Grapefruit juice may promote the development of cardiac arrhythmia in patients at risk suffering from long QT syndrome, a genetic heart disease still unknown to the general public.
Long QT syndrome may affect nearly one in 2,500 births, but few people are aware of this congenital disease or know that they have it. This, however, is far from trivial.
Behind this somewhat obscure name hides a genetic disease that manifests itself in an alteration of the heart rhythm. The term “QT” also refers to the curve of the electrocardiogram, and more particularly to the interval between the beginning of the QRS wave and the end of the T wave. This interval corresponds to the time required for electrical signal to circulate in the ventricles of the heart, between the moment when it contracts and when it relaxes. Beyond 440 milliseconds, we speak of “long QT”. People who suffer from it are at significant risk of ventricular fibrillation manifesting in sudden death.
Generally discovered on the occasion of a malaise or syncope, the long QT syndrome is treated by the prescription of certain drugs of the beta-blocker type, which do not decrease the QT but lower the risk of complication. People who suffer from it must then avoid certain substances such as energy drinks but also grapefruit juice.
This is already on the list of substances to avoid when taking medication, as it increases its toxicity. A new study, published in Heart Rhythmthe official journal of the Heart Rhythm Society and the Cardiac Electrophysiology Society, confirms that it is all the more harmful since it has effects on the elongation of the QT interval.
Blockage of IKr channels
There are over 200 drugs that prolong the QT interval, which is the time it takes for the heart muscle to recharge between beats. The list includes not only antiarrhythmics, but also drugs without cardiac indications such as certain antibiotics, antihistamines and antipsychotics. These drugs work mainly by blocking a specific “IKr” potassium channel on the cell membrane of the myocardium (the heart muscle), thus prolonging the repolarization of the ventricles of the heart.
Certain foods may also have IKr channel blocking properties. This is the case with grapefruit juice. “Previous studies have shown that flavonoid compounds in grapefruit juice have IKr channel blocking properties. We therefore tested the possibility that grapefruit juice has QT-prolonging properties,” explains Sami Viskin, who led the work.
30 healthy volunteers and 10 patients with congenital long QT syndrome took part in an extensive four-day study. On days 1 and 3, participants received no study medication and underwent multiple electrocardiograms (ECGs) to check for spontaneous daily QT interval variability. On days two and four, healthy participants received either a 400 mg dose of moxifloxacin, an antibiotic with QT-prolonging properties, or grapefruit juice (two liters in three divided doses at hours apart) in random order. Patients with long QT syndrome received only grapefruit juice.
Better inform patients
The results confirmed that grapefruit juice prolongs the QT interval. In healthy volunteers, the net prolongation of the QT interval was small, but comparable to that caused by moxifloxacin. Grapefruit-induced QT prolongation was greater in women than in men and even greater in patients with congenital long QT syndrome.
For Dr. Viskin, these results confirm the harmful effects of grapefruit juice on the health of people suffering from long QT syndrome. This drink must therefore, according to him, be the subject of special warnings. He also recommends better informing patients that their consumption of grapefruit juice may pose a risk to their heart health.
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