What is Heart Block (Atrioventricular Conduction Abnormalities)

Heart block pictureHeart block is a disorder of the electrical conduction system of the heart. There are three degrees of heart block:

  • 1st degree: There is a delayed conduction between the atria and ventricles, but all beats are conducted;
  • 2nd degree: Some beats from the atria are not conducted to the ventricles;
  • 3rd degree: The atria and the ventricles beat completely independently of each other.

Statistics on Heart Block (Atrioventricular Conduction Abnormalities)

First degree heart block is common, but is usually asymptomatic (without obvious signs or symptoms). Higher degrees can be common, particularly in elderly populations.

Risk Factors for Heart Block (Atrioventricular Conduction Abnormalities)

A previous heart attack (myocardial infarction) is the most common cause of heart block. It may also be caused by degeneration with fibrosis and calcification of the conducting system (Lev’s and Lenegre’s diseases). Other causative factors include drugs that interfere with conduction, electrolyte disturbances, cardiac surgery, pericarditis, myocarditis, cardiomyopathy and rheumatic heart disease.

Progression of Heart Block (Atrioventricular Conduction Abnormalities)

First degree heart block is by itself of no significance, provided it does not progress to second or third degree, but this does not often happen.

Most cases of second degree heart block are also asymptomatic, and these patients should be closely observed for potential progression to complete heart block.

In complete heart block no atrial impulses conduct to ventricular contraction. Spontaneous escape rhythms either from the ventricles maintain life in the person, but symptoms such as syncope (brief loss of consciousness) are usually seen.

Symptoms of Heart Block (Atrioventricular Conduction Abnormalities)

First degree blocks are never symptomatic and do not require any treatment. Symptoms of second and third degree heart blocks include awareness of the slow heart beat and syncope.

Clinical Examination of Heart Block (Atrioventricular Conduction Abnormalities)

The pulse is generally slow. With second degree heart block it may be regular or regularly irregular. With third degree heart block it is usually slow (<50) and regular.

How is Heart Block (Atrioventricular Conduction Abnormalities) Diagnosed?

Blood tests (U+Es) should be used to rule out electrolyte disturbances. Thyroid function testing to assess levels of thyroid hormones.

Prognosis of Heart Block (Atrioventricular Conduction Abnormalities)

This depends on the severity of the dysfunction and the nature of the arrhythmia. For first degree heart block the outlook is good as most are never symptomatic and require no treatment.

Most cases of second degree heart block need no treatment, but it is important to check with a specialist as some may need a pacemaker inserted in case it progresses.

Third degree heart block can cause cardiac arrest thus it should always be treated with a pacemaker.

How is Heart Block (Atrioventricular Conduction Abnormalities) Treated?

Treatment depends on the severity of the block, and whether or not symptoms are present. Any underlying cause of the heart block should be treated if possible. Ventricular pacing is the treatment of choice. Various options are available.

Heart Block (Atrioventricular Conduction Abnormalities) References

  1. Schlant RC, Alexander RW, Fuster V (eds). Hurst’s The Heart (8th edition). New York, NY: McGraw-Hill; 1994. Book
  2. Kumar P, Clark M (eds). Clinical Medicine (4th edition). Edinburgh: WB Saunders Company; 1998. Book