History and Physical Examination
Most pediatric patients with postoperative complete atrioventricular (AV) block (AVB) have had intracardiac surgery for atrial septal defect (ASD) repair, ventricular septal defect (VSD) repair, valve repair or replacements, or other complex congenital heart surgery.
Some patients with surgical complete AV block develop weakness, syncope, or congestive heart failure; others may be asymptomatic. Most of these patients exhibit complete AV block by the time cardiopulmonary bypass ends or during the immediate postoperative period. Fortunately, many recover AV conduction within the first 7-10 postoperative days.
Rarely, postsurgical patients develop complete AV block weeks to months after surgery. Late recovery of AV conduction is less common.
Symptoms and signs
Symptoms consist of dizziness, exercise intolerance, syncope, failure to thrive (in infants), and congestive heart failure. Patients with infranodal block tend to be more symptomatic than those with higher block sites, because low intrinsic escape pacemakers are slower and less reliable than higher-level intrinsic pacemakers.
Typically, patients with complete AV block have bradycardia. However, if the escape heart rate is rapid enough to maintain adequate cardiac output and cerebral perfusion, patients are asymptomatic. These individuals usually present with heart rates of 50-60 beats per minute (bpm).
Conversely, if the heart rate is inadequate to maintain blood flow to the brain (usually < 50 bpm in children) patients may have syncopal episodes. If the escape pacemaker rate is inadequate, sudden death may ensue.
The clinical presentation of newborns with complete congenital AV block may range from hydrops fetalis at birth to asymptomatic presentation with heart rates increasing to 100 bpm upon stimulation (eg, when feeding, crying).
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This is an example of a normal finding on intracardiac electrophysiologic (EP) study. The surface electrocardiogram (ECG) is represented in different colors, with its corresponding intervals (ie, PR, QT) on top. A catheter with several electrodes is placed inside the heart, close to the superior vena cava–right atrial junction. This catheter records the sinoatrial node (SN) activity and is depicted here as the high-right atrial (HRA) deflection. Beneath the HRA intracardiac electrogram is the His-bundle intracardiac electrogram, which is recorded by the electrodes of a second catheter placed across the posterior aspect of the tricuspid valve. The His-bundle electrogram provides the most information about atrioventricular (AV) conduction. Three main deflections are present, with 2 intervals: (1) the A deflection corresponds to the activation of the low-right atrium, (2) the H deflection corresponds to the activation of the His-bundle before its branching into the Purkinje system, and (3) the V deflection corresponds to the activation of the proximal portion of the right ventricle. The atrium-His (A-H) interval represents the conduction time through the AV node. It shows the time elapsed between the activation of the low-right atrium (A) and the activation of the His-bundle (H), ranging normally from 50-120 milliseconds. The His-ventricle (H-V) interval is measured from the beginning of the H deflection to the beginning of the V deflection and represents the conduction time through the His-Purkinje system (normally 35-55 ms). Disease in the AV node prolongs the A-H interval, whereas disease in the distal conducting system prolongs the H-V interval.
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This is a Mobitz type II second-degree atrioventricular (AV) block. The surface electrocardiograph (ECG) shows normal PR intervals and a P wave that is not followed by a QRS (in this graphic, the first P wave does not conduct through the AV node). The intracardiac electrogram shows no His deflection (H) after the blocked A deflection. In this case, the escape rhythm originates higher in the AV node at a rate of 40-50 beats per minute and is fairly reliable. However, patients may report symptoms of bradycardia such as dizziness, fatigue, and syncope. Because this type of AV block may progress to complete or third-degree AV block, patients should be monitored regularly even in the absence of symptoms.
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This is a Mobitz type II second-degree atrioventricular (AV) block that may likely progress to a third-degree, or complete, AV block. The difference from the previous image is that, in this case, a His (H) deflection is present after the A deflection (the atrium-His [A-H] interval is maintained); however, no ventricle (V) deflection is present after the first H deflection. Therefore, in this case, the escape rhythm is slower than in the intracardiac electrophysiologic study of the patient in the previous image (< 40/min) and less reliable. This patient is more likely to receive a pacemaker because of the higher incidence of sudden death secondary to prolonged asystole.
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This is a 12-lead electrocardiograph (ECG) of a 2-year-old girl with first-degree atrioventricular (AV) block that progressed to a complete, or third-degree, AV block (which is shown here). Her mother brought her to the clinic with described symptoms of easy tiredness and refusal to walk more than 1 block, which was a dramatic change for this girl. A normal sinus rhythm is present (shown by upward P waves in leads I, II, and aVF) at a rate of 135 per minute, which is completely dissociated from the QRS at a rate of 67 per minute. The QRS is narrow at 100 milliseconds with a frontal axis of 62°. No ventricular hypertrophy is present by voltage criteria. Because of the narrow QRS and its escape rate, this ECG is interpreted as complete AV block with junctional escape rhythm.
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This is a 12-lead electrocardiograph (ECG) of a 2-year-old girl with first-degree atrioventricular (AV) block that progressed to a complete, or third-degree, AV block (see the previous image). This ECG was taken after dual chamber (DDD-R) pacemaker placement. Sinus P waves are present at a rate of 90 per minute, followed by a pacemaker spike that produces a wide QRS of 128 milliseconds. No spike occurs before each P wave, because this type of pacemaker senses the patient's own P waves and stimulates the ventricle afterward. Therefore, the patient's ventricular rate follows her physiologic needs by tracking the patient's own atrial rate. With a DDD-R pacemaker, if the patient develops sinus bradycardia, the pacemaker takes over and paces the right atrium at the programmed rate, which is followed by the ventricular stimulation, maintaining AV synchrony.
