Atrial Fibrillation - Symptoms, Causes and Treatment
Atrial fibrillation is a very common cardiac arrhythmia that usually causes rapid, irregular heartbeat. Atrial fibrillation usually occurs in the elderly and with structural heart disease, such as valve disease, heart failure, or with cardiac electrical conduction disorders.
Let's do here a brief review of the anatomy of the heart so we can better understand what atrial fibrillation (AF) is.
Our heart has 4 chambers or cavities: left atrium, left ventricle, right atrium and right ventricle. The left side of the heart, composed of the atrium and the left ventricle, has no communication with the right side of the heart, composed of the atrium and the right ventricle.
The blood reaches the heart through the vena cava that flows into the right atrium (blue arrows). When the atrium is full, it contracts and pushes the blood into the right ventricle. When the ventricle becomes full, it also contracts, pumping blood toward the pulmonary arteries. The blood then passes through the lungs, receives oxygen and returns to the heart, reaching the left atrium (red arrows). Again, when the atrium is filled, it contracts and pushes the blood into the left ventricle. The left ventricle, when filled, pumps blood to the aortic artery, from where it will be distributed to the rest of the body. After running through the body, blood returns to the heart through the vena cava, restarting the cycle.
This whole process of cardiac contraction and blood pumping is finely synchronized, so that each event described occurs at a range of only hundredths of a second. Cardiac contraction is controlled by mild electrical impulses generated by a structure called the sinus node, located at the apex of the right atrium, composed of cells capable of generating electrical activity. If you want to better understand how cardiac electrical activity works, read: Electrocardiogram exam (ECG).
Cardiac arrhythmias are disorders that arise when there is a problem in the generation or distribution of these electrical impulses by the heart, causing the contraction of the cardiac cavities to lose this synchronism described just now.
Usually, the cardiac electrical impulses are generated solely by the sinus node, stimulating the contraction first of the right atrium, after the left atrium and, finally, the ventricles. A single electrical impulse takes 0.19 seconds to travel through the entire heart.
During normal cardiac activity, the sinus node fires electrical impulses rhythmically, with a minimum interval between each new pulse. It is no use for the heart to generate two or more simultaneous electrical impulses, for the heart muscle needs a few tenths of a second to recover and be able to contract again.
Atrial fibrillation is an arrhythmia caused by the onset of more than one point in the atria capable of triggering electrical impulses. When there are several electrical impulses being triggered simultaneously, in a chaotic way, the atrial muscles receive several orders of contraction at the same time, without time of rest, which ends up creating what we call atrial fibrillation.
In this arrhythmia, the atrium begins to make short, successive and ineffective contractions. Visually they seem to be shaking, as if they are carrying an electric shock or having a seizure. The normal atrium beats between 60 and 100 times per minute, which is the normal heart rate. In atrial fibrillation he can do up to 600 contractions (short and ineffective) per minute.
Fortunately, these chaotic electrical impulses can not reach the ventricles, as they must pass through a structure called the ventricular atrium node (AV node). This structure, located at the border between the atria and the ventricles, is able to filter out the hundreds of chaotic impulses that come in, allowing only 100 to 170 impulses per minute to pass (which causes a heart rate of 100 to 170 beats per minute ). The patient's heart is accelerated, but unlike what occurs in the atrium, there is a minimum interval between one impulse and the other so that the ventricles maintain their capacity for contraction intact.
As the atrial fibrillation does not contract properly, the passage of blood into the ventricle is impaired and does not occur linearly. The blood eventually creates a whirlwind within the atrium, causing some of it to be dammed, which favors the formation of clots (I will explain the consequences of these clots later on).
Age is one of the most important risk factors, with atrial fibrillation being a very common arrhythmia in the elderly. In more than 70% of AF cases the patient is over 65 years old. Only 0.1% of the population below the age of 55 years has atrial fibrillation.
Besides age, another important risk factor is the presence of heart disease; hypertension and coronary disease are the two most important. The long-term hypertensive patient usually has dilated atria, which favors the deregulation of the cardiac electrical system. Patients with coronary disease may present with ischemia of the cells that generate and conduct the electrical impulses, favoring the appearance of arrhythmias.
There are also risk factors for the development of atrial fibrillation:
If atrial fibrillation does not cause a major heart rate to accelerate, called tachycardia, it may even go unrecognized. In most cases, however, atrial fibrillation usually accompanies heart rates around 120-130 beats per minute, causing symptoms such as palpitations, chest discomfort, dizziness, tiredness, and/or shortness of breath.
A typical AF finding is an accelerated heart, over 100 beats per minute associated with a totally irregular beat rate.
If you experience palpitations or any of the symptoms of atrial fibrillation listed above, place your finger on your own wrist to assess your heart rate. The normal heart beats regularly, with equal time intervals between each beat. The heart rate is usually between 60 and 100 bpm.
