A heart block causes the heart to beat irregularly or more slowly than normal, potentially stopping for up to 20 seconds at a time.
This is caused by a delay, obstruction or disruption along the pathway of the electrical impulses that travel to the heart, sometimes resulting from an injury or damage to the heart muscle or heart valves.
A heart block, unlike coronary heart disease, doesn’t affect the heart’s blood vessels. It does not usually require treatment, but could be related to underlying health conditions.
What Is A Heart Block?
A healthy human heart beats at about 60 to 100 times per minute. A single heartbeat is one contraction of the heart muscles, which pumps blood around the body.
Normally, every heartbeat is created by an electrical signal that starts in the heart’s upper right chamber (right atrium).
- The signal is produced in an area of specialized cells in the atrium called the sinus node.
- The electrical signal then moves down through the heart to the atrioventricular (AV) node, which is another cluster of specialized cells that are located at the centre of the heart between the atria and ventricles. The AV node is also referred to as the electrical relay station because of its function of slowing down the electrical signal before it passes to the lower chambers (ventricles) of the heart.
- From the AV node, the electrical signal travels to the ventricles along with the cluster of cardiac fibres embedded in the heart walls. These cluster of fibres are called an AV bundle which divides into the two branches, one for each ventricle. The bundles conduct the electrical impulses to the heart ventricles. When the signal reaches the ventricles, blood is then pumped into the body.
- In the case of a partial heart block, the electrical impulses that control the heartbeat are delayed or blocked, preventing the heart from beating regularly.
- A complete heart block is when the electrical signals halt completely. In such cases, the heartbeat will drop to as low as 40 beats per minute. Sometimes, a heart block makes it difficult for the heart to pump blood properly through the circulatory system, which affects the muscles and organs as they do not receive the adequate amount of oxygen needed to function.
Heart block typically causes lightheadedness, fainting, and palpitations. In severe cases, a heart block can cause heart failure. In the case of a sudden cardiac arrest, a heart block can also cause chest pain. Coronary heart disease, on the other hand, results when there is plaque build-up on the coronary arteries. This can cause angina (chest pain) or myocardial infarction (heart attack).
Types Of Heart Block
A heart block can be present right from birth (congenital), but most often heart blocks develop after birth. In general, the risk of acquired heart block increases with age, along with the incidence of heart disease. Keeping this in mind, heart blocks can be categorized into three types:
- First-degree heart block involves minor heartbeat disruptions, such as skipped beats. Depending on the severity of symptoms, treatment may not be required.
- Second-degree heart block occurs when the atrial pulse does not reach the ventricles, causing dropped or skipped beats. In this case, the patient may feel dizzy and may need a pacemaker.
- Third-degree or complete heart block is when electrical signals do not travel between the upper and lower chambers of the heart. This is very common in people suffering from heart disease. A pacemaker becomes essential in order to avoid a serious risk of a heart attack.
Who Is At Risk Of A Heart Attack?
First-degree heart block is common among athletes, adolescents, young adults, and people with a highly active vagus nerve. People with a variety of heart diseases including , rheumatic heart disease or other structural heart disorders, are also at risk for developing a first-degree heart block.
In the case of an acquired heart block, the following conditions increase the risk:
- An enlarged heart or cardiomyopathy
- Heart failure
- Rheumatic fever
- Myocarditis, or inflammation of the heart muscle
- Endocarditis, or inflammation of the heart valves
- Acute or sudden heart block may also occur after a heart attack or a heart operation. It can also occur as a complication of Lyme disease.
- Injury to the heart during open-heart surgery, as a side effect of some drugs, or after exposure to a toxin.
Symptoms Of Heart Block
Abnormal heart rhythm is a change in either the speed or the pattern of the heartbeat. It may beat too slowly (bradycardias), too fast (tachycardias) or irregularly. Some abnormal heart rhythms occur in one of the atriums and are called atrial, others occur in the ventricles and are called ventricular. If a person has a heart block, they may experience the following symptoms:
- Lightheadedness or dizziness
- Palpitations (skipping, fluttering or pounding in the chest)
- Chest pressure or pain
- Shortness of breath
- Fainting spells
- Difficulty in doing exercise, due to the lack of blood being pumped around the body
Most cases of heart block respond well to timely intervention. Depending on your age and medical history, a heart specialist or cardiologist will be able to diagnose your symptoms with an electrocardiogram (ECG), echocardiogram or an electrophysiology test.