Pediatr Cardiol (2006) 27:564–568 DOI 10.1007/s00246-004-0629-1
Potential Additional Indicators for Pacemaker Requirement in Isolated Congenital Atrioventricular Block J.M.P.J. Breur Æ F.E.A. Udink ten Cate Æ L. Kapusta Æ N. Boramanand Æ M.I. Cohen Æ J.E. Crosson Æ L.J. Lubbers Æ A.H. Friedman Æ J.I. Brenner Æ V.L. Vetter Æ E.J. Meijboom
Received: 25 July 2003 / Accepted: 21 July 2004 Ó Springer Science+Business Media, Inc. 2006
Abstract Low heart rate is the predominantly used indication for pacemaker intervention in patients with isolated congenital atrioventricular block (CAVB). The aim of this study was to compare the difference in heart J.M.P.J. Breur (&) Department of Obstetrics, University Medical Center Utrecht, KE 04. 123.1 P.O. Box 85090, 3508 AB Utrecht, The Netherlands E-mail:
[email protected] Tel.: +43-1-476545551 Fax: +43-1-476545567 J.M.P.J. Breur Æ F.E.A. Udink ten Cate Department of Pediatric Cardiology, Wilhelmina Children’s Hospital/University Medical Center, 3508 AB Utrecht, The Netherlands L. Kapusta Department of Pediatric Cardiology, Children’s Heart Center, University Medical Center, Nijmegen, The Netherlands N. Boramanand Æ A.H. Friedman Department of Pediatric Cardiology, Yale–New Haven Children’s Hospital, New Haven, CT, USA M.I. Cohen Æ V.L. Vetter Department of Pediatric Cardiology, Children’s Hospital of Philadelphia, Philadelphia, PA, USA J.E. Crosson Æ J.I. Brenner Department of Pediatric Cardiology, The Johns Hopkins University Hospital, Baltimore, MD, USA L.J. Lubbers Department of Pediatric Cardiology, Academic Medical Center, Amsterdam, The Netherlands E.J. Meijboom Department of Pediatric Cardiology, University Hospital of Vaudois, Lausanne, Switzerland
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rates recorded with ECG and Holter monitoring between paced (PM) and nonpaced (NPM) patients with isolated CAVB before pacemaker implantation to identify additional predictors for future PM need. Retrospective evaluation of atrial and ventricular rates (electrocardiography) and minimal and maximal (Holter) heart rates in 129 CAVB patients prior to PM implantation (n = 93) was performed, and results are expressed in V adjusted for age and sex. The average V score for the atrial rate was 0.51 (n = 50) in the PM group and 0.60 (n = 22) in the NPM group (not-significant). The average z score for the ventricular (average) rate was 0.91 (n = 83) in the PM group and 0.93 (n = 33) in the NPM group (not-significant). Minimal heart rate was 0.94 (n = 61) in the PM group and 0.86 (n = 25) in the NPM group (not significant). Maximal heart rate was 0.96 (n = 61) in the PM group and 0.95 (n = 26) in the NPM group (not significant). Initial recordings of the average heart rate and the minimal and maximal heart rate recorded during Holter monitoring do not seem to predict future pacemaker need in patients with CAVB. Studies with exercise stress tests are needed to confirm these findings. Keywords Pacemaker therapy Æ Congenital heart block Æ Congenital atrioventricular block Æ Heart rate Æ Holter monitoring
Introduction Congenital atrioventricular block (CAVB) is an uncommon cardiac conduction defect occurring in 1 of every 15,000–20,000 live births [10]. Approximately two-thirds of these patients have isolated CAVB, and
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one-third have associated structural heart disease [13]. By the age of 18 years, 74% of isolated CAVB patients have met the AHA/ACC criteria for pacemaker (PM) implantation and eventually all isolated CAVB patients will probably meet these. Electrocardiography (ECG) and Holters (24-hour ambulatory electrocardiography) are two important diagnostic and monitoring instruments that may detect the need for a pacemaker implant [3, 5, 8, 11]. Low heart rate is the most common indicator for pacemaker therapy. We hypothesized that patients with low escape rates, indicative of PM therapy, are unlikely to be able to adequately increase their escape rate. Furthermore, we assumed that the inability of the AV-blocked heart to achieve an adequate maximal heart rate may serve as an additional indicator for PM therapy.
