Dr. José L. Merino is one of the Spanish cardiologists with the most national experience in cardiac arrhythmias and with prestige and international recognition in catheter ablation of complex forms, such as atrial fibrillation, atrial flutter and ventricular tachycardia.
In this article he discusses atrial fibrillation (AF), a form of tachycardia (i.e. an arrhythmia due to excess heartbeats). Exactly how it occurs is not known, but the result is that the upper part of the heart, the atria, has a rapid and chaotic rhythm.
Explanation of atrial fibrillation
To understand it, we must start from what is the normal rhythm of the heart, known as sinus rhythm. In the attached animation it is represented and can be seen how the heart is divided into 4 chambers, 2 atria and 2 ventricles. The blood arrives through the veins to the atria (AD and AI) and from there passes to the ventricles (VD and VI) through the cardiac valves.
The latter are the most important in cardiac contraction and the ones that pump the blood and expel it through large arteries, such as the aorta (Ao), which is not well represented in this diagram. This contraction of the cardiac muscle is produced by electrical currents that arise from a point. It is as if an electric spark (represented by the little circle with waves in the animation) were to jump. From this “spark” electric waves are formed, similar to those produced when a stone is thrown into a pond, but in this case they are electric waves represented in the diagram by green arrows and which, as they advance, cause the cardiac muscle to contract.
Upon reaching the junction of the atria and ventricles, these waves encounter a kind of insulator, so that they can only reach the lower part of the ventricles through a kind of cable or filter (in the NAV scheme) and, from there, again the electrical fronts are transmitted through the ventricles causing them to contract.
In AF, a kind of electrical chaos is formed in the atria (represented as AD in the animation) so that there are many erratic waves that are perpetuated without ever ending and cause these cavities to accelerate at more than 300 beats per minute, so fast that they do not have time to fill or empty completely. Fortunately, the filter/isolator system prevents the ventricles from reaching such rapid rates.
Is it common and can it be hereditary?
AF is a very common arrhythmia, in fact, it is the most common sustained arrhythmia. In the general population, two out of every 100 people have it and even, in recent studies in our country, 4 out of every 100 people over 40 years of age have it. That is to say, in Spain around one million people suffer from it and one in four men and one in five women will have it during their lifetime.
Although a greater predisposition to suffer from it has been described when there is a family history, this risk is only doubled and does not necessarily mean that one will have it. On the other hand, some rare hereditary forms have been described that manifest themselves in patients who present it at an early age.
What are the causes?
The causes of AF are not known and are currently a field of research. What is known are the predisposing factors. The two most important are age and arterial hypertension (AHT). AF is an arrhythmia that frequently manifests with age, being present in up to one in 10 people over 80 years of age. Arterial hypertension is one of the major risk factors and in fact 70% of patients with AF are hypertensive. Recently, obesity and lack of physical exercise have been found to be risk factors for arrhythmia and correction of these factors improves response to treatment.
How is it recognized?
The diagnosis of AF is relatively simple and is made with a simple electrocardiogram (ECG). Patients may suspect it because the pulse is usually arrhythmic, i.e. it does not follow a regular rhythmic cadence but is totally uncoordinated but not necessarily fast. For this reason it is recommended that patients adopt the habit of taking their pulse when they get up in the morning, for example.
What symptoms can it generate?
The typical symptom of AF is palpitations: noticing the heart going fast and/or arrhythmic. This is because, although not all the waves pass from the atria to the ventricles, they tend to pass many and irregularly. Other patients, especially when it becomes chronic, may notice tiredness and shortness of breath. In the strangest cases, dizziness and chest pain may occur.
Is it dangerous and what are the consequences?
AF is not usually dangerous in the short term. That is to say, in most patients it can produce the symptoms previously mentioned, but it does not usually have dangerous consequences in the short term. However, in the medium and long term it can be dangerous because, on the one hand, it causes the ventricles to become damaged and tired, leading to heart failure, and, on the other hand, it predisposes to the formation of intracardiac clots which, if detached, can end up clogging an artery in the brain (cerebral embolism). Because of these effects, it is known that this arrhythmia doubles the risk of death in those who suffer from it.
What treatments are available?
The treatment of this arrhythmia is basically aimed at 3 aspects. The first and most important is to prevent embolisms with anticoagulants. The second is to prevent the ventricles from going too fast when the arrhythmia occurs and to prevent them from tiring, and for this purpose drugs are used that increase the filtering capacity of the “cable” (of the AV node). Finally, the best option is to avoid AF episodes. Antiarrhythmic drugs can be tried. Moreover, these drugs do not “cure” the arrhythmia as antibiotics do with infections, but must be maintained chronically.
What is cardioversion?
It is the administration of an electric shock which, being painful, is performed with the patient sedated. It is not a curative technique but rather seeks to “reset” the heart to bring it back to the starting situation. That is to say, it does not cure the problem or what has led to it, and it can reappear in the evolution, although at least for a time a normal cardiac rhythm is recovered.
What is ablation and can it cure the problem?
Ablation is a catheterization technique, that is to say, it consists of introducing thin catheters or tubes through a vein in the leg and taking them to the heart. Once there, the cardiac electrical currents are studied and an attempt is made to determine what is causing the arrhythmia. In a second step, one of these catheters is used to carry it to the points in the atria thought to be related to AF and, by heating the tip of the catheter, these points are cauterized and removed.