lopez-Cuellar J, Madhi N, Jang IK. Frequency of silent myocardial ischemia following coronary stenting. Am J Cardiol1999; 84:930–2.[Web of Science][Medline]
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