Methods
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Statistical Analysis The clinical characteristics of the PM and NPM group were compared using the t-test for continuous data and the chi-square test for noncontinuous data. A z score adjusted for age and sex was calculated for every available, atrial and ventricular rate recorded by EGG and every minimal and maximal rate recorded by Holter [1, 2, 6, 15]. For example, the z score for a 12-year-old boy with complete CAVB with an average heart rate of 59 beats per minute (bpm) is calculated comparing this heart rate to the average heart rate of a 12-year-old boy, which is 85 bpm [1]. In this way, heart rates of all age groups and both sexes may be compared. A z score of ±1 represents a heart rate of 1 standard deviation above or below the average heart rate for that specific age and sex. The first available (before a possible pacemaker implant) averaged z scores were compared between the PM and the NPM group and also within the PM group using a two-sample, t-test for independent groups; a p value of 0.05 was considered significant.
Patient Population The population comprised 129 patients with CAVB and normal cardiac anatomy diagnosed between 1972 and 1999 at six medical centers: Wilhelmina Children’s Hospital/University Medical Center, Utrecht; Children’s Heart Center/University Medical Center St. Radboud, Nijmegen, Academic Medical Center, Amsterdam; Johns Hopkins Hospital, Baltimore, MD; Yale–New Haven Children’s Hospital, New Haven, CT; and Children’s Hospital of Philadelphia, Philadelphia, PA. Heart block was defined by complete absence of conduction between the atrium and ventricle by echocardiography in the fetus or by ECG in the patient. Patients with metabolic or infectious causes of heart block were excluded from the study. Abstracted data include sex, birth weight, gestational age, hydrops, age at diagnosis of heart block, follow-up time, and mortality. All available ECGs and Holters were examined for minimal, average, and maximal atrial and ventricular rates. Age of PM implantation and indication(s) for this implantation were documented. Patients were included in a PM group or a nonpacemaker (NPM) group based on whether a pacemaker had been implanted at the end of the inclusion period. Data from the first available ECGs and Holters were compared between PM and NPM groups. Within the PM group, we examined whether differences existed in minimal and maximal heart rates between the first available Holters and the Holters that indicated the need for PM intervention (low heart rate, pauses, progressive bradycardia, and ectopy).
Results Table 1 shows the characteristics of the patient population. No major differences between the two groups could be established. All fatal outcomes in the PM group were caused by development of dilated cardiomyopathy. A total of 93 patients underwent pacemaker implantation. Indications for PM implantation were low heart rate (n = 53, ventricular rate < 50 bpm in an older child or < 55 bpm in the neonate), pauses (n = 15), syncope (n = 11), heart failure (n = 10), exercise intolerance (n = 9), progressive bradycardia (n = 8), ectopy (n = 3), and failure to thrive (n = 1) [8]. Note that some patients had multiple indications for PM therapy. The median age of PM implantation was 4 years 3 months (range, birth to 9 years). Figures 1–4 show atrial and ventricular and minimal and maximal heart rates in isolated CAVB patients. Each point in Figs. 1–4 represents the z score for a single measurement. All heart rates were abstracted after the diagnosis CAVB was made and before a possible PM implantation. In each of these figures, line shows the corresponding heart rate in a normal population for different ages [1, 2, 6]. The z scores, calculated from the difference between the heart rates of the isolated CAVB patient and the corresponding heart rates for that age and sex in a normal population, were averaged. Shown in Table 2. No significant difference could be established between averaged z scores of the PM and NPM groups for any of the rates compared.
