Pediatric Third-Degree Acquired Atrioventricular Block


Background

To gain an understanding of pediatric third-degree acquired atrioventricular (AV) block (AVB), one must first understand the concepts behind AV blocks. In general, AV block refers to a conduction delay or interruption of the impulses generated in the atrium before they reach the ventricles. AV block may be transient or permanent, and the anatomic level at which it occurs varies. These features determine the clinical significance of this condition, which may range from none to severely symptomatic, including Stokes-Adams syncope, congestive heart failure, or sudden death. 

In children, the most common cause of permanent acquired complete AV block is surgery for congenital heart disease. The second most common cause is congenital heart disease associated with complete AV block. Other etiologies of acquired AV block are often reversible and include digitalis and other drug intoxications, viral myocarditis, acute rheumatic fever, Lyme disease, and infectious mononucleosis. Rarely, complete AV block can occur as a complication of radiofrequency catheter ablation or during a diagnostic or interventional cardiac catheterization procedure (such as device closure of atrial or ventricular septal defects). [1Metabolic mitochondrial disorders and myotonic dystrophies can cause progressive AV block.

In adults, aside from the etiologies mentioned for the pediatric group, other causes of complete AV block include myocardial infarction (especially inferior), coronary spasm (usually of the right coronary artery), and neoplasms (eg, cardiac mesotheliomas). Almost exclusive to adult patients are two degenerative diseases of the specialized conducting system: Lev disease and Lenègre disease.

The following image depicts a normal intracardiac electrophysiologic study.

This is an example of a normal finding on intracarThis 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.

See also Atrioventricular BlockPediatric Second-Degree Atrioventricular BlockPediatric Third-Degree Congenital Atrioventricular BlockFirst-Degree Atrioventricular BlockSecond-Degree Atrioventricular Block, and Third-Degree Atrioventricular Block.

Classification of Atrioventricular Blocks

Depending on the anatomic level at which the atrial impulse is interrupted before reaching the ventricles, the atrioventricular (AV) block (AVB) may be classified as first degree, second degree, or third degree. [2The term first-degree AV block is actually a misnomer, because nothing is blocked; instead, the conduction time of impulses from the atrium to the ventricles is prolonged (PR prolongation on ECG).

Second-degree AVB

Second-degree AV block occurs either when successive impulses from the atrium to the ventricles are progressively delayed until conduction failure occurs (ie, Mobitz type I second-degree AV block, Wenckebach periodicity) or when an atrial impulse fails to conduct to the ventricles without any measurable lengthening of the preceding PR intervals (ie, Mobitz type II second-degree AV block) (see the first image below). Prolongation of the His-ventricle (H-V) interval may predispose individuals to complete or third-degree AV block (See the second image below).

This is a Mobitz type II second-degree atrioventriThis 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.
This is a Mobitz type II second-degree atrioventriThis 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.

Complete/third-degree AVB

In complete or third-degree AV block, the conduction of sinus or atrial impulses is entirely interrupted at the level of the AV node, in the bundle of His, or it is associated with an aberrantly located anatomic AV node that precludes normal anatomic communication to the distal conduction tissue. The atria and ventricles depolarize independently of each other, and the ventricular rate is typically slower than the atrial rate. The surface electrocardiograph (ECG) may reveal either narrow or wide QRS configurations, depending on the location of the interruption and the foci of the escape pacemaker tissue. For example, the QRS is narrow if the escape rhythm is supra-His bundle, or it is wide if the escape rhythm is intra-His or infra-His bundle. Escape ventricular rhythms with narrow QRS may be more stable than those with wide QRS morphologies. See the following images.

This is a 12-lead electrocardiograph (ECG) of a 2-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.
This is a 12-lead electrocardiograph (ECG) of a 2-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.

Pathophysiology

The atrioventricular (AV) node is composed of specialized cells arranged in 3 zones: (1) the atrial-transitional junction, (2) the transitional-compact node junction, and (3) the nodal-His junction or penetrating His bundle. [3These regions display different electrical properties, such as slowing of AV conduction with progressively increasing atrial rates until conduction block occurs, which protects the ventricles from dangerously rapid rhythms during atrial tachycardias. Other properties of the AV nodal cells include their ability to pace the heart by producing "escape rhythms" in case of a block above their anatomic level. [4These specialized cells, however, may begin to beat faster than the sinus node and may produce tachycardia.

Complete AV block (AVB) may occur immediately when the AV node is injured by direct trauma during surgery or catheterization, by ischemia during a coronary event, and by myocardial inflammation and infiltration during a viral illness. This condition may also occur years after mediastinal radiation secondary to fibrosis.

