Heart Block

The heart muscle is responsible for circulating blood throughout the body. When the heart does not operate as it is supposed to, and develops an abnormally slow rate that is less than 60 beats per minute, it can be due to a heart block.

A heart block occurs when the electrical current is delayed as it passes through the atrioventricular node, located between the heart's upper and lower chambers.

There are three types of heart block:

  • First degree - when there is only a fraction of a second delay in the electrical current as it goes through the atrioventricular node to the lower chambers (ventricles) of the heart.
  • Second degree - when the current is blocked intermittently and only some of the electrical impulses reach the lower chambers of the heart.
  • Third degree - when no current from the upper chambers of the heart reaches the lower chambers. In this case, the beating of the lower chambers is controlled by the atrioventricular node and is slower than the heart's normal pacemaker, the sinus or sinoatrial node. This causes a heartbeat that is often irregular and unreliable. Third-degree heart block is a serious arrhythmia that can cause fainting.
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Symptoms

Heart-block symptoms depend on the type of heart block present, and the degree to which the electrical current is interrupted.

First-degree heart block may produce no noticeable symptoms.

In second-degree heart block, the heartbeat may be slow, irregular or both.

In third-degree heart block, the ventricles (lower chambers) beat very slowly — less than 50 beats per minute or even as slowly as 30 beats per minute. This abnormally low heart rate can cause the brain and other organs to become oxygen-deprived, which can lead to symptoms such as:

  • Fainting
  • Dizziness
  • Fatigue
  • Weakness
  • Shortness of breath
  • Chest pain
  • Confusion
  • Memory difficulties
  • Quickly tiring during physical activity

The lower the heart rate, the more severe the symptoms will be.


Causes and Risk Factors

A variety of factors can cause heart block. Although the condition is most commonly diagnosed in older patients, first-degree heart block is common among well-trained athletes, teenagers and young adults.

Drugs, particularly ones that slow conduction of the electrical impulses through the atrioventricular node — such as beta blockers, diltiazem, verapamil and amiodarone — can increase the risk of heart block.

Having a highly active vagus nerve may also put patients at an increased risk of a heart block. This nerve is responsible for controlling the heart rate, moving food through the intestinal tract (gastrointestinal peristalsis), sweating, and several muscle movements in the mouth.

A history of certain diseases that affect the heart — including rheumatic fever and sarcoidosis — or other diseases that are caused by structural defects in the heart can increase a patient’s risk of developing heart block.

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Diagnosis

Diagnosis of a heart block will generally begin with the physician taking a medical history and performing a physical exam. During the physical exam, the physician will listen to the patient's heart to detect if there is an abnormal heart rate. If an abnormal heart rate is observed, the physician may order tests to examine the heart muscle, the blood flow through the heart, and any potential abnormal electrical impulses.

The most common diagnostic tool for a heart block is an electrocardiogram (EKG). This painless procedure provides a picture of the electrical activity of the heart and how the heart is working.

If the abnormal heart rhythm is intermittent, the patient may need to wear a Holter monitor. This portable device allows the medical team to observe the patient's heart activity over a longer period of time and helps diagnose the condition if the abnormal rhythm happens while the patient is not at the hospital.

Depending on the patient's symptoms and the results of other diagnostic tests, an echocardiogram may be prescribed. This noninvasive procedure uses a machine called a transducer that bounces sound waves off the heart and back into the transducer. These echoes are then translated into visual images.

Other diagnostics may include the tilt-table test and an exercise test to look at the relationship between the patient's heart rate and physical position (sitting or standing), as well as how exercise affects it. Electrophysiology studies may also be used to assess the electrical system of the heart.

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Treatments

Treatment of a heart block will vary depending on the type, severity and cause of the condition. In some cases, when the abnormal heart rhythm is caused by medications, treatment may focus on adjusting those medications. In other cases, surgery may be needed.

First-degree heart block generally does not need any treatment, even if it is caused by heart disease.

No treatment may be needed for some second-degree heart block cases if the patient does not have any symptoms. Depending on the severity of the symptoms, some patients with second-degree heart block may need an artificial pacemaker.

Almost everyone with third-degree heart block requires an artificial pacemaker. Third-degree heart block is generally diagnosed in an emergency situation, at which time a temporary pacemaker may be used until a permanent one is implanted. Most people who are given a pacemaker will need it for the rest of their lives — even if the heart rhythm returns to normal when the underlying cause of the heart block (such as a heart attack) is treated.

The knowledgeable and highly trained staff at the Cedars-Sinai Heart Institute will work with each patient to determine the best treatment option.