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(Circulation. 1995;92:283-285.)
© 1995 American Heart Association, Inc.

Articles

Congenital AV Block

Pace Me Now or Pace Me Later?

Richard A. Friedman, MD

From the Texas Children's Hospital, Houston.

Correspondence to Richard A. Friedman, MD, Texas Children's Hospital, The Lillie Frank Abercrombie Section of Pediatric Cardiology, 6621 Fannin St, Houston, TX 77030.

	Introduction

Top Introduction Present Study Questions Left Unanswered References

 
Congenital complete atrioventricular block (CCAVB) has been recognized for almost 100 years. First described by Morquio¹ in 1901, it has been of interest in the past primarily because of the risk of Stokes-Adams attacks or sudden cardiac death in these patients.^{2 3 4 5 6} As a result of some of these studies^{4 5 6} and others,^{7 8} the Committee on Pacemaker Implantation published the American College of Cardiology/American Heart Association Task Force Report in 1991⁹ with specific indications for implantation of a pacemaker in the presence of CCAVB. Although this syndrome is not diagnosed solely in children, the section under which these guidelines appear is "Indications for Permanent Pacing in Children." This certainly makes sense from the perspective that this disease is congenital in nature and initially recognized in childhood. With the advent of fetal echocardiography, in utero diagnosis of CCAVB has resulted in earlier intervention in newborns. Heightened suspicion of the possibility of CCAVB in children born to mothers with connective tissue disease, especially systemic lupus erythematosis, has had the same consequence.

To those faced with making the difficult decision of when to implant a pacemaker in an infant or child, arbitrary guidelines can be of concern. Should an asymptomatic newborn be referred for a pacemaker if the average heart rate when awake is found to be 58 beats per minute, or must this be done only if it is less than the recommended value of 55 beats per minute? What is the best plan for a 6-year-old referred to the clinic because of a murmur recognized during a school physical examination in whom complete AV block incidentally happens to be found on the ECG? The child's parents give a history that the child seems "normal" to them in terms of keeping up with the other children. An exercise test cannot be performed because of the child's age, but a Holter monitor demonstrates an average heart rate when awake of 48 beats per minute. During sleep, the heart rate slows to 28 beats per minute, but there is no history of sleep disturbance. An echocardiogram is normal, although the left ventricular end-diastolic dimension is at the upper limits of normal. Does this child need a pacemaker? Both of these examples are intentionally given with heart rate values just above the recommended levels for implantation. In clinical practice, these dilemmas seem to be the rule rather than the exception.

Adult patients with CCAVB typically do not give histories of "exercise intolerance." Upon specific questioning, however, many of them have adapted to a much more sedentary lifestyle as a result of their lifelong bradycardia. Some older adolescents with CCAVB may be very active, even playing varsity sports. A physiological result of the need for augmented stroke volumes in adapting to high levels of exercise may be a dilated heart on echocardiogram. It may be very difficult to recommend a pacemaker in this setting for an "asymptomatic" patient who seems to be doing fine.

	Present Study

Top Introduction Present Study Questions Left Unanswered References

 
The report in this issue of Circulation by Michaelsson et al¹⁰ is the largest series of patients with CCAVB who have been followed to study the long-term natural history of this disease for the purpose of determining who is at risk for sudden cardiac events. Some of the key points in this article are as follows.

1. Complete AV block and the presence of a prolonged QT_c interval requires intervention. It is vital for the clinician to measure the QT_c interval in the presence of AV block. Three of the seven patients with this diagnosis died in this study. Although one of the three who died eventually received a pacemaker, two did not; all four survivors were paced. The value of this therapy is the elimination of bradycardia as a trigger for the initiation of ventricular tachycardia. This group of patients probably represents an entirely different population whose risk factors include those associated with ventricular arrhythmias associated with congenital long-QT syndrome. While this is not new information,¹¹ the validation of this recommendation bears the reinforcement given with these data.

2. Sudden death may be the initial manifestation of congenital AV block, even in previously asymptomatic patients. Of the nine deaths in this study, five were sudden, with no preceding symptoms. In addition, five more patients required cardiac resuscitation. The fact that these events occurred at varying ages ranging from adolescence to late adulthood negates the assumption that the young, symptomatic patient is the only high-risk patient who warrants pacemaker implantation.

