Longer heartbeats could shorten lives
Hearts with longer intervals between each ventricular contraction and relaxation face an increased risk of death. But probably only if you are male.
Men with long QT intervals have a greater risk of premature death, according to a recent Norwegian study.
QT intervals are monitored in routine heart examinations − in electrocardiograms (ECGs) − and represent the time between one of the contractions of ventricle and the end of its relaxation phase.
The likelihood of dying from nearly all causes increases when the length of this interval goes up, but surprisingly not the risk of dying of a heart attack.
This has been reported by the Department of Community Medicine at the University of Tromsø (UiT).
Risk of serious heart flicker
Professor Maja-Lisa Løchen of the UiT’s Department of Community Medicine headed the work and Resident Physician Haakon Lindekleiv was the first author of the study.
“We already knew that a prolonged QT interval can be a hazard for persons with a rare, hereditary disease,” says Løchen.
“The scant few (0.03 percent of the population) who have a genetic prolonged QT interval risk serious ventricular fibrillation and sudden death.”
Little known about risk for majority
Less is known about the risk this comprises for others. Some studies indicate an increased risk of coronary infarct; others don’t – as is the case with the recent Norwegian study.
Doctors can’t say how dangerous an extended QT interval is among the general population.
"Actually, a lot of people have this condition, without us being to say much about what it entails,” adds Løchen. "No routine ECGs are taken of the entire population. So it’s a risk factor we are still researching."
The study states that five percent of the Norwegian population have a prolonged QT interval and nine percent are on the borderline.
No clinical consequences yet
The Norwegian researchers point out that the issue of a link between QT intervals and cardiovascular disease is controversial. But their results contribute to the undermining of arguments for such a link.
Even though the new study reports a higher general risk of death among men with a prolonged QT interval, further research on the subject is required before such findings can have any consequences on how patients are examined and treated.
Løchen explains that the discovery has no clinical consequences yet. This is still a research area and they don’t want to cause undue alarm.
“But we show that the condition has consequences for people’s health and among other things we’ll look into why within a 20-year period there’s a gender difference with regard to the risk of death.”
The new work was recently published in the Journal of Cardiovascular Electrophysiology, and it's based on a large survey.
The research is part of the Tromsø Study from 1986-87 and includes electronic ECG records stretching back to 1986. It includes a follow-up period of 20 years with regard to mortality rates and heart attacks.
More specifically, it encompasses 15,558 ECGs of women and men aged 20 to 60.
In the 1980s, electronic ECGs were still uncommon and it was also unusual to store the data. But with the assistance of a local IT firm Løchen has retained the records.
Not necessarily something to treat
If a general practitioner deems it necessary after an examination, he or she will refer the patient to a specialist.
“The doctor will look at an ECG to see if the interval is too long and diagnose it on an individual basis, without necessarily having to initiate any treatment.
“We simply need to know more about the QT interval’s significance for our health,” says Løchen.
Translated by: Glenn Ostling
- QT Interval and the Risk of Myocardial Infarction and All-Cause Death: A Cohort Study. Haakon Lindekleiv, Tom Wilsgaard, Peter W. Macfarlane, Maja-Lisa Løchen, Article first published online: 17 APR 2012. DOI: 10.1111/j.1540-8167.2012.02308.x abstract.