When the heart gets out of rhythm, it often manifests itself as an uncomfortable heart racing or palpitations. Such arrhythmias are among the most common complications in adults with congenital heart defects (ACHD). They can be particularly dangerous for them and therefore belong in the hands of experienced specialists. Countermeasures can be taken either by catheter ablation or by medication. With the latter, however, caution is advised, as a recent study at the Competence Network for Congenital Heart Defects shows.

Discovered By Chance: Active Substance Against Cardiac Arrhythmias

In Germany, for example, they are called Amiogamma®, Amiohexal® or Cordarex®. These are drugs to treat cardiac arrhythmias that are based on the active ingredient amiodarone. This active substance was originally developed for the treatment of angina pectoris until it was discovered by chance that it has an inhibitory effect on ventricular and supraventricular arrhythmias. Since then, it has been popularly prescribed for cardiac arrhythmias originating in the myocardial tissue above the ventricles. Especially in patients with congenital heart defects, amiodarone is often the drug of choice because other antiarrhythmic drugs are not an option or simply do not work. However, the iodine-containing drug can cause severe side effects, including impairment of the thyreoid function.

Thyroid Dysfunction Is a Risk

It is known from studies that thyroid dysfunction in patients with congenital heart defects is one of the risk factors associated with increased mortality. How often does this amiodarone side effect occur in patients with congenital heart defects? What are the exact risk factors? And what are the therapeutic consequences of amiodarone-induced thyroid dysfunction? These questions were addressed in one of the most comprehensive studies to date on this side effect of the drug.

National Study Suggests Alternative Forms of Treatment

Based on anonymized data from Barmer Health Insurance, the researchers were able to follow up about 50,000 patients aged 16 and older who had been treated with amiodarone at least once between 2005 and 2018, including 886 patients with congenital heart defects. Thirty-eight percent of those observed without congenital heart defects and 35 percent of those observed with congenital heart defects developed thyroid dysfunction over a 10-year period.

"The incidence of this side effect is basically quite high in both groups. It increases with the duration and frequency of taking the drug. However, younger women in particular with severe congenital heart defects tend to develop thyroid dysfunction under amiodarone. This suggests that we should take a closer look at this patient group and, if possible, preferring catheter ablation over drug treatment in accordance with the guideline recommendations," said lead author Alicia Jeanette Fischer, specialist for Internal Medicine and Cardiology at the ACHD Center of Münster University Hospital, summarizing the findings.

Further Risk Factors Identified

In addition to age and gender, scientists were able to identify further risk factors. Patients with a pacemaker were found to be more susceptible to thyroid dysfunction under amiodarone, as were patients after implantation of a cardioverter defibrillator. Chronic kidney disease as well as alcohol consumption and smoking also favored the development of this side effect.

Joyful Alternatives to Alcohol and Tobacco Consumption

According to Alicia Jeanette Fischer, it is generally a gain in quality of life to exchange the consumption of alcohol and tobacco, including the smoking of e-cigarettes, for joyful activities such as running, walking or hiking, yoga, tai chi, dancing or meditation and a balanced diet rich in vitamins and fiber and low in meat, sugar and salt, as well as water as a thirst quencher, "especially when the body already has to perform amazing things due to a congenital heart defect. We have actually known for thousands of years that we strengthen our bodies and our psyches through exercise, sufficient sleep and good food, and thus noticeably increase our general well-being."

The doctor is well aware of how difficult it can be to completely give up the after-work-beer, wine or cigarettes. "The withdrawal works best when we evaluate it not as a renunciation, but as a reward for our body. We breathe much better, sleep better, can move better and concentrate better."

Restrained Medication Prescription and Continuously Monitored Use

Of concern to the researchers is that catheter ablation was used in only 42 percent of ACHD patients and in 34 percent of all patients followed up. "We were surprised by the relatively frequent administration of amiodarone, especially since catheter ablation is recommended in current guidelines as the treatment of first choice for many arrhythmias," said study leader Professor Gerhard-Paul Diller, ACHD specialist at Münster University Hospital.

Moreover, despite thyroid dysfunction, amiodarone administration was continued in almost half of the patients without congenital heart defects (47 percent) and still in more than a third (38 percent) of the adults with a congenital heart defect. 3.5 percent of ACHD patients underwent thyroid surgery or radiation. For all other patients, the figure was 2.3 percent.

"We strongly advise that amiodarone be used only when no suitable alternatives with a more favorable side effect profile are available. Patients requiring amiodarone should be thoroughly examined for any existing thyroid disease before the first prescription and continuously monitored for thyroid dysfunction," emphasizes Professor Gerhard-Paul Diller. This is even more true for people with specific risk factors, such as younger female patients and patients with complex congenital heart defects, as they may be more susceptible to developing complications, he adds.

Discontinuation of Amiodarone Versus Thyroid Surgery

In both hypothyroidism and hyperthyroidism, discontinuation of amiodarone may lead to recovery of its function. However, because the benefit of discontinuation is time-delayed, the likely recovery of thyroid function must be carefully weighed against the need for treatment with amiodarone in the absence of alternative management options for cardiac arrhythmias due to a congenital heart defect.

The authors of the study were therefore surprised to learn that radiation therapy or thyroid surgery is performed less frequently in adults with congenital heart defects than in all other patients. From their perspective, this is concerning because surgery and radiation are the most effective treatments for hyperthyroidism in many cases.