Certain congenital defects may also be inherently associated with vulnerability towards developing spontaneous AV block because of anatomic alteration in the arrangement of the AV node to the proximal His-Purkinje conduction tissue. These defects include L-transposition of the great arteries, some forms of double-outlet right ventricle or AV canal defects in the setting of heterotaxy syndrome, and other congenital heart lesions.

Etiology

Following surgical procedures

Postsurgical complete atrioventricular (AV) block (AVB) is the most common cause for acquired AV block in children, resulting from trauma to the AV node at the time of surgery (ie, hemorrhage, ischemia, necrosis, inflammation, traumatic disruption). This condition may occur following repairs, including those for ventricular septal defect (VSD), L-transposition of the great arteries (especially), tetralogy of Fallot (TOF), aortic stenosis, and other forms of congenital heart disease. [5These patients not only have very slow heart rates, but they are also prone to asystole, with a high risk for sudden death if left unpaced.

Transient AV block has also been associated with junctional ectopic tachycardia (JET) following surgery for congenital heart disease. [6Risk factors for JET in this patient population included younger age at time of surgery, longer aortic cross clamping time, and surgical procedures in proximity to the AV node. [6]

Transient and permanent complete AV block has been reported during complicated catheter manipulation in a diagnostic cardiac catheterization or following transcatheter closure of ASD and VSD. [7]

Infections

Complete AV block may occur with systemic infections that cause myocardial inflammation and infiltration, such as diphtheria, Borrelia burgdorferi infection (Lyme disease), Chagas disease, Rocky Mountain spotted fever, Yersinia enterocolitica infection, infectious mononucleosis, bacterial endocarditis, and viral myocarditis.

Diphtheria

Diphtheria is an infection of mucous membranes or skin caused by Corynebacterium diphtheriae, of which certain strains produce the diphtheria toxin. This protein can cause myocarditis, polyneuritis, and other systemic effects. Myocarditis occurs in 10-25% of patients with diphtheria and may develop during the acute phase or after several weeks. This consists of varying degrees of heart block, including complete AV block and arrhythmias, such as atrial fibrillation, premature ventricular beats, ventricular tachycardia, and ventricular fibrillation.

Lyme disease

Lyme disease is caused by the tick-transmitted spirochete B burgdorferi. It begins with an expanding skin lesion known as erythema migrans. Within several days or weeks, the spirochete spreads hematogenously, and approximately 8% of patients develop cardiac involvement. The most common abnormality is fluctuating degrees of AV block (ie, first-degree, second-degree, and third-degree AV block). Other more diffuse forms of cardiac involvement include left ventricular dysfunction, cardiomegaly, or pancarditis. Cardiac involvement usually lasts for a few weeks, although it may recur.

Chagas disease

Chagas disease is an endemic zoonosis in certain regions of Central and South America. It is caused by the protozoan Trypanosoma cruzi and is transmitted by hematophagous triatomae insects (ie, reduviids). These insects become infected after sucking blood that contains parasites from vertebrate hosts (eg, birds, mammals). Parasites reproduce in the guts of reduviids, and infective forms are discharged with feces at the time of subsequent blood meals. Therefore, the second host becomes infected with parasites because of skin abrasions that have been contaminated with infected feces.

Symptomatic chronic Chagas disease becomes apparent years or even decades after infection. Right bundle branch block is the most common electrocardiographic (ECG) abnormality, but other types of AV block, including complete AV block, are frequently observed. Other forms of rhythm disturbances include premature ventricular contractions, tachyarrhythmias, and bradyarrhythmias. Cardiomyopathy results in right-sided or biventricular heart failure.

Inflammatory and coronary disease

Rheumatic fever

Rheumatic fever is an inflammatory disease that occurs from pharyngeal infection with group A streptococci, with multisystemic involvement. In acute rheumatic carditis, all the layers of the heart may be compromised. Although most patients with carditis are asymptomatic, some have valvular damage of the mitral and/or aortic valves that may produce regurgitation and even congestive heart failure. In terms of rhythm disturbance in patients with carditis, tachycardia disproportionate to the degree of fever and varying degrees of heart block may occur. The most common type of AV block is first degree.

Reiter syndrome

Reiter syndrome is a seronegative arthropathy that may be accompanied by pancarditis with involvement of the AVN (ie, varying degrees of AVB) and proximal aortitis with valve regurgitation. Both of these features are more common in patients with long-standing disease and peripheral joint involvement.