A heart with regular rhythm beats with the following pattern:
Older patients, whose heart is already weakened, may not tolerate the tachycardia that atrial fibrillation produces, which in some cases exceeds 150 beats per minute, presenting a drop in blood pressure, lack of important air and/or intense malaise. If the patient already has ischemic heart disease, tachycardia may aggravate ischemia, causing angina pectoris or even myocardial infarction.
The major problem with atrial fibrillation is the increased risk of stroke. As the atrium does not contract properly, the blood can create a kind of swirling inside it, which favors the appearance of clots.
If one of these formed clots leaves the left atrium, it will be thrown directly to some point in the body (clots thrown into the circulation are called emboli).
If this plunger from the heart rises toward the brain, as soon as it reaches a finer artery, it will be impacted, immediately blocking the arrival of blood through this artery, thus causing ischemia in part of the brain (see the illustation beside).
The plunger can also travel to other parts of the body and may cause thrombosis and ischemia in the eyes, kidneys, intestines, spine or even toes if the plunger is too small and travels to the extremities of the body without impacting before.
Atrial fibrillation is classified in 4 ways: newly diagnosed, paroxysmal, persistent or permanent.
A. Newly diagnosed atrial fibrillation: every AF when it is first detected is classified as newly diagnosed. In some situations, based on the symptoms of palpitation, it is possible to determine the exact moment of its onset. However, there are cases of asymptomatic atrial fibrillation, causing many patients to have the arrhythmia and do not know it. These cases are usually discovered accidentally during a routine medical examination.
B. Paroxysmal atrial fibrillation: they are patients with recurrent AF episodes of short duration. Usually the patient presents at least 2 episodes per week, lasting less than 24 hours and spontaneous resolution of the condition.
C. Persistent atrial fibrillation: these are the cases of AF that do not disappear spontaneously and need to be treated with antiarrhythmic drugs or electrical cardioversion to be reversed (explained below in the treatment part).
D. Permanent atrial fibrillation: these are the cases of AF that last more than a year and do not disappear spontaneously or with medical treatment.
The diagnosis of atrial fibrillation is easily made through the electrocardiogram. In cases of paroxysmal atrial fibrillation, an exam called Holter may be needed. In this examination, the patient has an electrocardiogram device attached to his body for 24 to 48 hours, and it is possible to detect the onset of short periods of AF within this time interval.
The echocardiogram (a kind of ultrasound of the heart) is also capable of detecting atrial fibrillation. Its great advantage is to also be able to evaluate the size of the ventricles and the atria. Patients with a very dilated heart usually do not respond well to treatments that aim to reverse AF.
The treatment of atrial fibrillation may have 3 lines of action:
1. Reversing fibrillation
2. Do not reverse fibrillation but control heart rate
3. Prevent the formation of clots within the atria
Cardioversion
Cardioversion is the term used to reverse atrial fibrillation. Electric cardioversion is performed with a device that causes shock, similar to what is done in some cases of cardiac arrest. Electrical cardioversion is usually only done in more severe cases, when the patient is suffering from hypotension or risk of acute myocardial infarction. Pharmacological cardioversion is the one that is obtained with the use of venous antiarrhythmic drugs.
Cardioversion, whether electrical or pharmacological, is indicated in cases of AF of recent onset, when the risk of clots formed in the left atrium is low. However, if the patient is elderly and already has a very large or diseased heart, the success rate of cardioversion is very low, and its performance is not indicated. Cardioversion works best in patients not so old and with a healthy heart.
The major risk of cardioversion is the embolization of a clot to the brain at a time when the atrium recovers normally. In cases of AF more than 24 hours, the patient should be treated with anticoagulants for at least 3 weeks prior to cardioversion to minimize the risk of embolization. An alternative is to perform an echocardiogram through the esophagus to look for clots in the left atrium. If there are no visible clots, cardioversion can be done even if the patient has not taken anticoagulants for at least 3 weeks.
Heart rate control
In cases of long-term atrial fibrillation or in elderly patients with an already very diseased heart, cardioversion is usually not used because its success rate is low. In these cases, the treatment aims only to control the heart rate. As most AF symptoms are due to tachycardia, when we maintain the patient with frequencies below 100 beats per minute, his atrial fibrillation becomes asymptomatic.
Heart rate control is achieved with medications. The most commonly used are amiodarone, propafenone, digoxin, diltiazem, verapamil or metoprolol.
Anticoagulation
All patients with atrial fibrillation should be medicated with anticoagulant drugs to prevent the formation of clots in the left atrium. The most commonly used medication is warfarin. The major problem with warfarin is the risk of bleeding and the need to get blood tests often to control your blood level.
Recently launched three new drugs that are good alternatives to warfarin because they do not need control with blood tests. They are: Dabigatrana, Apixabana and Rivaroxabana.
In patients who are very old or have difficulty controlling their own medicines, the use of anticoagulants can be dangerous because the risk of bleeding is high. In these cases, the doctor may choose to prescribe only drugs that inhibit platelets, such as aspirin. The prevention of clots is not as effective, but the risk of bleeding is much lower.
