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When Does Heart Block Need Pacemaker? Atrioventricular block (AV block), or commonly known as heart block, is a condition in which the heart's electrical impulses are partially or completely blocked as they travel from the upper cardiac chambers (the atria) to the lower cardiac chambers (the ventricles). If heart block is severe, it may slow the heart rate to dangerously low levels. In fact, heart block is one of the 2 major causes of bradycardia (slow heart rate). Brief episodes of heart block are not always dangerous. Transient heart block is frequently seen in young, healthy people who experience a sudden increase in the tone of their vagus nerves, often triggered by nausea, vomiting, or in response to pain, fright, or sudden stress. It usually disappears immediately once the triggering event has subsided. Nevertheless, heart block can be caused by heart attack, heart disease, coronary artery disease, myocarditis (inflammation of the heart muscle), cardiomyopathy (an enlarged heart), heart failure, and rheumatic fever. Sometimes heart block occurs because of injury to the heart during open heart surgery. Meanwhile, some people can be born with heart block and it is called congenital heart block.
General speaking, when a heart block is produced
by heart disease, pacemakers are likely required. Besides knowing their
patients’ causes of heart block, doctors need to know the symptoms they are
experiencing, the degree of heart block, and the specific location where heart
block occurs.
If heart block is producing symptoms like dizziness or syncope (loss of consciousness), then a pacemaker is usually necessary. The exception is when the heart block is known to be transient. If heart block is not producing any symptom, then probably no pacemaker is needed, unless it is one of the kinds of heart block that is likely to get worse over time. Heart block can be categorized into 3 degrees based on how severe it is. First-degree block means that each cardiac impulse eventually makes it from the atria to the ventricles, but the conduction of the impulse is slowed. In second-degree block, some of the impulses are successfully conducted to the ventricles, but some are not. All of the electrical impulses are blocked in people who have third-degree block. Third-degree heart block is also referred to as complete heart block. The degree can be determined with an electrocardiogram (ECG). The higher the degree of block, the more dangerous the heart block is likely to be, and the more likely one may need a pacemaker. Pacemakers are almost always needed with third-degree block, often with second-degree block, but rarely with the first-degree block. During the normal heart rhythm, the heart's electrical impulse must pass across the junction between the atria and the ventricles (the AV junction). This AV junction consists of AV node and HIS bundle. The HIS bundle can be considered as a compact cable of fibers that conduct electrical impulses from the AV node to the ventricles. In determining the severity of the heart block, it is important to know where in the AV junction the block is occurring. Location of heart block can be determined simply by examining the ECG for most cases. But sometimes an electrophysiology study is needed to locate where the block is. When heart block occurs within the AV node, the condition is usually mild and often does not require a permanent pacemaker. For heart block that happens within the AV node, subsidiary pacemaker cells in the AV node just beyond the site of the block often take over the rhythm of the heart, which is called a junctional escape rhythm.
On the other hand, any subsidiary pacemaker cells
in a person with a distal heart block (heart block occurs in or below the HIS
bundle) can only be located in the bundle branches or the ventricles. The
resulting heart rhythm is called a ventricular escape rhythm. Ventricular escape
rhythms are not only extremely slow but also unreliable. It is usually
considered as a medical emergency. Distal heart block tends to worsen over time.
So even in cases where it is currently causing only first or second-degree
block, distal heart block is dangerous, and virtually always requires treatment
with a pacemaker. Date: June 11, 2020
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