Sarcoidosis

Sarcoidosis is an inflammatory systemic disease characterized by formation of granulomas that most frequently affect the lungs, lymph nodes, skin, eyes, and liver. However, it may affect any organ. When it affects the heart, it may cause different types of conduction disturbance, from bundle branch block to complete AV block. [89Interestingly, the AV block may be reversible. [810Sudden death has been described.

Coronary ischemia and degeneration of the conducting system

Ischemia from acquired coronary disease (eg, Kawasaki disease) or from inferior wall infarcts can transiently or permanently damage the conduction tissue, leading to variable degrees of AV block.

Hypertension and aortic and/or mitral stenosis are believed to accelerate the degeneration of the conducting system through calcification and fibrosis.

Neuromuscular and neurocutaneous disease

Myotonic dystrophy forms 1 and 2

Myotonic dystrophy forms 1 and 2 are neuromuscular diseases inherited in an autosomal dominant fashion, with genetic anticipation, in which cardiac involvement consists of disorders of impulse formation and, especially, AV conduction. They are typically progressive and are caused by an expanded CTG repeat in the 3-prime untranslated region of the DMPK gene and by an expanded CCTG repeat in intron 1 of the ZNF9 gene, respectively. These diseases begin as asymptomatic PR prolongation and lead to complete AV block. Syncope and sudden death may occur; therefore, symptomatic patients require insertion of a permanent pacemaker. Diagnosis is mainly clinical.

Kearns-Sayre syndrome

Kearns-Sayre syndrome (also known as oculocraniosomatic disease) is a neuromuscular disease caused by a mitochondrial DNA deletion. Its characteristic triad includes progressive external ophthalmoplegia, pigmentary degeneration of the retina, and progressive cardiac conduction defects, including complete heart block. Other features may include ataxia, hearing loss, dementia, short stature, delayed secondary sexual characteristics, hypoparathyroidism, hypothyroidism, and peripheral neuropathy. The diagnosis is usually made clinically and by demonstration of ragged red fibers on skeletal muscle biopsy. Any progression in conduction abnormalities (such as from first- to second- degree AV block) is a clear indication for permanent pacemaker implantation in Kearns-Sayre syndrome, given the unpredictability of disease progression.

Tuberous sclerosis

Tuberous sclerosis is a neurocutaneous disorder caused by mutations in any of four separate genetic loci in which cutaneous lesions of multiple types are associated with tumors and malformations of the central nervous system (CNS). Mental retardation may be severe, and patients develop intractable seizures. Cardiac rhabdomyomas within the AV node may cause complete AV block and different types of rhythm disturbances, such as ventricular tachycardia when localized in the ventricles. Diagnosis is clinical. The earliest lesions are leaf-shaped hypopigmented spots scattered over the trunk and limbs; they are observed better using a Wood lamp than with the naked eye.

Degenerative disease

Almost exclusive to adult patients are two degenerative diseases of the specialized conducting system: Lev disease and Lenègre disease. In Lev disease, calcification and sclerosis of the cardiac skeleton frequently involve the mitral and aortic valves, the central fibrous body, and the summit of the ventricular septum. Lenègre disease is thought to represent a primary sclerodegenerative disease of the conducting system with no involvement of the myocardium or fibrous skeleton of the heart.

Intracardiac tumor

Intracardiac tumors constitute a very rare cause of acquired complete AV block that occurs through invasion of the conduction system. [11The term cardiac mesothelioma refers to heterotopic epithelial replacement of the AV node; it is a rare entity and, thus, a rare cause for complete AV block. Cases of congenital complete AV block and complete AV block in adults secondary to cardiac mesotheliomas have been reported. [121314151617Definitive diagnosis is made only at autopsy, upon which necropsy may reveal extensive infiltration of the AV node and proximal bundle by mesothelioma tissue. Metastatic melanoma has also been described to cause sudden complete AV block and sudden death. [1819]

Primary cardiac lymphoma has been described to cause complete AV block. [2021Case reports of sinus rhythm restoration after tumor remission have been described.

Abnormal protein deposition

Amyloidosis is a systemic disease in which abnormal production of immunoglobulins leads to their deposit in various tissues such as tongue, intestines, skeletal and smooth muscles, nerves, skin, ligaments, heart, liver, spleen, and kidneys. When the heart is affected, cardiomyopathy with marked left ventricular wall thickening, severely decreased systolic and diastolic function, and complete AV block may ensue. [222324]

Drugs, chest trauma, and irradiation

Drugs such as digoxin, beta-blockers, and calcium channel blockers may cause transient complete AV block, which can be fatal if the ventricular escape rhythm is inadequate to maintain brain blood flow or if asystole is prolonged.

