Exercise caution when using treadmill ECGs for angina assessment

Prompt assessment and risk stratification is fundamental to the early management of patients presenting for the first time with suspected angina. Within the setting of rapid access chest pain clinics (RACPC), risk stratification is traditionally achieved by history taking, examination, resting ECG and exercise ECG (ex-ECG). However, it remains unclear whether the inclusion of resting and exercise ECG adds incrementally to the prognostic value achieved by history taking and physical examination alone.

In order to address this question, Sekhri and colleagues investigated 8,176 consecutive ambulatory patients who attended RACPC in the UK with symptoms consistent with new-onset angina, thereby avoiding possible selection bias encountered when including patients with previously documented coronary heart disease. All subjects received a basic clinical assessment, which included history and examination, and resting ECG. 4,957 individuals went on to have ex-ECG, with ex-ECG summary data available in 4,848 and detailed ex-ECG data available in 1,422. The main outcome measure was a composite end-point of fatal and non-fatal coronary heart disease (CHD) over a median follow-up period of 2.46 years.

Investigators found that typical chest pain, abnormalities of the resting ECG and ex-ECG were associated with adverse outcomes; probability for primary outcome at 3 years 16%, 15% and 19%, respectively, compared with 3, 5, and 9% for patients with non-specific chest pain, normal resting and ex-ECGs respectively. Importantly, however, 47% (n=166) of the events recorded during follow-up occurred in patients with ‘normal’ ex-ECGs, which highlights the limitations of ex-ECGs for risk assessment.

Indeed, evaluation of the incremental benefit of ex-ECGs in addition to clinical assessment provided disappointing results particularly among subjects with an intermediate pre-test probability for CHD, the group in which the ex-ECG is most useful for diagnostic purposes. Among these subjects, comparison of the receiver operating curve (ROC) for basic clinical assessment alone and for resting ECGs demonstrated poor discrimination. For ex-ECG only marginal increases in the C statistic were observed, which represented a trivial increment in prognostic value; with ex-ECG iterations the C statistic (95% CI) for the basic clinical assessment model increased in the summary ex-ECG subset from 0.69 (0.65 to 0.73) to 0.74 (0.70 to 0.78) and in the detailed ex-ECG subset from 0.69 (0.62 to 0.77) to 0.76 (0.70 to 0.82).

Therefore this study supports the view that the clinical assessment holds virtually all the prognostic information provided by the resting and ex-ECG. The limited incremental value of resting and ex-ECG data re-emphasises the importance of taking a detailed history and performing a thorough physical examination, and that caution must be shown when using ex-ECGs for the risk stratification of patients presenting with angina.

  • Sekhri N, Feder GS, Junghans C et al.  Incremental prognostic value if the exercise electrocardiogram in the initial assessment of patients with suspected angina: cohort study.  BMJ 2008;337:a2240

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