Rhythm Disturbances in Children With Down Syndrome who Underwent Surgery for Congenital Heart Defects

Abstract

Background: Down syndrome is the most common chromosomal abnormality in live-born infants, and approximately 40% to 60% of children with Down syndrome are diagnosed with congenital heart defects. Corrective cardiac surgery can be performed in these individuals with good outcomes. In this study, we aimed to determine the incidence and outcomes of postoperative arrhythmias in patients with Down syndrome who underwent cardiac surgery. Methods: We conducted a retrospective analysis of patients < 18 years of age who were diagnosed with Down syndrome and had cardiac surgery between 2008 and 2023 at two tertiary cardiac centers. Results: Of 328 total patients, the most frequently encountered lesions were complete atrioventricular septal defect (145/328, 44%), ventricular septal defect (85/328, 26%), and partial atrioventricular septal defect (38/328, 11%). The incidence of postoperative arrhythmias was 24% (87 events in 80 patients). Of these arrhythmias, 27/87 (31%) were tachyarrhythmias (junctional ectopic, atrial ectopic, and reentrant paroxysmal supraventricular tachycardia) and 60/87 (69%) were bradyarrhythmias. These included third-degree atrioventricular [AV] block (n = 56) and sinus node dysfunction (n = 4). Twenty-four patients required permanent pacemaker implantation for persistent postoperative AV block (7% of all the study group cohorts). This incidence was higher than the reported incidence of 1% to 3% in the literature and higher than that in infants without Down syndrome who underwent cardiac repair at our two centers (2.4%). Conclusion: Children with Down syndrome who undergo cardiac surgery have a higher incidence of complete AV block requiring permanent pacemaker implantation when compared to children without Down Syndrome. This information is important for the preoperative counseling of families of these patients and postoperative planning.

Keywords

congenital heart disease arrhythmia pediatric congenital heart surgery

Introduction

Down syndrome, also known as trisomy 21, is the most common chromosomal abnormality in live-born infants, with an incidence of 1 in 700 to 800 live births.¹ Compared with the genetically typical population, individuals with Down syndrome have an increased incidence of congenital heart disease (CHD).^2,3 Approximately 40% to 60% of newborns with Down syndrome are diagnosed with congenital heart defects, the most common of which are atrioventricular septal defects (AVSD), ventricular septal defects (VSD), isolated atrial septal defects (ASD), and patent ductus arteriosus (PDA).⁴ Corrective cardiac surgery can be performed in these individuals, with good postoperative outcomes.^5,6 However, previous studies have reported a higher incidence of postoperative complications in children with Down syndrome.⁷

Arrhythmias are a recognized complication in children who undergo congenital heart surgery, with the incidence reaching 60% in some reports.^8,9 Although most postoperative arrhythmias are transient and treatable, they can have a significant effect on postoperative morbidity and mortality.^10,11 These arrhythmias occur in a vulnerable situation of hemodynamic instability; therefore, they are associated with prolonged mechanical ventilation and intensive care unit (ICU) and hospital stay as well as higher mortality rates.¹² Fudge et al reported a higher rate of complete heart block (CHB), requiring pacemaker implantation in patients with Down syndrome postoperatively¹³; however, there are limited data on the arrhythmia burden in patients with Down syndrome and its effects on the postoperative course. Therefore, this study aimed to examine the incidence and clinical outcomes of postoperative arrhythmias in patients with Down syndrome.

Methods

In this retrospective review, data were collected from two tertiary care cardiac centers between January 2008 and December 2023 after obtaining institutional review board approval. Informed consent was waived due to the retrospective nature of the study. Children (age ≤18 years) who were diagnosed with Down syndrome and underwent cardiac surgery were included. Patients with incomplete data, those who underwent surgery after 18 years of age, and those with preoperative arrhythmias were excluded.

