Elsevier

American Heart Journal

Volume 140, Issue 2, August 2000, Pages 221-226
American Heart Journal

Acute Ischemic Heart Disease
Strict reliance on a computer algorithm or measurable ST segment criteria may lead to errors in thrombolytic therapy eligibility,☆☆

https://doi.org/10.1067/mhj.2000.108240Get rights and content

Abstract

Background There is accumulating evidence that thrombolytic therapy is underused among eligible patients with acute myocardial infarction. We sought to determine whether potential errors in electrocardiographic diagnosis might be a contributing factor. Methods Seventy-five electrocardiograms were interpreted on 2 separate occasions by 3 cardiologists. Two criteria were compared for thrombolysis eligibility: (1) measurement of ≥1 mm ST-segment elevation in 2 contiguous leads (measured) and (2) criterion 1 plus the subjective opinion that the changes represented acute transmural injury (interpretive). The results were compared with computerized interpretations by the Marquette 12SL system. Results Raw agreement and agreement corrected for chance between raters for both criteria were excellent and tended to be better for interpretive compared with measured criteria (κ = 0.89 vs 0.78, respectively). Strict reliance on measured electrocardiographic criteria alone would have resulted in overuse of thrombolysis among all 3 raters. Based on the consensus opinion, the absolute overuse of thrombolysis would have been approximately 15% (P <.0034). The computer algorithm had a specificity of 100% and a sensitivity of 61.5%. Reliance on the computerized interpretation alone would have lead to underuse of thrombolytic therapy compared with consensus opinion (21.3% vs 34.6%; P <.005). Conclusion Agreement for suspected acute myocardial infarction tended to be better when the appearance of the ST segments was added to measurable ST elevation criteria. Strict reliance on measurable criteria may lead to the inappropriate overuse of thrombolysis. Although the Marquette 12SL system has excellent specificity, it has poor sensitivity for the diagnosis of thrombolysis-eligible AMI. Reliance on computerized electrocardiographic interpretation would lead to the inappropriate underuse of thrombolytic therapy in situations in which qualifying electrocardiographic criteria are actually met. (Am Heart J 2000;140:221-6.)

Section snippets

Methods

Seventy-five ECGs were independently interpreted by 3 cardiologists on 2 occasions (within 7 days) to study ECG interpretation in the setting of AMI. The ECGs were selected among patients in our cardiac care unit or ward and were roughly evenly divided among (1) normal, (2) those showing evidence of acute transmural injury, or (3) those showing other ST-segment or T-wave abnormalities. The latter included ischemic ST-segment depression and/or T-wave inversion and mimics of acute transmural

Observer variability

Raw agreement between raters regarding the presence of ≥1 mm ST elevation (measured criteria) or thrombolysis-eligible AMI based on interpretive criteria was excellent (Table I).Agreement corrected for chance (κ) was good to excellent and tended to be better for interpretive compared with measured criteria (κ = 0.89 vs 0.78, respectively; P =.13).

Intraobserver variability was substantial for each reader (κ = 0.67, 0.69, and 0.71) but lower than the interobserver variability for each criteria (

Discussion

At present, a carefully performed patient history and clinical examination coupled with an accurate ECG interpretation are still the best method of diagnosing a thrombolysis-eligible AMI candidate. Our study demonstrates that human estimation of quantifiable parameters alone, such as the amount of ST-segment elevation, are insufficient for deciding thrombolytic therapy eligibility because there are many ECG mimics of AMI. Our results are in keeping with those of Otto and Aufderheide,14 who

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    Dr Dawdy was supported by the Victoria Hospital Research and Development Fund.

    ☆☆

    Reprint requests: David Massel, MD, FRCPC, Medical Director, Cardiac Care Unit, London Health Sciences Centre, Room 205, Colborne Building, Victoria Campus, 375 South St, London, Ontario, Canada N6A 4G5. E-mail: [email protected]

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