Heart block is the delayed or complete lack of electrical communication between the upper chambers of the heart (atria) and the lower chambers of the heart (ventricles). Normally, the ventricles are stimulated to contract by electrical impulses that travel through the conduction system from the upper-right chamber of the heart to the ventricles. If these impulses are delayed as they travel to the ventricles, an abnormally slow heart rhythm (bradycardia) could result. If these impulses are completely blocked from reaching the ventricles, they will fail to stimulate a heartbeat at all. In this case, secondary impulses may arise in the ventricles (producing ventricular escape beats). However, if no secondary beats arise, this situation will result in death without immediate treatment.
Type I second-degree heart block involves regularly occurring skipped beats, which patients may or may not notice. No other symptoms are generally reported, and the condition tends to resolve on its own.
Type II second-degree heart block may produce symptoms if the heart’s output of blood begins to decrease. These symptoms include dizziness or even fainting (syncope). Some people may feel confused or unsteady, or find that they are becoming easily fatigued. If any of these signs or symptoms are present, then treatment is warranted.
Third-degree heart block may produce any of the signs or symptoms associated with type II second-degree heart block, as well as symptoms somewhat like those preceding a heart attack. A patient is also at risk of convulsions and/or collapsing.
Certain factors may contribute to heart block. They include:
- Lack of oxygen-rich blood to the heart (cardiac ischemia), due to either blockages in the coronary arteries (coronary artery disease) or damage to the heart from a past heart attack.
- Electrolyte imbalances, such as high (hyperkalemia) or low (hypokalemia) levels of potassium.
- Disease or normal aging of the heart’s conduction system.
- Use of certain heart medications, such as beta blockers, calcium-channel blockers or digitalis (associated with first–degree heart block).
- Heart surgery
- Congenital heart condition
How it is Diagnosed:
The first step in diagnosing heart block is for a physician to obtain a patient’s complete medical history and to give the patient a complete physical examination. Blood tests may also be ordered to rule out electrolyte imbalances, or detect cardiac enzymes associated with a past heart attack or abnormally high levels of prescribed medications in the bloodstream. Next, the physician will order a common, painless test called an electrocardiogram (EKG). This test measures the heart’s electrical activity at rest. If heart block only occurs infrequently, it might not be picked up by tests during a scheduled office visit. Therefore, a holter monitor or event monitor may be ordered. These measures heart activity while the patient is “on the move” instead of in a physician’s office. The heart’s electrical activity is recorded on a portable tape inside the machine.
Depending on the results of the EKG and/or monitors, a physician may then order a test called an electrophysiology study. This test requires the insertion of several thin tubes (catheters) into veins (usually in the groin) from where they are guided to the heart. This test enables physicians to perform specific measurements of the heart’s electrical activity and pathways.
Type I second-degree heart block is generally treated by addressing any underlying conditions that are contributing to it. Temporary pacing and/or medication (e.g., atropine) may be required if the heartbeat is too slow, but a permanent pacemaker is generally not necessary unless the condition worsens.
Type II second-degree heart block often produces noticeable symptoms and carries a significant risk of potentially life-threatening complications. Therefore, treatment is very important. A physician may administer medications (e.g., atropine) and recommend the implantation of an artificial pacemaker. If the condition worsens to third-degree heart block, then a temporary pacemaker wire may be needed during the medical crisis until a permanent pacemaker can be inserted.
Third-degree heart block patients almost always require an artificial pacemaker to better regulate the electrical activity of the heart. If a medical crisis occurs before the pacemaker can be implanted, then a temporary pacemaker wire may be used to keep the heart beating. Most patients who are diagnosed with complete heart block will require placement of a permanent pacemaker, unless a treatable cause is identified and corrected.
What are the different types of heart block?
Type I second-degree heart block (also known as Mobitz Type I second-degree AV block or Wenckebach AV block). The electrical impulses are delayed longer with each heartbeat until a beat is skipped entirely. The source of the interference is usually within the AV node. The condition may sometimes cause dizziness.
Type II second-degree heart block (also known as Mobitz Type II second-degree AV block). Some of the electrical impulses are unable to reach the ventricles because of interference from somewhere below the AV node (e.g., the bundle of His). In contrast with type I second-degree heart block, this condition is generally less common and carries a higher risk of developing into complete (third-degree) heart block.
Third-degree heart block (also known as complete heart block or complete AV block). None of the electrical impulses can reach the ventricles, due to a problem that may lie anywhere between the atrioventricular node and the bundle branches, although the latter is more common. In the absence of any electrical impulses from the atria, the ventricles may generate some impulses on their own (called ventricular escape beats) via secondary impulse generators. However, these natural “backups” are usually very slow and are generally unable to sustain the full functioning of the heart muscle. Therefore, complete heart block poses a medical emergency with potentially severe symptoms.