Clonidine, tricyclic antidepressants, penetrating chest trauma, and radiation may cause complete AV block. Mediastinal radiation for lymphomas such as Hodgkin lymphoma has been described to cause complete AV block. 



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).



Diagnostic Considerations

Atrioventricular (AV) dissociation may be secondary to sinus or atrial bradycardia with a faster ventricular or junctional escape rhythm, in which appropriately timed atrial impulses conduct to the ventricles. The R-R interval changes when a sinus/atrial beat is conducted, as opposed to complete AV block (AVB) where R-R intervals do not vary.

AV dissociation with second-degree AV block varies from occasionally dropped sinus/atrial beats to occasionally conducted beats. In this last example, it may be hard to distinguish from complete AV block.

Transient postsurgical complete AV block is caused by edema of adjacent tissues. This resolves after 1-2 weeks.

Other conditions to consider when evaluating a child with suspected third-degree acquired AV block include rheumatic fever, Rickettsial InfectionRocky Mountain Spotted Fever, and Tuberous Sclerosis.

Differential Diagnoses



Approach Considerations

Lyme disease is diagnosed by its clinical picture and serologic confirmation. Serologic test findings may be negative during the first several weeks, but most patients have a positive antibody response to B burgdorferi by enzyme-linked immunoabsorbent assay (ELISA). In addition, B burgdorferi may be cultured from skin lesions during the acute phase or from skin lavage as it has been recently described.

Diagnosis of acute Chagas disease is made by microscopic examination of fresh anticoagulated blood to visualize the parasites. Whenever this technique is unsuccessful, xenodiagnosis can yield positive test results in virtually all patients with acute Chagas disease and in half of those with chronic disease. In this technique, uninfected reduviids feed on the patient's blood and, 30 days later, their intestinal contents are examined for the presence of parasites. In case of chronic Chagas disease, serologic tests to detect antibodies against T cruzi antigens, such as complement fixation and ELISA, are used.

The diagnosis of Reiter syndrome is mainly clinical, because no specific laboratory tests are used for this entity. However, nonspecific findings include elevated erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP), elevated immunoglobulin A (IgA), mild normochromic and normocytic anemia, and absent rheumatoid factor (RF) and antinuclear antibodies (ANAs).

Definitive diagnosis of diphtheria is made by isolation of C diphtheriae from local lesions.

Perform laboratory testing for lymphoma, amyloidosis, sarcoidosis, and digoxin as indicated.

Antenatal diagnosis of third-degree AV block requires careful maternal-fetal management and monitoring with ultrasonography and echocardiography. [29Delivery is recommended at a tertiary care center with a multidisciplinary team that includes perinatal care and an association with a pediatric cardiology center. [29]

Electrophysiologic Studies

Intracardiac electrophysiologic (EP) studies are usually not necessary for most patients with AV block; however, when performed, the EP results can be used to determine whether the AV block is above, within, or below the bundle of His.

EP studies are not required for patients with complete AV block and symptoms such as dizziness, syncope, or congestive heart failure. These patients require permanent pacemaker therapy. Indications for pacing are outlined in detail in the ACC/AHA/HRS consensus document.

Infra-His AV block

Patients with infra-His atrioventricular (AV) block typically have a much slower ventricular rate (ie, heart rate) and require permanent pacemaker therapy to avoid asystole, ventricular arrhythmia, syncope, or symptoms.

The block is located in the AV node above the His bundle when the ventricular depolarization is preceded by a His depolarization, which, in turn, is not coupled to the atrial depolarization.

The block is within the His bundle if the His bundle depolarization is preceded by an atrial depolarization, and a second His bundle depolarization precedes a ventricular depolarization.

The block is below the His bundle when the His depolarization follows an atrial depolarization but does not precede a ventricular depolarization.

Junctional/ventricular pacing

Adequacy of the junctional or ventricular pacemaker can be evaluated by pacing the ventricles at different rates for 30-60 seconds, stopping abruptly, and measuring their recovery time (ie, from the last paced ventricular beat to the first spontaneous ventricular beat). A junctional or ventricular recovery time exceeding 3 seconds in children is abnormal and has been associated with risk for sudden death.

See the following examples of intracardiac EP studies.

This is an example of a normal finding on intracarThis 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.
This is a Mobitz type II second-degree atrioventriThis 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.
This is a Mobitz type II second-degree atrioventriThis 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.

