Most conditions of heart block in children are asymptomatic and do not require treatment. Heart blocks involve varying degrees of dissonance within the electrical system of the heart. In children, many of the causes are congenital and others are acquired.
Electrical Conduction of the Heart
The electrical impulses that travel through the heart muscle, or myocardium, cause the beating action of the heart. These impulses normally begin in the sinoatrial, or SA node, stimulating the atria or upper half of the heart to pump. Almost instantaneously afterward, the electrical conduction courses to the atrioventricular, or AV, node to excite the ventricular cardiac fibers to spark the beating of the lower half of the heart. From the AV node, these impulses then shoot down the ventricular septum, or the muscle wall separating the two lower chambers of the heart, to excite the ventricles. This sophisticated chain of impulses is called the electrical conduction system and can be monitored by electrocardiograms, EKG or ECG for short. One of the features of an ECG is called the P wave. This "wave" represents the depolarization or positive charge of the cardiac cells in the atria. Thus, it represents the electrical activity of both atria.
First-Degree Heart Block
First-degree heart block is characterized by an elongation of the P-R interval, which is the time between the P wave and the QRS complex. "Essential Pediatric Cardiology" states that first-degree heart blocks are relatively benign conditions presenting in approximately 6 percent of healthy newborns. Causes for first-degree blocks include viruses, rheumatic fever, hypothermia and metabolic abnormalities. A first-degree block can also be a normal occurrence during sleep. Treatment is usually unnecessary.
Second-Degree Heart Block Type 1
Second-degree heart block type 1, or Wenckebach, presents as a progressive lengthening of the space between the P wave and the QRS complex, resulting in a dropped P wave. This condition can also be a normal finding during sleep in some children. "Pediatric Critical Care: The Essentials" states that Wenckebach heart blocks can be found in otherwise healthy children. These blocks are usually asymptomatic. Myocarditis and medications such as digitalis are common causes of this condition. No treatment is usually necessary.
Second-Degree Heart Block Type 2
Mobitz type 2 heart blocks are second-degree atrioventricular blocks that lengthen the P-R interval in a fixed ratio not completely synchronous with the ventricular conduction rate. A less common condition, Mobitz type 2 blocks are indicative of more serious conduction problems. These blocks can progress to complete heart block and generally require intervention. The most common occurrence of Mobitz type 2 blocks is following surgery. Treatment is pacemaker implantation.
Complete Heart Block
A complete heart block is the total loss of the conduction between the SA and AV nodes. The causes in children can be separated into two categories: congenital and acquired. The most common congenital cause is maternal systemic lupus erythematous. Acquired causes include myocarditis, rheumatic fever, trauma and catheter-placement. Treatment is pacemaker implantation.
References
- "Essential Pediatric Cardiology"; Peter Koenig, M.D., et al.; 2004
- "Pediatric Cardiology"; Heart Block in Children: Evaluation of Subsidiary Ventricular Pacemaker Recovery Times and ECG Tape Recordings; Woodrow Benson, M.D., et al.; 1982
- "Pediatric Critical Care: The Essentials"; Joseph Tobias, M.D.; 1999
- "Pediatric Critical Care Medicine: Basic Science and Clinical Evidence"; Derek Wheeler, M.D., et al.; 2007
- "Moss and Adam's Heart Disease in Infants, Children, and Adolescents: Including the Fetus and Young Adult," 7th ed.; Arthur Moss, M.D., et al.; 2008
