Credit: Michelle Banks via Flickr
It's not uncommon to see TV commercials or magazine ads promoting medications to treat atrial fibrillation. It is a major public health concern affecting millions of people globally. But, surprisingly, now there's a potential treatment taking shape that utilizes one of the world's most potent and lethal toxins.
Atrial fibrillation (AF or A-fib) is the most common heart arrhythmia. AF Patients have an increased risk of experiencing heart failure, stroke and even death. Both the incidence and prevalence of atrial fibrillation are on the rise, placing a major burden on the healthcare system.
Botulism toxin -- Botox -- has many clinical uses (treatment of spasms, dystonias such as torticollis, overactive bladders, excessive sweating, just to name a few) but it is most popularly known as a cosmetic agent to smooth out wrinkles. But a new study in the American Heart Association Journals describes how Botox can be used to block the development of this irregular heart rhythm.
The team of scientists injected the toxin into the areas of the heart where the nodes that regulate heart rate are located. These nodes (known as the "SA" or "AV" nodes) are affected by the vagus nerve. The vagus nerve is responsible for mediating the lowering of the heart rate. Canine models are chosen for this study because their hearts share anatomic similarities with human hearts, thus the effects observed in the dog model can reliably predict those in humans.
Botulinum toxin, comes from the bacteria Clostridium botulinum. The toxin effectively paralyzes skeletal muscles by blocking neurotransmission of a chemical needed for movement. Similarly, it will block that same chemical from being released by the vagus nerve, thus blocking its action on the heart.
Globally, AF has been estimated to affect 33.5 million people, with about five million new cases occurring each year. Between 1996 and 1997 in the U.S. alone, roughly 2.3 million adults had AF, and this total is estimated to increase to 5.6 million cases by 2050.
The results of the study showed the ability to suppress the development of AF, most significantly at one week after injection of the toxin at the level of the vagus nerve. But the drug lost effectiveness in subsequent weeks.
The treatment is still preliminary, and in particular the lack of long-term benefits are disheartening. However, Botox for AF may have a future in postoperative cardiac patients.
AF occurs in up to 50 percent of cardiac surgery patients, and it's the most common postoperative arrhythmic complication. AF occurs within one week of surgery in this particular population, therefore, having an effective strategy for a nonpermanent, nondestructive, neurochemical block would be valuable.
The risk of developing AF depends on age and whether one has an underlying heart disease. In developed countries, hypertension and coronary heart disease are the most common underlying chronic conditions associated with AF. In developing countries, rheumatic heart disease is also an associated risk factor.
We have a ways to go before we can introduce this intervention in the human population. However, given the sheer enormity of AF disease burden, the prospects of this study are an exciting foray into future treatments.
