Bradiarhythmias. 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 range of normal heart rate can vary, so that larger hearts can work at frequencies of 50-90 bpm and be normal.
Summary
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- 1 How is it produced?
- 2 Symptoms
- 3 Diagnosis
- 4 Treatment
- 5 Preventive measures
- 6 Source
How is it produced?
The electrical impulse that allows the heart’s muscle fibers to contract and relax and pump bloodthrough its cavities it is transmitted through nerve fibers inserted into the heart muscle. The electric current originates from a structure called the sinus node that is located on 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 the 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, 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 lower than normal heart rate per se 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 the electrical conduction.
The dysfunction caused by bradyarrhythmia can also be found in the atrioventricular node, in the bundle of His, in its branches or in the Purkinje network. The more distal the location of the conduction failure, the worse the prognosis and the fewer treatment options. Atrioventricular node blockage may also be due to ischemiaafter a heart attack, to 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 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 ineffectiveness of pumping the blood, which occurs at a lower rate than normal. Patients usually report dizziness, syncope pictures (sometimes without passing out), tiredness and muscle weakness.
Patients do not usually explain chest pain nor are they aware of the alteration of the heart rhythm, unlike the palpitations that 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 acceleration of the heart rate. In cases of severe bradyarrhythmia, cardiac arrest may occur.
Diagnosis
Bradyarrhythmia should be ruled out in all patients who present symptoms compatible with it such as recurrent syncopes, dizziness, severe asthenia and the absence of increased heart rate due to stimuli that cause physiological tachycardia.
The main and most immediate diagnostic tool will be the electrocardiogram, which will allow us to determine the heart rate and assess where the heart rhythm disturbance is, since depending on the location of the failure in the conduction system, the electrocardiogram will be different. For the study of a bradyarrhythmia, a Holter is usually performed, which consists of recording the heart rate for 24 hours, which allows evaluating alterations at times when the patient does not present any symptoms. It is especially useful for determining disturbances of the sinus node or conduction between it and the atrioventricular node.
Other diagnostic tests that may be requested are an electrophysiological study, a test that allows the entire electrical conduction network of the heart to be traced and, through the use of drugs, to assess its response and determine where the cause of the bradyarrhythmia can be found.
The echocardiogram allows us to assess defects in the contractility of the atria and ventricles and determine ischemic lesions that can explain the origin of the conduction alteration. Likewise, individual photon emission computed tomography (SPECT) also allows us 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 alteration of the sinus node or the transmission of the impulse from it to the atrioventricular node, it will not be treated unless the patient presents symptoms. In case of presenting them, the best option is to implant a permanent pacemaker.
If the bradycardia is due to a malfunction of the atrioventricular node or its ramifications, a pacemaker will be implanted, which may be transient, if it is the cause, such as an infection or a tumor that can be operated on and eradicated. In the case of a permanent cause, as most of them are, or of high-grade heart rhythm blocks, a permanent pacemaker will be chosen.
Self-implantable defibrillators (ICDs) are devices that are implanted at the level of the left pectoral and are connected to the heart by electrodes. They monitor the heart rate and if they detect an alteration of the heart rate and heart rate, they try to revert 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 acute bradycardia, one can try to reverse the rhythm using different heart rate stimulating drugs.
Preventive measures
Efforts should be made to lead a healthy life that reduces cardiovascular risk factors. A balanced low-fat diet, moderate and regular sports, and avoiding tobacco and alcohol can help keep your heart in shape