Editor,—We read the recent important editorial by Lombardi and Mortara with interest,1 and we would like to comment on several points raised.

As the authors state, spectral analysis of short term recordings of heart rate variability (HRV) is of limited value in patients with cardiac failure. Long term recordings in patients with cardiac failure contain a large amount of noise, artefact, ectopic activity, and non-stationary heart rate fluctuations, and spectral measurements are unreliable under these circumstances.2 We believe that studies of HRV in patients with cardiac failure are most reliable when confined to time domain techniques, which are highly reproducible in patients with cardiac disease.3

Most early studies of HRV and risk stratification were small, retrospective, inadequately sized, and most of the patients enrolled had very severe cardiac failure. These patients can be risk stratified by a physician using simple bedside clinical assessment and a stethoscope. The incremental prognostic value provided by additional investigations, such as analysis of HRV, is very limited in patients whose mortality rate may exceed 50% per annum.

The only adequately sized prospective study to evaluate time domain measures of HRV in cardiac failure is the United Kingdom heart failure evaluation and assessment of risk trial (UK-HEART).4Lombardi and Mortara question the general applicability of these results, based on the mean ejection fraction of the patients. Our patients were required to have symptoms plus a low ejection fraction or abnormal chest x ray. We did not exclude patients with heart failure and preserved systolic function, and this may have contributed to the relatively high mean ejection fraction. After entry into the study, ejection fraction was calculated from simple M mode echocardiography. This may underestimate the degree of left ventricular impairment in our study population as M mode echocardiography is unreliable …