Data Collection

Data were collected from the patients’ electronic health records including baseline demographic and clinical characteristics (age [in months] and weight at the time of surgery) sex, CHD type, and risk stratification using the Risk Adjusted classification for Congenital Heart Surgery [RACHS] scale).^14,15 Preoperative clinical status was noted and documented including preoperative critical care admission, the presence of preoperative pulmonary hypertension (PHTN), presence of arrhythmia, and the preoperative use of antiarrhythmics. The following intraoperative and postoperative details were collected: type of surgical intervention, cardiopulmonary bypass time, cross-clamp time, circulatory arrest time, intraoperative complications, ICU stay (in days), mechanical ventilation duration (in days), length of hospital stay (from the day of surgery to the day of discharge from the hospital), cardiac function in the first 24 h, and postoperative complications (low cardiac output syndrome, unplanned surgery or catheter intervention during the same admission, extracorporeal membrane oxygenation, stroke, acute kidney injury with or without dialysis, chylothorax, and any other complications such as neurological, hemorrhagic, or metabolic complications). In addition to postoperative mortality, the following data regarding postoperative arrhythmias (if present) were recorded: type of arrhythmia, date of onset and termination, method of control (pacing, antiarrhythmic drugs, and cooling), requirement of permanent pacemaker implantation, and rhythm at the time of discharge and at last clinic visit.

Definition of Arrhythmia

Sinus bradycardia requiring temporary pacing, second- and third-degree atrioventricular (AV) blocks, and sustained supraventricular and ventricular tachycardias were considered critical arrhythmias. Sinus bradycardia not requiring intervention and premature atrial or ventricular complexes without sustained supraventricular or ventricular runs were not considered clinically significant arrhythmias.

Arrhythmia tracings (electrocardiograms and rhythm strips) and parameters used to determine the diagnosis and successful control were reviewed whenever available, but no changes were made to the conclusions established by the treatment center.

Arrhythmia control was defined as either the restoration of sinus rhythm or the achievement of acceptable rate control (heart rate <160 beats/min or one standard deviation above the upper end of the age-adjusted reference range for the heart rate). In patients with junctional ectopic tachycardia, slowing the junctional rhythm to allow hemodynamic improvements with atrial or AV sequential pacing was considered successful arrhythmia control.

Permanent pacemaker implantation was performed in patients who had a third-degree AV block beyond the seventh postoperative day. The late-onset postoperative AV block was defined as third-degree AV block occurring 30 days after surgery.¹⁶

In this study, PHTN was defined as a pulmonary arterial pressure greater than 40 mm Hg at rest on echocardiographic evaluation or diagnostic cardiac catheterization. Pulmonary hypertension was diagnosed using transthoracic echocardiography by estimating the peak systolic gradient of the shunt between the ventricles using the Bernoulli equation in patients with intracardiac defects or a tricuspid regurgitation velocity greater than 2.9 m/s. In patients with PDA, we placed a shunt between the aorta and the pulmonary artery.

Inotropic Score and Vasoactive-Inotropic Score

Hourly doses of dopamine, dobutamine, epinephrine, norepinephrine, milrinone, and vasopressin were recorded for the first 24 h after postoperative admission to the ICU. In this study, the inotropic score (IS) was calculated as described by Wernovsky et al.¹⁷ The formula was expanded to include other vasoactive agents commonly used in current practice to define the vasoactive-inotropic score (VIS), as described by Davidson.¹⁸

The maximum VIS during the first 24 h was calculated as follows:

IS = dopamine dose (μ g / kg / \min) + dobutamine dose (μ g / kg / \min) + [100 \times epinephrine dose (μ g / kg / \min)]

VIS = IS + [10 \times milrinone dose (μ g / kg / \min)] + [10, 000 \times vasopressin dose (U / kg / \min)] + [100 \times norepinephrine dose (μ g / kg / \min)]

Acute kidney injury was defined as a more than 50% increase in the serum creatinine level from baseline values during the entire duration of stay in the ICU, according to the Pediatric Risk, Injury, Failure, Loss, and End-Stage Disease criteria.¹⁹ Baseline serum creatinine levels were measured as part of routine preoperative screening.

Prolonged length of stay was defined as hospital stay duration greater than the 75^th percentile of the duration of the overall cohort; in this study, it was found to be greater than or equal to 22 days.

