Bradyarrhythmias

The heart beats at a normal rate at a rate of between 60 and 100 beats per minute (bpm). Depending on the size of the heart, the normal range of the heart rate can vary, so that larger hearts can operate at rates of 50-90 bpm and be normal.

When a drop in heart rate below 50-60 bpm it is said that the person suffers from bradyarrhythmia or bradycardia, that is, a rhythm slower than adequate to allow the pumping of the blood to ensure the correct perfusion and oxygenation of the body's tissues.

How is it produced?

The electrical impulse that allows the heart's muscle fibers to contract and relax and pump blood through their chambers is transmitted through a few nerve fibers inserted into the heart muscle. The electrical current originates in a structure called the sinus node that is located in the upper wall of the right atrium.

From there the electrical impulse is transmitted to the atrioventricular node, located between the two ventricles, which modulates the impulse received. The electric current is transmitted from it through the bundle of His, which in turn is divided into two branches, left and right, and from them arise the rest of fibers that form a network called Purkinje and through which the impulse to the rest of the contractile myocardial fibers.

Depending on the place where the alteration is found, the bradyarrhythmia can be of different types, which implies different symptoms, alterations in complementary tests, treatments and prognoses.

The abnormal function of the sinus node can respond to different causes, such as ischemia of the heart tissue secondary to a heart attack, systemic diseases or diseases that infiltrate the heart tissue such as amyloidosis. However, it must be said that most of the time the cause is unknown.

The sinus node may determine a heart rate that is lower than normal, or there may be a conduction block between it and the atrioventricular node. Said blockage can be of different degrees depending on the severity of the interruption of electrical conduction.

The dysfunction that causes bradyarrhythmia can also be found in the atrioventricular node, in the bundle of His, in its branches or in the al purkinje network. The more distal the location of the conduction failure is, the worse the prognosis and the fewer the treatment options.

Atrioventricular node block can also be due to ischemia after a heart attack, certain infections, drugs such as digoxin or beta blockers, heart tumors or diseases that infiltrate the myocardium. There are congenital alterations of this structure, but the most frequent cause in adults is the degeneration of the nodule or of the electrical impulse transmission network.

There are different degrees of atrioventricular block with different repercussions on the electrocardiogram. The most extreme form is atrioventricular dissociation, in which the atria and ventricles are governed by two different pacemakers.

Symptoms

The symptoms that a bradyarrhythmia produces are secondary to the lack of efficiency of the blood pump, which occurs at a lower than normal rate. Patients often report dizziness (sometimes without fainting), tiredness and muscle weakness.

Patients do not usually explain chest pain or are aware of the heart rhythm disturbance, unlike the palpitations they perceive in the case of tachyarrhythmias. However, when faced with stimuli that should accelerate the heart rate, such as physical activity or fever, patients note the absence of the acceleration of the heart rate.

In cases of severe bradyarrhythmia, cardiac arrest can occur.

Diagnosis

Bradyarrhythmia should be ruled out in all patients with symptoms compatible with it, such as recurrent syncope, dizziness, severe asthenia, and the absence of an increased heart rate in the face of stimuli that cause physiological tachycardia.

The main and most immediate diagnostic tool will be the one, which will allow determining the heart rhythm and assessing where the heart rhythm alteration is, because depending on the location of the failure in the conduction system, the tracing of the electrocardiogram will be different.

For the study of a bradyarrhythmia it is usually perform a Holter, which consists of recording the heart rhythm for 24 hours, which makes it possible to assess alterations at times when the patient does not present any symptoms. It is especially useful in determining abnormalities in the sinus node or in the conduction between it and the atrioventricular node.

Other diagnostic tests that may be ordered include a electrophysiological study, a test that allows a tracing of the entire electrical conduction network of the heart and, through the use of drugs, assess its response and determine where the cause of the bradyarrhythmia can be found.

The echocardiogram allows to assess defects in the contractility of the atria and ventricles and to determine ischemic lesions that can explain the origin of the conduction alteration. Likewise, single photon emission computed tomography (SPECT) also makes it possible to assess the contraction capacity of the heart muscle.

Treatment

Treatment is based on restoring normal heart rhythm whenever necessary and possible.

When bradyarrhythmia is identified due to an abnormal sinus node or its transmission of impulse to the atrioventricular node, it will not be treated unless the patient is symptomatic. In case of presenting them, the best option is to implant a permanent pacemaker.

If bradycardia is due to a malfunction of the atrioventricular node or its ramifications, a pacemaker will be implanted, which may be temporary, if the cause is, such as an infection or a tumor that can be intervened and eradicated. In the case of a permanent cause, as is usually the case, or high-grade heart rate blocks, a permanent pacemaker will be chosen.

The self-implantable defibrillators (ICD) They are devices that are implanted at the level of the left chest and that are connected to the heart by means of electrodes. They monitor the heart rhythm and if they detect an alteration in it and the heart rate, they try to reverse it to a normal rhythm by means of an electric shock. ICDs are indicated in patients with severe bradyarrhythmias at risk of cardiac arrest.

In the case of acute bradycardia, an attempt can be made to reverse the rhythm using different heart rate stimulating drugs.

Precautionary measures

You should try to lead a healthy life that decrease cardiovascular risk factors. A balanced low-fat diet, moderate and regular sports, and avoiding tobacco and alcohol can help keep your heart in shape.