Thursday, October 26, 2017

Congenital Complete Atrio-ventricular Block



Congenital complete AV block in children is most often caused by autoimmune injury of the fetal conduction system by maternally derived IgG antibodies (anti-SSA/Ro, anti-SSB/La) in a mother with overt or, more often, asymptomatic SLE or Sjögren syndrome. Autoimmune disease accounts for 60–70% of all cases of congenital complete heart block and ?80% of cases in which the heart is structurally normal.

Complete heart block is also seen in patients with complex congenital heart disease and abnormal embryonic development of the conduction system. It has been associated with myocardial tumors and myocarditis. It is a known complication of myocardial abscess secondary to endocarditis. It is also seen in genetic abnormalities including LQTS and Kearn-Sayre syndrome. It is also a complication of congenital heart disease repair.

Incidence:
The incidence of congenital complete heart block is 1/20,000-25,000 live births; a high fetal loss rate may cause an underestimation of its true incidence. In some infants of mothers with SLE, complete heart block is not present at birth but develops within the 1st 3–6 mo after birth.

Clinical Manifestations:
The arrhythmia is often diagnosed in the fetus (secondary to the dissociation between atrial and ventricular contractions seen on fetal echocardiography) and may produce hydrops fetalis. Infants with associated congenital heart disease and heart failure have a high mortality rate.

In older children with otherwise normal hearts, the condition is commonly asymptomatic, although syncope and sudden death may occur. Infants and toddlers may have night terrors, tiredness with frequent naps, and irritability. The peripheral pulse is prominent as a result of the compensatory large ventricular stroke volume and peripheral vasodilation; systolic blood pressure is elevated. Jugular venous pulsations occur irregularly and may be large when the atrium contracts against a closed tricuspid valve (cannon wave). Exercise and atropine may produce an acceleration of ?10–20 beats/min. Systolic murmurs are frequently audible along the left sternal border, and apical mid-diastolic murmurs are not unusual. Heart block results in enlargement of the heart on the basis of increased diastolic ventricular filling.

Diagnosis:

The diagnosis is confirmed by electrocardiography; the P waves and QRS complexes have no constant relationship . The QRS duration may be prolonged, or it may be normal if the heartbeat is initiated high in the AV node or bundle of His.

Prognosis:
The prognosis for congenital complete heart block is usually favorable; patients who have been observed to the age of 30–40 yr have lived normal, active lives. Some patients have episodes of exercise intolerance, dizziness, and syncope (Stokes-Adams attacks); this symptom requires the implantation of a permanent cardiac pacemaker. Pacemaker implantation should be consid-ered for patients who develop symptoms such as progressive cardiac enlargement, prolonged pauses, or awake heart rates of ?40 beats/min.

Management:

Cardiac pacing is recommended in neonates with low ventricular rates ( appx. 50 beats/min), evidence of heart failure, wide complex rhythms, or congenital heart disease.

Isoproterenol, atropine, or epinephrine may be used to try to increase the heart rate temporarily until pacemaker placement can be arranged. Transthoracic epicardial pacemaker implants have traditionally been used in infants; transvenous placement of pacemaker leads is available for young children.

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