Clinically Silent Electrocardiographic Abnormalities and Risk of Primary Cardiac Arrest Among Hypertensive Patients

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Abstract
Background Whether continuous ECG indexes that reflect the severity of left ventricular hypertrophy (LVHI), myocardial injury (CIIS), and QT-interval prolongation (QTI) are associated with the risk of primary cardiac arrest among hypertensive patients, independent of conventional binary ECG criteria, remains unknown. Methods and Results We conducted a population-based case-control study among patients who were free of clinically recognized heart disease and who received care at a health maintenance organization. Cases (n=131) were treated hypertensive patients who had had a primary cardiac arrest between 1977 and 1990. Controls (n=562) were a stratified random sample of treated hypertensive patients. Resting ECGs were reviewed to estimate the severity of left ventricular hypertrophy, myocardial injury, and QT-interval prolongation on the basis of the algorithms of the Novacode ECG classification system. After adjustment for other risk factors and binary ECG criteria for the abnormalities, the LVHI, CIIS, and QTI scores were directly related to the risk of primary cardiac arrest. In a comparison of the 80th with the 20th percentile score for the LVHI, the risk was increased 40% (odds ratio, 1.4; 95% CI, 1.0 to 2.0); for the CIIS, the risk was increased 70% (odds ratio, 1.7; 95% CI, 1.2 to 2.5); and for the QTI, the risk was increased 80% (odds ratio, 1.8; 95% CI, 1.3 to 2.7). Conclusions Our findings suggest that continuous ECG indexes that reflect left ventricular hypertrophy, myocardial injury, and QT-interval prolongation are directly related to the risk of primary cardiac arrest among hypertensive patients without clinically recognized heart disease. Binary ECG criteria may underestimate the prognostic importance of these pathophysiological abnormalities.