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Table 1 Study group characteristics
Sex Birth weight Gestational age Hydrops Age diagnosis* Follow-up Age PM Mortality
(m/f) (g) (wks) (months) (months) (months)
All patients (n = 129)
Nonpaced patients (n = 36)
Paced patients (n = 93)
58/71 2960 (660) 38 (3) 2 (2%) 1 ( 6–204) 118 (77)
20/16 3072 (524) 39 (2) 1 (3%) 0 ( 5–204) 122 (95)
38/55 2890 37 1 2 116 60 3
3 (2%)
0
(724) (3) (1%) ( 6–176) (69) (61) (3%)
Data presented are mean values ± SD or number (%) of patients NS, no significant difference *Median (range), negative numbers indicating number of months prenatally
Fig. 1 Atrial heart rates for PM (diamonds) and NPM (Squares) groups. The average heart rate at different ages in a normal population is shown by the line
Fig. 2 Ventricular heart rates for PM (diamonds) and NPM (Squares) groups. The average heart rate at different ages in a normal population is shown by the line
Fig. 3 Minimal heart rate for PM (diamonds) and NPM (Squares) groups. The lower limit of the heart rates in a normal population at different ages is shown by the line
Fig. 4 Maximal heart rates for PM (Diamonds) and NPM (Squares) groups. The upper limit of the heart rates in a normal population at different ages is shown by the line
Discussion Low heart rate is a common observation in isolated complete CAVB, and although only 57% of the PM cohort received a PM on this indication, low heart rate was evident in all [7, 12]. A consequence of this low
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ventricular rate is an increase in atrial rate illustrated by positive z scores. Since the atrium is completely intact in isolated CAVB, it is obvious that the difference in atrial rate between the PM and NPM groups is not significant.
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Table 2 Z-scores for Heart Rates
attacks and subsequently sudden cardiac death [5, 11, 12]. Our study does not confirm these findings. All fatal outcomes (n = 3) of CAVB were in the PM group and were caused by the development of a dilated cardiomyopathy [9, 14].
ECG Holter
atrial rates ventricular rates minimal rates maximal rates
*NPM
PM
§p
0.56 0.93 0.86 0.95
0.51 0.91 0.94 0.96
NS NS NS NS
Data presented are Z-scores. *NPM non pacemaker group NS no significant difference PM pacemaker group §p p value
Several patients in this study had maximal heart rates at initial Holter monitoring, exceeding 100 bpm, which is exceptionally high for patients completely dependent on their escape rate. A number of these patients may simply have had an unusually high ideoventricular rate at one time during monitoring. All patients eventually developed complete heart block. However, some initially presented with an incomplete block, which might explain the high maximal heart rate observed during Holter monitoring. Finally, some patients may have experienced adrenalin-ehanced atrioventricular conduction, temporarily restoring atrioventricular conduction and resulting in higher than normal escape rates. A low maximal heart rate did not prove to be indicative for future PM need. However, the maximal heart rate achieved on ambulatory Holter monitoring is not necessarily reflective of chronotropic competence as in exercise stress test [4]. The absence of stress tests and/or confirmed exercise while attached to a ambulatory monitor is a limitation of this study. This may mean that the maximal possible heart rate for these particular patients has not been achieved. On the other hand, it may also indicate that these patients tend not to embark on strenuous exercise because of previous experience of their inability to perform maximally. However, the maximal heart rate may still predict future PM requirement. Better distinction between complete and partial block is necessary, as well as assurance that the maximal heart rate is achieved during the registration period. The absence of a significant difference between the minimal heart rates in the NPM and PM groups supports the presence of other determinants in the decision of who will receive a PM. Organized stress tests may answer this question in a more definite manner but have not been performed in all these patients. However, exercise stress tests are of limited value when performed in young children ( < 4 years), making ambulatory Holter monitoring the only available instrument to record heart rates over longer periods of time [16]. Other studies have proven low heart rate to be a risk factor for the development of Adam–Stokes
Conclusion Initial recordings of the average heart rate and the minimal and maximal heart rates recorded during Holter monitoring do not seem to predict future pacemaker need in patients with CAVB. Studies with exercise stress tests are needed to confirm these findings. Moreover, better distinction at initial recording between infants with complete and partial heart block is necessary.
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