Approach Considerations

Treatment is focused on restoring atrioventricular (AV) sequential activation and/or maintaining a heart rate tolerated by the patient, which is assessed by the absence of symptoms. [30 Other measures include resuscitation, diagnostic testing, treating potential reversible causes, monitoring for progression, and assessing whether definitive pacemaker placement is required. [31]

Asymptomatic patients require no immediate pacemaker treatment, although these individuals should be closely monitored. If the escape rhythm slows, they may become symptomatic and require permanent pacemaker therapy. Indications for permanent pacing are outlined in detail in the American College of Cardiology Foundation, American Heart Association Task Force on Practice Guidelines, and the Heart Rhythm Society.(ACCF/AHA/HRS) expert consensus documents. [32333435]

Recognizing Lyme disease is important, because appropriate antibiotic therapy for 10-20 days with tetracyclines, erythromycin, intravenous penicillin, or ceftriaxone can often revert the complete AV block (in addition to preventing rheumatologic and neurologic symptoms).

Temporary Cardiac Pacing

In symptomatic patients with atrioventricular (AV) block, perform cardiac compressions, and administer catecholaminergic agonists (to accelerate the escape rhythm) while preparing for temporary cardiac pacing. Permanent cardiac pacing will be required if the AV block does not resolve.

Acquired AV block (AVB) from myocarditis, Lyme disease, and surgically induced trauma caused by adjacent tissue edema in patients with structurally normal hearts is usually transient and may not require therapy or may require only temporary pacing. However, in 40-55% of postsurgical patients, complete AV block persists beyond 7-14 days, and pacemaker therapy is indicated. [36]

In postoperative patients with intermittent AV block, externalized temporary cardiac pacing wires that can be attached to an external temporary pulse generator set at a predetermined rate to maintain adequate cardiac output is typically required.

In postoperative patients with persistent complete AV block lasting more than 7 days within or below the bundle of His, permanent pacemaker therapy is currently indicated. [37]

If the escape rhythm is less than 60 bpm in infants or 45 bpm in adolescents, permanent pacemaker therapy may be indicated to prevent symptoms, congestive heart failure, ventricular arrhythmias, or sudden cardiac death.

Temporary external cardiac pacing can also be performed in emergency situations, but it is not as effective as transvenous pacing and can also be uncomfortable if the patient is conscious.

Permanent Pacing

Patients with postoperative complete atrioventricular (AV) block (AVB) and those with Kearns-Sayre syndrome require prophylactic pacemaker therapy before symptoms develop because of the high risk for sudden death from asystole (> 60% in some series).

Regardless of symptoms or underlying escape rate, patients with postoperative complete AV block should always receive a permanent pacemaker system if the AV block persists more than 8-14 days and if no contraindications to pacemaker implantation are noted. [37However, the overall prevalence of postsurgical complete AV block lasting over 10 days has been reduced to 5%. Most patients with postoperative complete AV block recover AV conduction within the first 7-10 postoperative days. These pediatric patients do not require a permanent pacemaker if conduction has fully recovered.

Stanner et al evaluated the midterm results of epicardial pacemakers implanted in a retrospective review of 71 infants who underwent implantation between 2000 and 2017. They concluded epicardial pacemakers are safe for infants at least 5 years. However, battery depletion is a frequent occurrence due to stimulation at higher heart rates in infancy. [38]

Prophylactic pacemaker therapy is indicated for any patient with complete AV block with a wide QRS escape rhythm. [37Pacing is also indicated in patients with complete AV block who have exercise intolerance or other symptoms of chronotropic incompetence.

Dual-chamber pacemakers are currently preferred for patients who require life-time pacing. The preferred pacemaker modalities in most centers include the single-chamber pacing and dual-chamber sensing (VDD) [39and the dual-chamber pacing and sensing (DDD). [40These allow physiologic ventricular tracking of the atrial rate.

The long-term effects of asynchronous cardiac activation induced by right ventricular (RV) apical pacing have been described in patients with congenital complete AV block and normal cardiac anatomy. [41These effects included deleterious left ventricular (LV) remodeling, LV dilatation and asymmetric LV hypertrophy. [42However, pacing from the RV outflow tract decreases or slows adverse cardiac remodeling [43and improves hemodynamics. [44]

Cardiac resynchronization pacing (biventricular pacing) may reduce or reverse the effects of left ventricular dysfunction induced by chronic right ventricular apical pacing.



Medication Summary

In general, complete heart block is not amenable to medications. In emergent situations, for short-term use, catecholaminergic stimulation with isoproterenol infusion may be useful to maintain an adequate escape rate while awaiting placement of a temporary or permanent pacemaker. Medications which cause or exacerbate AV block should be discontinued whenever possible.

Beta1/Beta2 Adrenergic Agonists

Class Summary

These agents increase heart rate and contractility.

Isoproterenol (Isuprel)

Agents with combined alpha- and beta-selective properties may be necessary to maintain blood pressure.