Total heart block. Also known as Complete Heart Block, it consists of a complete failure of the conduction of all the impulses that leave the atria to the ventricles, so that they beat independently.
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- 1 General
- 2 Frequency
- 3 Pathology
- 4 Diagnosis
- 5 Forecast
- 6 Treatment
- 7 Sources
Heart block can be discovered at birth or during the first days of life and is presumed to be of congenital origin. In this age, the acquired form of the block is infrequent, which is occasionally observed in myocarditis and endocardial fibroelastosis .
Several hundred cases of suspected congenital heart block have been reported, however, this disorder is rare at or shortly after birth. On very rare occasions, the diagnosis of heart block before birth has been established.
The pathology of congenital heart block may be associated with other cardiac abnormalities or present as an isolated abnormality. In some cases there is no connection between the atria and the AV node, and in others the connection is intact, but the branched portion of the bundle of His is absent. Approximately 75% of infants with congenital heart block have no other heart defects. In those that do, corrected transposition and atrial defect are the most common abnormalities.
The presence of heart block before birth is suggested by the finding of persistent bradycardia at any time during the last trimester of pregnancy . It can be distinguished from bradycardia due to fetal distress by the regularity and persistence of slow heartbeat and by the absence of a significant alteration as regards the intensity of heart tones. Knowledge of this state and its discovery may prevent diagnosis error of fetal distress and unnecessary interruption of pregnancy.
The discovery of undoubted bradycardia during any of the first days of life is pathognomonic for congenital heart block. Although it is true that a delay in cardiac contraction can be observed during the first hours of life in some children with pale asphyxiation or severe intracranial injuries, bradycardia generally does not have the degree observed in congenital heart block.
In the latter, the frequency of the heartbeat is always less than 80 and often, up to 40 per minute. Other alterations may be lacking in the child , however this depends on the type and intensity of concomitant cardiac abnormalities. Children with severe disorders may present with cyanosis , cardiomegaly, and heart failure, however, bradycardia may be the only obvious sign of heart disease during the neonatal period, and the other signs may not manifest more than during early and second childhood. Bradycardia is often so mild that it is not discovered at the time of birth and is diagnosed later in life.
The electrocardiogram easily establishes the diagnosis. A complete type of congenital heart block is almost always observed in which the electrocardiographic curve will show atrioventricular dissociation and P waves that appear independent of QRS complexes. Atrial concentration is one to two times more frequent than ventricular contraction. On the other hand, the electrocardiogram shows a trace within normal limits, except when there are other heart defects.
The discovery of heart block in the very young child is of importance for the prognosis, because it means the presence of concomitant congenital heart disease , the latter may be so severe as to cause death in the first days of life. Most infants with block have a rate of 40 to 80 beats per minute.
In general, a heart rate below 40 justifies a poor prognosis, even if other heart defects are missing . With heart rates of this order, heart block does not in itself imply additional overload of the heart, however, very rarely a patient with heart block dies in the middle of a Stokes-Adams attack due to syncope, these accesses are rare in the second childhood and are hardly recognized in the first. In almost all cases, heart block persists throughout life, but occasionally varies in intensity. In one patient, heart block disappeared completely at the end of the first year of life. It remained normal in a group of patients followed by Campbell and Thorn for 25 years.
No treatment is necessary in cases of congenital heart block in asymptomatic infants. Infants with very slow heart rates and decreased cardiac output have a poor prognosis . In these cases, a pacemaker will be placed without delay