Intraventricular conduction delay: a prognostic marker in chronic heart failure

Abstract

Chronic heart failure (CHF) is associated with high mortality, and there are several established clinical and laboratory parameters that predict mortality in CHF. The purpose of this study was (a) to identify the best ECG parameter that predicts mortality, (b) to evaluate the prognostic marker of ECG against well-established indicators of prognosis. Relevant data from 241 CHF patients were analysed retrospectively. Cardiopulmonary exercise testing and radionuclide ventriculogram were also performed where possible. The mean follow-up period was 31 months. On univariate analysis by the Cox proportional Hazard method, intraventricular conduction delay (IVCD) [P<0.0001, hazard ratio 1.017 (l.011–1.024)] and QTc [P<0.0001, hazard ratio l.012 (1.006–1.017)] were identified as predictors of mortality. On bivariate analysis, IVCD and MVO2 were better predictors when combined together. A model based on multivariate analysis showed that IVCD, MVO2 and left ventricular ejection fraction (LVEF) were the best predictors of mortality. The addition of plasma sodium, age and NYHA class had no added benefit on the predictive power of the model. Further analysis of IVCD and QTc showed that, for different cut-off values, IVCD is better than QTc, and that there is a graded increase in mortality with increasing value of IVCD. We have found that IVCD is an important ECG predictor of prognosis in patients with CHF.

Introduction

The prevalence of chronic heart failure (CHF) has increased in the past few decades due to ageing of the population and improved survival from myocardial infarction. It remains a condition with a high mortality rate. The Framingham study showed a 10% annual mortality rate in patients with newly diagnosed heart failure [1]. Once heart failure was detected, only 25% of men and 38% of women were alive at five years, reflecting a six–seven-times higher mortality rate than that of the general population of same age [2]. After an acute myocardial infarction, heart failure carries an even worse prognosis [3]. The poor prognosis of heart failure was confirmed in a study in Rochester, MN, with only a 66% one-year survival after diagnosis [4]. For patients with CHF, the benefits of symptomatic improvement achieved by medical therapy are often terminated by sudden, unexpected death [5]. Attempts to identify high risk subgroups of CHF patients have met with limited success [6], [7], [8].

There has been much interest in the clinical and investigative features predictive of outcome in patients with CHF [9]. Of the numerous variables that have been studied [10], peak oxygen consumption or total exercise time, right and left ventricular ejection fractions, pulmonary capillary wedge pressure, the presence of ventricular arrhythmias, levels of catecholamines, atrial peptides and plasma sodium are all accepted as important predictors of prognosis in patients with CHF [11], [12], [13], [14], [15], [16]. The cachectic state has also recently been described as a strong independent factor for mortality in patients with CHF [17]. Echocardiographic variables have been extensively studied in patients with dilated cardiomyopathy for the evaluation of their association with symptoms and mortality [18].

Houghton et al. [19] showed the importance of ECG in diagnosing heart failure in general practice. Fewer studies have examined ECG parameters as prognostic indicators in CHF. Most that have, have looked for axis, heart rate, PR interval, P wave, ST segment or T-wave features. There are very few studies on other parameters of the ECG, such as QT, QTc or QRS duration. The available studies have small numbers of patients and, as a result, it is difficult to derive definitive conclusions [20], [21]. The combination of increasing PR interval and longer QRS duration appears to be a marker of high risk in patients with dilated cardiomyopathy [22], however, a number of questions remain unanswered. The present study aimed to identify the prognostic significance of simple ECG parameters in a large single-centre population of consecutive patients with chronic heart failure.