Ivabradine for Inappropriate Sinus Tachycardia

Inappropriate sinus tachycardia (IST) is a condition characterized by an abnormally rapid heart rate (tachycardia), both at rest and during exertion. It usually affects younger people who are otherwise completely healthy.

Those who suffer from IST commonly experience severe palpitations as well as exercise intolerance and fatigue. The condition can be quite disabling, and unfortunately, treating IST effectively is often challenging.

Ivabradine is a relatively new drug marketed for the treatment of angina and heart failure. In recent years ivabradine has shown significant promise for the treatment of IST.

Reports indicate that it might also be effective for other dysautonomia syndromes in which tachycardia is often a prominent feature.

How Does Ivabradine Work?

Ivabradine was originally developed for treating angina and was approved for use in much of the world in 2005. Under the brand name Corlanor, ivabradine was approved in the U.S. in April 2015 for the treatment of heart failure, but not for IST.

If you have IST (or one of the other dysautonomias that may respond to this drug) and your doctor believes that ivabradine may be beneficial to you, they are now able to prescribe it.

However, since ivabradine is only indicated for heart failure, your doctor must be willing to prescribe it for "off-label" use. In any case, ivabradine is now a realistic option for those who have IST.

Ivabradine works by blocking the funny channel (IF), a channel in cell membranes that allows sodium and potassium to enter cells. The IF channel (referred to as "funny" because it behaves differently than most other channels), plays a major role in firing the sinus node, which regulates the normal heart rhythm.

By blocking the IF channel, ivabradine slows the rate of firing of the sinus node, and thus slows the heart rate.

This mechanism of slowing the sinus heart rate is fundamentally different from the mechanisms employed by beta-blockers and calcium channel blockers, so ivabradine often produces slowing of the heart rate even when these other drugs fail to do so.

Ivabradine In IST

Several small reports—often describing one or two patients—began appearing soon after the drug came into clinical use, suggesting that ivabradine might be useful in treating patients with IST.

Then, in 2012, a well-designed randomized, placebo-controlled clinical trial was reported in Italy. It concluded that ivabradine may indeed be uniquely effective for this condition.

IST patients randomized to ivabradine showed about a 70% reduction in symptoms, and approximately 50% of treated patients reported immediate and complete resolution of symptoms.

Side effects were minimal. Compared to what is typically seen with other medical treatments used for IST, such a result is indeed striking.

In 2013, a non-randomized trial with ivabradine in 24 patients with IST showed similar favorable outcomes. In this trial, however, the drug was stopped in 10 patients after one year to see what would happen (the other patients refused to stop taking the drug), and eight of these patients had no recurrence of IST.

Ivabradine for POTS and Vasovagal Syncope

Postural orthostatic tachycardia syndrome (POTS) and vasovagal syncope are two other dysautonomia syndromes in which sinus node tachycardia often plays a prominent role in producing symptoms. So it is not surprising that doctors would choose to try ivabradine in these conditions.

There is limited data on the use of ivabradine for POTS, but doctors around the world have used the drug in selected individuals with this condition. The data that does exist suggests that, at least in some people, controlling the tachycardia with ivabradine can reduce or eliminate the other symptoms associated with POTS.

While vasovagal syncope is associated with a precipitous drop in blood pressure and (usually) in heart rate, it is well known that, prior to the loss of consciousness (or during the “warning symptoms” people often experience with this condition), an abnormally rapid heart rate is often present.

In a pilot study of 25 patients with vasovagal syncope who demonstrated such a tachycardia just prior to passing out, over 70% had favorable results with ivabradine—either a significant reduction or elimination of symptoms.

All in all, ivabradine shows real promise for all the dysautonomias in which sinus tachycardia is a major feature.

Side Effects

The only prominent side effect reported with ivabradine, seen in around 15% of patients, is a visual condition called the luminous phenomenon. This is described as experiencing an abnormal “brightness” in the visual fields without any change in visual acuity. It is thought to result from blocking a channel in retinal cells that is similar to the IF channel in the heart.

Fortunately, this side effect is usually mild and most often resolves on its own.

One report suggests that patients on this drug may have an increased risk of atrial fibrillation. Other less common side effects include headache and dizziness. Overall the drug is reportedly tolerated quite well.

A Word From Verywell

Inappropriate sinus tachycardia is a source of anxiety for many people, particularly since it is difficult to treat and may not be possible to prevent. While ivabradine is known to be effective in reducing the risk of heart failure and angina, it is not approved as a treatment for IST. That said, studies demonstrating ivabradine's ability to regulate heart rhythm in people with IST are encouraging.

Not all doctors are willing to prescribe medication for off-label use. However, if you are worried about your IST or the condition is interfering with your daily life, it's worth asking your doctor about ivabradine as a possible treatment option.