Statistical Analysis

Data were analyzed using SPSS v25.0 (IBM Corp.). Continuous variables are expressed as means ± standard deviation or medians and interquartile ranges (IQRs), depending on the normality of distribution determined by the Shapiro-Wilk test. Categorical variables are presented as frequencies and percentages. Variables were evaluated using a bivariate analysis for associations with arrhythmias. Chi-square or Fisher exact tests were used for categorical variables, and the Mann-Whitney U test was used for numerical variables. The Kruskal-Wallis test was used to compare more than two independent categorical variables. Statistical significance was set at P < .05, and all tests were two sided.

Results

The demographic and clinical characteristics of the patients are summarized in Tables 1 and 2. Overall, 328 patients with Down syndrome underwent surgical repair for CHD (165/328 males, 50.3%). The overall median age at the time of surgery was seven months (IQR, 5.0-12.0 months), and 263/328 (80.2%) patients were younger than one year. The most common types of CHD were AVSD (145/328, 44%), VSD (85/328, 26%), and partial AVSD (38/328, 11%).

Table 1.

Demographic and Clinical Characteristics of the Participants.

N = 328	Frequency	Percentage
Age
<30 days	3	0.9%
1-12 months	260	79.3%
>12 months	65	19.8%
Male	165	50.3%
Prematurity (<37 weeks of gestation)	10	3%
Weight (kg), mean (IQR)	6.5 (3.8-5.7)
Preoperative ICU stay (days)	24	7.3%
Preoperative arrhythmia	0
Preoperative pulmonary hypertension	75	23%
RACHS score
1	6	1.8%
2	263	80.2%
3	54	16.5%
4	0	0
5	2	0.6%
6	2	0.6%

Abbreviations: ICU, intensive care unit; IQR, interquartile range; RACHS, risk adjustment for congenital heart surgery.

Table 2.

Distribution of Diagnoses in Patients With Down Syndrome.

Congenital heart disease (n = 328)	Frequency (n)	Percentage (%)
ASD	11	(3.3%)
VSD	85	(26%)
AVSD	145	(44%)
pAVSD	38	(11%)
ToF	21	(6.3%)
ToF/AVSD	9	(2.7%)
Other	22	(6.6%)
PAPVC	1
AVSD/CoA	3
CoA	1
DORV	5
IAA/VSD	1
VSD/CoA	4
SAM	4
Left AV valve stenosis	1
MR	1
TGA/VSD/TA	1
ToF/CoA	1
Truncus arteriosus with IAA	1

Abbreviations: ASD, atrial septal defect; AV, atrioventricular; AVSD, atrioventricular septal defect; CoA, coarctation of the aorta; DORV, double outlet right ventricle; IAA, interrupted aortic arch; MR, mitral regurgitation; PAPVC, partial anomalous pulmonary venous connection; pAVSD, partial atrioventricular septal defect; SAM, subaortic membrane; TA, tricuspid atresia; TGA, transposition of great arteries; ToF, tetralogy of Fallot; VSD, ventricle septal defect.

Preoperatively, 24/328 (7.3%) patients were admitted to the ICU, and none of the patients in this study experienced preoperative arrhythmias. Risk stratification using the RACHS scale demonstrated that most patients were in the low-risk categories (RACHS-1, 6/328 (1.8%); RACHS-2, 263/328 (80.2%); RACHS-3, 54/328 (16.5%); RACHS-4, 2/358 (0.6%) and RACHS-6, 2/358 (0.6%).

During the postoperative period (until discharge or death), 193 postoperative complications were observed in 126/328 (38.4%) patients, and 67 developed more than one complication (Table 3). Postoperative arrhythmias were observed in 80/328 (24.4%) patients.

Table 3.

Postoperative Data of Patients Hospitalized for the Surgical Repair of Congenital Heart Defects (n = 328).

