Munich, Germany - Impaired heart-rate deceleration capacity, which can be measured with a Holter-based test, is a powerful predictor of mortality after myocardial infarction and is more accurate than left ventricular ejection fraction (LVEF) and the conventional measures of heart-rate variability, a new study shows.

The study, published in the May 20, 2006 issue of the Lancet, was conducted by a team led by Drs Axel Bauer (Deutsches Herzzentrum, Munich, Germany) and Georg Schmidt (Munich University of Technology, Munich, Germany).

They explain that in high-risk survivors of MI, mortality can be greatly reduced by implantation of an ICD and that poor LVEF is generally used to predict risk. However, many patients without reduced LVEF are still dying post-MI, and a more accurate method of risk prediction is needed. Heart-rate variability has been suggested as a possible candidate, given that decreased heart-rate variability is associated with a poor prognosis. However, they point out that heart-rate variability is affected by both vagal and sympathetic modulation of the sinus node, and evidence suggests that it is a fall in vagal activity that increases the risk of death, but overall measures of heart-rate variability do not distinguish between vagal and sympathetic effects.

They suggest that an approximate distinction of vagal and sympathetic effects might be made possible by separate assessment of deceleration-related and acceleration-related heart-rate variability and that the deceleration capacity of the heart rate provides a measure of cardiac vagal modulations and therefore should be an important prognostic marker.

To test this hypothesis, the researchers analyzed heart-rate deceleration capacity derived from 24-hour Holter measurements in 1455 patients from a German MI study, and they found that this was indeed a stronger predictor of mortality than LVEF or the measures for heart-rate variability and acceleration capacity derived from the same Holter test.

They then validated these results in two additional post-MI studies including more than 600 patients each, one conducted in London and one in Finland, and found that mortality rates were enhanced fivefold in individuals with low heart-rate deceleration capacity.

Long-term mortality rates varied between the three studies from 5% to 13%, but cardiac deceleration capacity correlated well with long-term risk in both low-risk and high-risk patients.

The researchers write: "Our results clearly show that there are large differences in risk assessment derived from heart-rate acceleration and deceleration." Noting that the physiological mechanisms responsible for acceleration and deceleration of heart rate are probably different, they say that their findings show that pathologies that slow the heart down are more clinically important than those that speed it up.

In an interview with heartwire, Schmidt explained that his team has developed a computer program that can be used with Holter machines to calculate deceleration capacity, and they are talking to various companies selling Holter machines about commercialization of this technology. "We have shown in three studies that the deceleration capacity of the heart is better than all other long-term ECG parameters in predicting risk of death post-MI. I have no doubt that this finding is correct, but people will probably want to see confirmation from other groups," he commented.

Schmidt pointed out that this technology would be particularly useful for detecting patients at high risk of death post-MI who do not have a reduced ejection fraction. His team has conducted a study in 4300 MI patients in Germany who were followed for up to 10 years. There were a total of 350 deaths, but only 70 of these were in patients with reduced left ventricular function. But when they used deceleration capacity, they identified another 60 to 70 patients who died. "Using this method alongside reduced left ventricular function therefore doubles the sensitivity, without losing predictive accuracy," he added.

In the paper, the researchers conclude: "The high consistency of the deceleration-capacity-based tests, together with the simplicity of the computational algorithm, suggest that the deceleration-capacity index is suitable as an inexpensive, easily obtainable, and noninvasive postinfarction screening method for use in the early identification of low-risk patients in whom further diagnostic workout is not warranted and in the improved selection of those who are likely to benefit from prophylactic interventions."

In an accompanying editorial, Dr Sami Viskin (Tel Aviv Sourasky Medical Centre, Israel) points out that tests with good performance during research studies do not always get the role they deserve in clinical practice. And he notes that heart-rate variability has been shown to be a stronger predictor of mortality after MI than the presence of arrhythmias in a Holter recording, but most referrals for consideration of ICD insertion seen at arrhythmia clinics still follow the discovery of asymptomatic ventricular arrhythmias—not impaired heart-rate variability—on 24-hour continuous cardiac monitoring.

In response, Schmidt commented to heartwire that although heart-rate variability is a predictor of risk, it does not give as good a risk estimate as deceleration capacity and it may not be well used because it needs to be evaluated on a 24-hour Holter. "I believe deceleration capacity will be used when people appreciate our results. It is a much better predictor than heart-rate variability, and it might be possible to get a reliable reading in much shorter times than 24 hours. In the current paper, we used 24-hour monitoring and we saw beautiful data, but we have some other studies suggesting it can work with just 30 minutes of monitoring, although this needs confirmation."

Viskin also cautions that the ultimate goal of risk stratification is not merely to identify individuals at high risk of dying but to detect those who are particularly likely to benefit from a specific intervention such as an ICD, and this can be ascertained only from randomized clinical trials of ICD insertion.