Atrial fibrillation is a heart disorder that causes the upper chambers of the heart to spasm instead of beating regularly. While that sounds dangerous, the lack of a regular heartbeat itself isn’t dangerous. Instead, a-fib causes lots of indirect problems that can be debilitating or fatal. We’re making progress in understanding the disease, as evidenced by two new papers that identify a total of 18 genes that predispose people to a-fib.
That should be exciting news. And it should be especially exciting to me, since I could have easily contributed to that study—as one of its subjects. I have a-fib, which I seem to have inherited from my mother.
Getting a better understanding of a disease can open all sorts of possibilities for better treatments, even ones tailored to your own particular genetics. But that’s not really the case with a-fib, and it provides a great example of how science can sometimes run up against limits even as it successfully increases our knowledge.
Feel the fib (or not)
Your heart has four chambers, two smaller ones on top called atria, and two much larger ones called ventricles. The rhythmic beat of your heart is the product of the regular contractions of these sets of chambers, first the atria, and then the ventricles. These contractions are organized by the unique properties of the heart muscle cells. These cells are driven to contract by a small electrical jolt delivered by a neighboring cell. In addition to contracting, this jolt causes these cells to release ions from storage areas, creating a small electrical jolt that they forward to their neighbors.
Some of their neighbors have already contracted, and so can’t respond to this electrical signal immediately. The rest contract and forward it on further. This creates a wave of contractions that can only travel in one direction: away from the source of the signal at the top of the atria (or top of the ventricles), towards cells that haven’t yet been triggered to contract. This organized wave of contraction, combined with a system of valves, drives the flow of blood in one direction.
In a-fib, all of this goes wrong. Multiple signals start, and take confused routes through the heart. Rather than a directional wave of contraction, the atria twitch and spasm. Rather than being driven in to the ventricles, the blood gets pulled in irregularly as they expand.
This might sound catastrophic, but the main force driving your blood through your body is the contraction of the larger ventricles. Some people remain completely unaware that they’ve developed a-fib until it’s picked up during routine screening. Others, however, experience a variety of symptoms: pounding or irregular heart beats, changes in blood pressure, light headedness, and more. (My a-fib announced itself by a racing, pounding heartbeat that woke me from sleep at two in the morning.)
But none of those symptoms makes a-fib a serious health threat. Instead, the problems are invisible and insidious….