Elsevier

Journal of Electrocardiology

Volume 40, Issue 1, January–February 2007, Pages 101-109
Journal of Electrocardiology

Clinical Diagnosis
The value of the electrocardiogram in risk assessment in primary prevention: Experience from the West of Scotland Coronary Prevention Study

https://doi.org/10.1016/j.jelectrocard.2006.05.003Get rights and content

Abstract

Electrocardiograms (ECGs) were recorded at baseline, annually thereafter, and at run-out in the West of Scotland Coronary Prevention Study to which 6595 men aged from 45 to 65 years on entry were recruited. The baseline ECGs were analyzed with respect to (a) the primary end point of the study, namely, fatal or nonfatal myocardial infarction (MI) and (b) all-cause mortality. In addition, incident MIs were reviewed to determine those detected by ECG only. Heart rate, indexed left ventricular mass, frontal T axis, and T amplitude in lead I were all significantly predictive with respect to the primary end point in a multivariate analysis. With respect to all-cause mortality, minor ST-T changes, 10-second heart rate variability, and frontal T axis were similarly predictive. Of 355 incident MIs, 47.3% were silent or unrecognized and detected by ECG only. A simple ECG-based risk prediction equation for fatal and nonfatal MI is introduced.

Introduction

The electrocardiogram (ECG) has been of major interest in many epidemiological and clinical trials1, 2, 3, 4, 5, 6 in which the prognostic value of ECG abnormalities has been assessed, often with respect to classification of the ECG based on the Minnesota Code.7 In most of such studies, the Minnesota Coding has been undertaken manually.

There have been both primary and secondary intervention trials aimed at reducing the risk of fatal or nonfatal myocardial infarction (MI) in patients with raised lipids, notably the LIPID Research Clinic Trial,2 the Helsinki Heart Study,3 and the 4S Trial.4 Electrocardiographic data from these studies are limited, and after the completion of the West of Scotland Coronary Prevention Study (WOSCOPS),5 the opportunity has arisen to review the electrocardiographic data, particularly with a view to studying the ECG as a risk factor and to assessing the benefits of intervention with respect to baseline electrocardiographic findings.

In addition, on account of the fully automated techniques of ECG recording and measurement used during WOSCOPS, there was a further unique opportunity to consider relatively recently developed measures of interest, such as QT dispersion, in the setting of primary prevention.

In the WOSCOPS, 6595 men with moderate hyperlipidemia and no previous history of MI were randomized to treatment either by placebo or pravastatin 40 mg nocte. Subjects were followed up for a mean of 4.9 years, and all events, cardiovascular or otherwise, were recorded over the period of the trial. Full details of the study are available elsewhere.5, 8 The principal finding was a 31% reduction in risk of definite coronary heart disease (CHD), death, or nonfatal MI, that is, the primary end point, in the treated group compared with the placebo group.

Twelve-lead electrocardiography was used throughout the study, and this article reviews the methodology, presents the ECG findings in the study, and assesses the value of ECG recording in primary prevention. Some preliminary observations have already been reported in this journal.9

Section snippets

Methods

Twelve-lead ECGs were recorded using a computer-assisted electrocardiograph, that is, the SICARD 440, in which the Glasgow ECG interpretation program resided.10 The ECGs were collected initially in more than 45 screening centers in the West of Scotland and, latterly, in more than 20 trial centers and transmitted in digital form by telephone to the ECG Core Laboratory in the former Department of Medical Cardiology in the Glasgow Royal Infirmary. A 12-lead interpretation was provided at the

Minor ECG changes

The presence of Minnesota Codes 4-2, 4-3, 5-2, and 5-3 either singly or in combination was regarded as constituting minor ECG changes.

Left ventricular hypertrophy

Probable left ventricular hypertrophy (LVH) according to Minnesota Code was a combination of 3-1 or 3-3 plus any of 4-2, 4-3, 5-2, or 5-3 at baseline. Possible LVH was defined as 3-1 or 3-3 without minor ST-T changes, as defined above.

Indexed left ventricular (LV) mass was estimated in 2 ways. The first was based on the equation of Rautaharju et al,13 namely for

Statistical methods

Baseline data were tabulated for the 2 randomized treatment groups (pravastatin and placebo). Incident ECG findings were calculated by serial comparison of the baseline ECG with the last available postrandomization ECG and compared between the 2 groups using odds ratios and 95% confidence intervals (CIs) with associated P values. New ST- and T-wave abnormalities were likewise compared in the subgroup free from such abnormalities at baseline. Incident nonfatal MIs, characterized as either

Baseline data

Table 1 lists the baseline electrocardiographic characteristics by randomized treatment group of the 6595 men in the study. As expected, there are no appreciable differences with respect to ECG findings at baseline between the 2 groups.

Incident findings

Table 2 provides details of the incidence of atrial fibrillation, new-onset bundle-branch block, and ischemic changes, including new code 1 of the Minnesota Code suggestive of MI, by treatment group, for the 88% of randomized subjects who had at least 1

Methodology

The use of automated techniques for a large primary prevention trial has been justified with the interesting new data that have emerged. The alternative of manually coding or measuring ECGs when a total of approximately 33 000 recordings was involved over the 7 years of the study would have been extremely difficult, particularly for assessment of measurements such as QT dispersion, SDNN, and LV mass, and for detection of any change in PR or QT interval between baseline and the end of the study.

Conclusion

The multivariate analyses have shown that the ECG contains prognostic information independent of the clinical variables. It therefore seems that there might be merit in advocating that the ECG be recorded as part of a routine assessment of cardiovascular risk in any patient, particularly men 45 years and older. However, although the ECG covariates are statistically significant in terms of independent or additional prognostic value, the ROC analysis shows that they do not lead to much improved

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