QT interval is the time duration between the start of the Q wave up to the end of the T wave in an ECG. The heart follows an electrical cycle. An ECG is the graphical representation of this electrical cycle on a paper. The electrical conduction of the heart is responsible for the contraction of the heart muscles. Because of this mechanism, the blood is pumped through the body in a carefully programmed way. In this process, the right and the left atrium contract first, and then the right and left ventricles contract. This systematic contraction and relaxation is very carefully designed to facilitate the pumping of the blood through the body.
There are many factors which can affect this systematic mechanism of action. Certain heart disorders, other medical conditions, even if not related directly to the heart, many lifestyle patterns and certain medications can disturb this carefully designed system, which can prove to be quite fatal at times.
Before commenting upon whether amitriptyline is responsible for the prolongation of the QT interval, it is first best to know the mechanism of action of this particular drug.
Amitriptyline is a prescription drug. It is a tricyclic antidepressant and is generally used to treat anxiety and depression related medical issues. Though the exact mechanism of action of amitriptyline in humans is not clearly known, it has been established that it does not cause any stimulation to the central nervous system. Some of the side effects of amitriptyline are blurred vision, constipation and dry mouth.
There is some speculation and confirmation to an extent about the link between some tricyclic anti-depressant drugs and the prolonged QT interval, torsades de pointes, ventricular fibrillation and sudden cardiac death. Amitriptyline is also a subject for this speculation. This is speculated to be related to the metabolism of a particular drug. It was also found that in patients of these conditions, there were also some other risk factors like a family history of congenital long QT syndrome, metabolic diseases, age and sex of the person, and simultaneous inclusion of other drugs which are responsible for prolonged QT interval.
Does Amitriptyline Prolong QT Interval?
As far as amitriptyline is concerned, yes it can be considered as a potential risk factor for long QT syndrome, especially if it is combined with other risky drugs. Hence, this drug should be carefully prescribed, as it is one of the most important drugs in the medical index and cannot be withdrawn totally.
Many drugs that are otherwise commonly used, may have a potential of increasing the QT interval, and especially, so if they are combined and given with some other drugs which affect their metabolism. Therefore, utmost care is to be taken while administering these drugs.
Some people are more prone to be suffering from LQTS (long QT syndrome), than the others, though the exact reason for this is not yet known. This may be because of some congenital factors, mutations which must have taken place in some individuals and not in others; or it could be acquired, such as in conditions like hypokalemia, hypomagnesemia, cardiac failure, kidney failure, etc.
Long QT interval is associated with serious ventricular tachycardia, as seen in torsades de pointes, a fatal condition, which may degenerate further to ventricular fibrillation, and be responsible for a sudden death of the person, within seconds!
It is seen that the prolongation of the QT interval happens mostly because the potassium channels are blocked, which affect the repolarization in the heart’s conduction system. This effect is caused many times by the anti-arrhythmic drugs. Sometimes, the drugs such as anti-histamines, anti-depressants, anti-psychotic, antifungal and antibiotics may also be responsible for this.
Hence, the merits and demerits of prescribing any drugs together should be carefully thought of, before administration of any such drugs. Any drug, which affects the metabolism of another particular drug, can be a risk factor for causing a prolonged QT interval.
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