The drug sildenafil, sold under the brand name Viagra, can strongly suppress abnormal heart rhythms, a new study has found.
In a study led by the University of Manchester, scientists found that Viagra was able to suppress a heart arrythmia in female sheep. The drug, which is used to treat sexual impotence, was able to supress the arrythmia, known as Torsades de Pointes, within 90 seconds by reducing the frequency of irregular heart rhythms caused by abnormal handling of calcium.
The research, which was funded by the British Heart Foundation, has been published in Circulation Research.
By working on isolated sheep heart muscle cells known as myocytes, the researchers were able to measure their calcium stores as well as their electrical properties. Although calcium is a key driver of the heart’s pumping action, its overload can cause arrythmias. In the study, the researchers found that Viagra was able to suppress the mechanism in the cell that causes calcium overload.
When a small amount of calcium enters a myocyte, it triggers the Sarcoplasmic Reticulum (SR)- a calcium store – to release a larger quantity of calcium. In heart disease cases, the SR can become overloaded with calcium which in turn makes the heart beat at the wrong time. The mechanism is part of an enzyme pathway inside the cell involving PDE5 and activates a protein called protein kinase G which impacts the arteries in the penis allowing blood to pump into it. A similar mechanism exists around the muscle cells of the heart but has never been studied until now.
Potential to treat other arrythmias
The research team believes that, as well reducing the risk of Torsades de Pointes, which can lead to sudden cardiac death, Viagra could also be used to treat other arrythmias.
Dr David Hutchings, a lecturer at The University of Manchester and the paper’s lead author, said: “Not only has this study demonstrated that Viagra has a powerful antiarrhythmic effect on living heart tissue, our cell studies have also uncovered the mechanism by which this happens.
“Though we studied the effect in sheep, we believe this discovery is likely to be relevant to humans. The human’s heart is a similar size to a sheep’s, as is its anatomy and associated electrical circuitry. So this discovery could one day unleash the potential for effective treatment on what can be a devastating problem.
“Clearly, anyone who has a cardiac arrythmia should not self-medicate and should consult their GP for advice on current treatment options.”
Principal Investigator Professor Andrew Trafford, from The University of Manchester, said: “This exciting study builds on our previous work funded by The British Heart Foundation around the effect of Viagra on the heart.
“In 2016, our study of patients with diabetes showed that incidental use of Viagra was linked with reduced heart attack risk and improved heart attack survival.
“In 2019, we found that Viagra can slow or even reverse the progression of heart failure in sheep and this work dramatically extends those important findings, providing another tool with which to beat heart disease.
“Much more work still needs to be done but we feel we are getting closer to an effective and powerful alternative to current treatments.”
Professor Metin Avkiran, Associate Medical Director at the British Heart Foundation, said: “A better understanding of how heart rhythm disturbances occur could pave the way for better preventions and treatments for them.
“This study suggests that the enzyme PDE5, which is suppressed by Viagra, may also play a key role in causing abnormal heart rhythms that arise from an overload of calcium in sheep heart cells. This could be important because the electrical behaviour in these cells is similar to that of human heart cells.
“More research is needed, however, before Viagra and similar drugs can be repurposed for treating abnormal heart rhythms in patients.”