3. Exercise testing may be of limited value in risk assessment for future sudden cardiac events. Of the 76 patients who underwent exercise testing in this study, 22 (29%) had frequent ventricular ectopy with high work loads. Subsequent syncope or presyncope occurred in 14 (64%) of those patients. However, another 15% of the 76 patients who underwent exercise testing eventually had syncope or presyncope but had reasonable heart rates at rest and with exercise and no ventricular ectopy. Serial exercise testing might have yielded a higher specificity and sensitivity in the latter group, and this is a valid argument for regular reevaluation. It has been demonstrated that resting heart rate may not be predictive of exercise bradycardia or exercise intolerance.¹² Therefore, further information would be garnered by use of measurements of oxygen consumption (which was not routinely performed in this study) to help assess cardiac output during exercise.

4. Early intervention with pacing therapy in the asymptomatic patient may prevent the occurrence of significant myocardial dysfunction in later life. The development of significant mitral regurgitation occurred in 15% of the patients in this study, although this was not strictly quantified. The diagnosis of AV block was generally made early in these patients (newborn to 14 years), and the diagnosis of mitral regurgitation was made late (13 to 48 years) after diagnosis. In each case, the heart rate observed at the time of diagnosis was lower than the acceptable rate for age and would currently prompt a recommendation for implantation of a pacemaker.

Risk stratification of the patient who has reached adulthood may be quite different from identifying the infant or child who is at risk of a Stokes-Adams attack or sudden death. This argument is similar to that used for identifying the high-risk infant or child, compared with the adult, with Wolff-Parkinson-White syndrome or long-QT syndrome; the truly high-risk patients may "drop out" of the population (ie, die) before reaching adulthood, thus skewing the risk stratification to the low side compared with the population who present in infancy. Data that first identify the patient with CCAVB in late adolescence or adulthood may be limited in terms of drawing conclusions for the recommendation to implant a pacemaker in a young child. In this study, patients were added to a registry of a database of patients from 1964 only if they had passed the age of 15 without symptoms.

An interesting subgroup of patients in the present study who deserve special mention are those with a wide QRS rhythm. There were eight patients in the study with bundle branch block: four with right and four with left bundle branch block. Of the group of eight patients, three had Stokes-Adams attacks, but apparently none of these patients died. Furthermore, the other five patients remain asymptomatic, and none of these patients were reported to have received a pacemaker. Presently, when evaluating a patient with a wide QRS rhythm and CCAVB block, we assume that this represents a ventricular escape rhythm rather than junctional rhythm and bundle branch block. The current recommendation, supported by Michaelsson's article, is to pace all of these patients.⁹ The basis of this recommendation was a study by Pinsky et al,⁵ who reported on one patient with a documented wide QRS escape rhythm and sudden death due to a Stokes-Adams attack. Further support is referenced in a study by Driscoll et al,¹³ who made recommendations on patients with postoperative AV block and congenital heart disease. All of the deaths in the present study occurred in patients with narrow QRS escape rhythms. A wide QRS rhythm per se has not definitely been shown to be predictive of sudden death in CCAVB.

	Questions Left Unanswered

Top Introduction Present Study Questions Left Unanswered References

 
Although the present study helps to define risk in older patients with CCAVB, it leaves many questions unanswered. At what point should we recommend pacemaker implantation in an asymptomatic infant or child? Epicardial implantation of pacemakers in newborns is routinely performed at our institution by use of a limited subxiphoid approach. The atrium is easily accessible, and we usually implant a dual-chamber device. A small but definite morbidity and mortality associated with these operations must be taken into account. Is dual-chamber pacing really necessary in the infant or young child, or is single-chamber pacing sufficient until the child is older?

