What Is a Heart Block?
A heart block, also known as an atrioventricular block (AV block), is a disturbance in the electrical signals controlling the heart. The heart's electrical signals start in the upper chambers, also called the atria. A steady flow of these electrical signals is required for the normal functioning of the heart. These signals travel down the lower chambers of the heart (ventricles), triggering them to pump and flow blood from the heart into the lungs and to the rest of the body. Heart block occurs when electrical activity is obstructed between the atria and ventricles. Heart block can lead to a heart attack or other heart problems. In the case of a minor heart block, no treatment is required, whereas, in severe cases, a pacemaker is required to restore the heart's regular electrical activity.
What Causes a Heart Block?
A heart block results from a trauma affecting the electrical conduction of the heart muscles. The risk of heart block also increases with age. The following risk factors include
-
A history of a heart attack.
-
Structural problems of the heart.
-
Diseases of the heart valve.
-
High potassium levels.
-
Acute Rheumatic Fever - This condition develops when the streptococcal infection, especially of the throat, is not well treated.
-
Cardiac Tumors - Tumorous growth in various parts of the heart.
-
Hyperthyroidism - The thyroid gland secretes excessive thyroid hormones in this condition.
-
Lymphoma - This is a cancer of the lymphatic system.
-
Lyme's Disease - This is a bacterial infection that spreads by the bite of an infected tick.
-
Diabetes.
-
Hypertension or high blood pressure.
What Are the Types of Heart Block?
Heart blockages can be classified according to the severity of the blockage of the electrical conduction between the upper and the lower chambers of the heart. They are:
1. First Degree - In the first-degree heart blockage, the electrical signals slow down on moving from the upper to the heart's lower chambers. It commonly occurs in adults above 60 years of age.
2. Second Degree - It is of two types:
-
Type l - Type l heart block is also known as Mobitz Type I or Wenckebach's AV block. This is a relatively less severe second-degree heart block in which the electrical activity gradually slows to the point where the heart skips a beat.
-
Type ll - Type ll heart block is also known as Mobitz type ll. This occurs when several electrical signals fail to reach the ventricles, thus causing a slower and abnormal rhythm. This heart block is associated with heart diseases like myocardial fibrosis, a condition in which there is an excess deposition of collagen in the heart muscles due to hypertension or underlying heart disease.
3. Third Degree - Third-degree heart block is more severe than the other degrees. In this heart block, the electrical signals from the atrium are blocked from reaching the ventricles, making them beat independently. Thus the heartbeat becomes very slow and irregular, making it tough for the heart to pump blood to meet the body's requirements. This results in a feeble pulse or no pulse at all. Individuals with third-degree heart block have an irregular heartbeat and a medical emergency.
What Are the Symptoms of Third Degree Heart Block?
The symptoms of third-degree heart block include the following:
-
Dizziness.
-
Fatigue.
-
Confusion.
-
Pain or pressure in the chest.
-
Shortness of breath.
How Is the Third-Degree Heart Block Treated in an Emergency?
The third-degree atrioventricular (AV) block is a medical emergency, and the treatment is based on the amount of the block present. The foremost treatment for heart block is to stop any medications that might be causing the block, such as a few antihypertensive, antianginal, antiarrhythmic, and heart failure medications.
Hemodynamically unstable individuals having a complete heart block, electrolyte abnormalities, or one who is in complete heart block due to a drug overdose or myocardial infarction should be admitted to the intensive care unit (ICU). The first line of management for individuals with abnormally slower heart rates usually begins with the use of the drug Atropine, administered intravenously. Atropine is not effective in individuals who have undergone a heart transplant. Still, Atropine does not help much in increasing the heart rate in individuals with a complete heart block. Thus, Dopamine and Epinephrine can be used to treat slow heart rate as a temporary measure and may not be able to improve the person's heart rate in third-degree heart block. Individuals with a third-degree heart block usually require pacing. Pacing changes the timing and intensity of the heart's contractions with the help of specific devices. Transcutaneous pacing is one of the ways of pacing and is quite fast. A transvenous pacemaker can be used if transcutaneous pacing does not give good results.
In stable individuals, a permanent pacemaker placement is usually recommended. A pacemaker (cardiac pacing device) is a device placed within the chest that helps control the heartbeat. It is a small battery-operated instrument that generates electrical impulses and sends them to the heart chambers. Pacing may not work if untreated underlying diseases are causing the heart block. For example, in individuals with drug toxicity, the underlying cause should be treated first rather than attempting pacing.
Temporary pacing can be considered in individuals with acute myocardial infarction (heart attack) leading to heart block. In individuals with an occluded right coronary artery leading to acute inferior infarction, prompt restoration of the arterial perfusion might lead to the correct treatment of a complete heart block. Whereas, in the case of a heart block due to an anterior infarction is more likely to need permanent pacemaker placement.
Conclusion
The treatment of individuals with third-degree heart block depends on the cause and severity of the underlying condition. Treating a critical patient with a third-degree heart block requires coordination and communication between physicians, nurses, and auxiliary healthcare workers. The prognosis depends on the presence of the person's underlying disease and its severity. Complete heart block is sometimes reversible in conditions like acute myocardial infarction by restoring the blood supply to the heart and in Lyme disease by treatment with antibiotics. Complete heart block often occurs in inferior myocardial infarction than anterior myocardial infarction. The placement of a pacemaker in individuals with a third-degree heart block is a definitive treatment.
