Introduction
AV block or atrioventricular block is a disturbance in the normal electrical conduction of the heart, specifically between the atrium and ventricle. A delay or staggered conduction through the atrioventricular node may lead to calcification or fibrosis and can thus cause a complete atrioventricular block.
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The heart is divided into four main divisions. The upper division has two parts, called the right and left atrium. The lower division has two parts as well, called the right and left ventricles.
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Atrioventricular conduction is the normal electrical impulse conduction between the atrium and the ventricles.
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The AV node, or the atrioventricular node, is a tiny structure located in the heart. The chief function of this atrioventricular node is to control the flow of the heart’s electrical signals that are getting transmitted from the atrium to the ventricles.
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On the other hand, this HPS or the His-Purkinje System has the duty to rapidly conduct the electrical signals to the ventricles.
When the atrioventricular node or, alternately, the His-Purkinje System does not work efficiently due to some obstruction, it leads to a condition called AV block or atrioventricular block.
What Causes an Atrioventricular Block?
There are multiple reasons that may lead to an atrioventricular block. Most of them are due to an underlying cardiovascular condition that has been ignored or not diagnosed correctly, leading to the formation of the atrioventricular coalition over time. Following are the conditions that lead to an atrioventricular block.
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Degenerative changes in the heart’s structure.
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Infection of the heart muscles.
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Lyme disease or sarcoidosis.
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Ischemia of the heart.
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Bezold-Jarisch's condition reflects the increased vagal tone after myocardial infarction.
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Intake of drugs that slow the atrioventricular node and block the His-Purkinje fibers, for example, Flecainide.
What Are the Different Types of Atrioventricular Blocks?
There are several degrees of an atrioventricular block based on their severity, as mentioned below.
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Atrioventricular block of first-degree.
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Atrioventricular block of second-degree.
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Atrioventricular block of third-degree.
What Are the Differences Between the Types of Atrioventricular Blocks?
There are three types of atrioventricular blocks- first-degree, second-degree, and third-degree; and the following are the main differences between the three.
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First-Degree Block: Patients who suffer from the first-degree atrioventricular block are primarily asymptomatic. In case the diagnosis is delayed, they can present some clinical manifestations of weakness or dizziness.
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Second-Degree Block: Patients who suffer from second-degree atrioventricular block may or may not present any clinical signs or symptoms. For the ones who do come up with symptoms, they are mostly syncope and palpitations. In addition to these, their heart rates may also be elevated and may require some cardiac examination.
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Third-Degree Block: Patients with this degree of atrioventricular block are the ones who are suffering from a severe kind of heart block and need immediate treatment. The clinical features should be corrected before any organ damage or heart failure occurs. These patients need to go through multiple physical examinations, cardiac studies, and continuous monitoring till their conditions do not elevate. The exact location of the block has to be detected before the occurrence of a cardiac event such as a heart attack or cardiac arrest.
What Are the Signs and Symptoms of Atrioventricular Block?
AV block or atrioventricular block is of three different kinds defending the levels in their intensity as well as the location of the blockage. Due to this reason, the signs and symptoms vary according to the degree of the blocks and are specific to them.
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Patients who suffer from first-degree atrioventricular block present with shortness of breath, lethargy, and fatigue. It also happens that they show no symptoms at all.
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Patients suffering from second-degree atrioventricular block show signs of dizziness, syncope, and chest discomfort in addition to lethargy and fatigue.
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Patients who suffer from third-degree atrioventricular block have symptoms such as severe palpitations, lightheadedness, intolerance to exercise, difficulty in breathing, chest pain, and syncope.
How to Diagnose Atrioventricular Block?
Laboratory studies, electrocardiography, and other additional diagnostic modalities help in the diagnosis of atrioventricular block. Below are some of the diagnostic tools used for the diagnosis of atrioventricular obstruction.
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To check the presence of hyperkalemia, the electrolyte levels of the patient are checked.
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Levels of the drug Digoxin must be checked in case the patient is taking it.
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Potassium and any other drug toxicity should be evaluated.
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Electrocardiograph recording of 12-lead.
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An implantable loop recorder is also a vital tool in the diagnosis of atrioventricular block.
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Electrophysiological tests are done to find the location of the block and any other present arrhythmia.
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Echocardiography is done to evaluate the ventricular function of the heart.
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An exercise test is conducted to check if the heart condition improves or worsens during exercise.
How to Treat Atrioventricular Block?
There are multiple treatment modalities for the treatment of atrioventricular block. Some of these include pacemaker implantation or pharmacologic therapy.
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Pacemaker implantation is suggested where there is an irreversible condition of slow heart rate due to an atrioventricular block. These are used in chronic cases. A pacemaker helps in monitoring the heart rate, bradycardia, and any other symptoms in the long run.
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Pharmacological therapy is considered in addition to other drugs. A mixture of Isoproterenol and Atropine has been shown to improve the atrioventricular conduction during an emergency fall in heart rate caused by an atrioventricular block. Additionally, dopamine and occasionally Dobutamine have also proved to be effective during an emergency of an atrioventricular block.
Conclusion
An atrioventricular block is directly proportional to the degree of the underlying cardiovascular condition or any other medical problem. Patients with advanced atrioventricular obstruction need prompt treatment, while asymptomatic patients need monitoring. Cardiovascular collapse or syncope, along with congestive heart failure, are some of the complications of untreated and undiagnosed atrioventricular block. In case of any slight symptoms, the patient should seek immediate medical attention. Patient education is vital, and there should be aware of the reversible causes of atrioventricular block and thus avoid or limit those causes.