Is a recommendation for prophylactically pacing all adolescents with CCAVB at the time of diagnosis justified? From the present report, it seems that we can probably prevent sudden cardiac events (syncope or sudden death) by following this advice, excluding the occurrence of pacing system failure. However, we must take into account that although the true denominator is unknown, many of these patients do well without pacemakers. One approach would be to refine methods to identify patients who are at risk. This would include a thorough history to find the mildly symptomatic patients, including those with sleep disturbances, daytime inattentiveness due to fatigue, a history of very sedentary lifestyles, and other subtle symptoms of suboptimal cardiac output. Echocardiographic demonstration of enlarged left ventricular end-diastolic dimensions, severe left ventricular hypertrophy, and abnormal wall stress measurements may help define the subset of patients who need a pacemaker. Ambulatory monitoring and exercise testing are still useful. Finding increasing ventricular ectopy with exercise or multiform premature ventricular contractions and/or ventricular tachycardia on Holter monitoring would prompt pacing therapy. The present study may be one of the last to track the natural history of CCAVB. Available technology of small implantable pulse generators and leads has allowed the pediatric cardiologist to alter the natural history by implementing pacing therapy early in many patients.

The psychological impact of pacemaker implantation in a child must be taken into account. This is especially true of the adolescent who may have to significantly alter his or her lifestyle as a result of this intervention. The 14-year-old boy whose life revolves around playing varsity football may suddenly withdraw emotionally as a result of this activity being curtailed. The issue of body image and the desire to "be like everybody else" is quite strong at this age and will be affected by the surgical scar and protuberance on the chest. A sensitive approach with proper education and reassurance is critical when making this recommendation. Resentment of the presence of a pacemaker is not unusual for patients at this age. Anticipation of this problem by a physician with training and ability to deal with children and young adults who demonstrate this behavior is essential.

	References

Top Introduction Present Study Questions Left Unanswered References

 

1. Morquio L. Sur une maladie infantile et familiale caractérisée et la aorte subite. Arch Med Enfants. 1901;4:467.
   
2. Molthan ME, Miller RA, Hastreiter AR, et al. Congenital heart block with fatal Stokes-Adams attacks in childhood. Pediatrics. 1962;30:32-41. [Abstract/Free Full Text]
   
3. Nakamura FF, Nadas AS. Complete heart block in infants and children. N Engl J Med. 1964;270:1261-1268.
   
4. Karpawich PP, Gillette PC, Garson A Jr, et al. Congenital complete atrioventricular block: clinical and electrophysiologic predictors of need for pacemaker insertion. Am J Cardiol. 1981;48:1098-1102. [Medline] [Order article via Infotrieve]
   
5. Pinsky WW, Gillette PC, Garson A Jr, et al. Diagnosis, management and long-term results of patients with congenital complete atrioventricular block. Pediatrics. 1982;69:728-733. [Abstract/Free Full Text]
   
6. Dewey RC, Capeless MA, Levy AM. Use of ambulatory electrocardiographic monitoring to identify high-risk patients with congenital complete heart block. N Engl J Med. 1987;316:835-839. [Abstract]
   
7. Winkler RB, Freed MD, Nadas AS. Exercise-induced ventricular ectopy in children and young adults with complete heart block. Am Heart J. 1980;99:87-92. [Medline] [Order article via Infotrieve]
   
8. Benson DW Jr, Spach MS, Edward SB, et al. Heart block in children: evaluation of subsidiary ventricular pacemaker recovery times and ECG tape recordings. Pediatr Cardiol. 1982;2:39-45. [Medline] [Order article via Infotrieve]
   
9. Dreifus LS, Fisch C, Griffin JC, et al. Guidelines for implantation of cardiac pacemakers and antiarrhythmia devices: a report of the American College of Cardiology/American Heart Association Task Force on Assessment of Diagnostic and Therapeutic Cardiovascular Procedures (Committee on Pacemaker Implantation). J Am Coll Cardiol. 1991;18:1-13. [Medline] [Order article via Infotrieve]
   
10. Michaelsson M, Jonzon A, Riesenfeld T. Isolated congenital complete atrioventricular block in adult life: a prospective study. Circulation. 1995;91:442-449.
    
11. Escher E, Michaelsson M. Q-T interval in congenital complete heart block. Pediatr Cardiol. 1983;4:121-124. [Medline] [Order article via Infotrieve]
    
12. Reybrouck T, Vanden Eynde B, Dumoulin M, et al. Cardiorespiratory response to exercise in congenital complete atrioventricular block. Am J Cardiol. 1989;64:896-899. [Medline] [Order article via Infotrieve]
    
13. Driscoll DJ, Gillette PC, Hallman GL, et al. Management of surgical complete atrioventricular block in children. Am J Cardiol. 1979;43:1175-1180.[Medline] [Order article via Infotrieve]
    

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