Variable	Frequency	Percentage
Vasoactive-inotropic score (mean)	7.0 (Range 0-25)
Prolonged mechanical ventilation (>72 h)	59	18%
Prolonged hospital stay >22 days	81	24.7%
Arrhythmias	80	24.4%
Postoperative complications:	126	38.4%
Low cardiac output syndrome	4	1.2%
Open sternum	14	4.2%
Stroke	5	1.5%
Acute kidney injury	42	12.8%
Chylothorax	20	6.1%
Arrhythmias	87	27%
Surgical reintervention within 30 days	12	3.6%
ECMO	6	2%
Death	5	1.5%
Postoperative follow-up duration (mean, months)	33.7

Abbreviation: ECMO, extracorporeal membrane oxygenation.

Postoperative Arrhythmias

Of the 80/328 (24.4%) patients with postoperative arrhythmias, seven developed more than one type of arrhythmia. Table 4 summarizes the types of postoperative arrhythmias observed in this study. Of the 87 occurrences of postoperative arrhythmias there were 56 episodes (64.4%) of complete AV block upon admission to the ICU from the operating room (see Supplementary Table S1), and it was the most commonly encountered arrhythmia in the study group. This did not include patients who had developed transient AV block on coming off bypass in the operating room and recovered to sinus rhythm before returning to the ICU.

Table 4.

Postoperative Arrhythmias in the Study Population.

Arrhythmia (total number of events)	87 events (in 80 patients)	Percentage
Complete heart block	56	64.4%
Junctional ectopic tachycardia	23	26.4%
Sinus node dysfunction (requiring intervention)	4	4.6%
Atrial ectopic tachycardia	3	3.4%
Paroxysmal SVT (AVRT or AVNRT)	1	1.1%

Abbreviations: AVNRT, atrioventricular nodal reentry tachycardia; AVRT, atrioventricular reciprocating tachycardia; SVT, supraventricular tachycardia.

Of the patients with arrhythmias, temporary pacing was required in 61/80 (76%) patients, antiarrhythmic drug administration was used in 9/80 (11%) patients, and permanent pacemaker implantation was required in 24/80 (30%) patients. The overall incidence of patients with complete AV block requiring permanent pacemaker implantation was 24/328 (7%). None of the patients with sinus node dysfunction required permanent pacemaker implant. A review of surgical records in the participating centers showed that the incidence of postoperative complete AV block requiring permanent pacemaker implantation in patients without Down syndrome in the same time period was 2.4%. Comparing this incidence with the cohort of patients with Down syndrome (7%), we found that the increased incidence of permanent pacemaker implantation in the Down Syndrome group was statistically significant (P < .001).

The mean follow-up time was 33 months (range 0.5-186 months). During that period, late-onset complete AV block was noted in two patients (at one and five months postoperatively, respectively). The first patient was asymptomatic and had presented for a routine first postoperative clinic visit where he was found to have complete AV block. He was completely asymptomatic. The second patient presented five months after surgery to the emergency room with poor feeding and lethargy, and electrocardiogram (ECG) showed complete AV block. Both these patients underwent permanent pacemaker implantation. Both patients had transient complete AV block postoperatively and recovered within less than seven days. Their postoperative ECGs after AV nodal conduction recovery showed a right bundle branch block with a normal PR interval and no axis shift. A third patient was noted to have second-degree AV block (Mobitz 1) at the six-month follow-up appointment. She also had transient postoperative AV block and recovered within seven days with right bundle branch block and left axis deviation. She is currently being followed closely and did not meet indications for pacemaker implant.

Patients who developed postoperative arrhythmias were more likely to be younger (Table 5). The RACHS-1 risk score, presence of PHTN, and cardiopulmonary bypass time did not significantly differ between patients who developed arrhythmias and those who did not. Patients who developed postoperative arrhythmias were more likely to have a postoperative stay longer than 22 days (41.3% vs 19.4%, P < .01), mechanical ventilation time longer than 72 hours (32.5% vs 13.3%, P < .01), and higher inotropic score (mean score 8.5 vs 7.0, P = .02) than those who did not develop postoperative arrhythmias (Table 5). There was no difference in mortality between the two groups.

Table 5.

Comparison of Postoperative Outcomes in the Arrhythmia and Nonarrhythmia Groups.

	Arrhythmia (n = 80)	No Arrhythmia (n = 248)	P value
Age	7.1 ± 4.4	14.8 ± 20	<.01
RACHS ≥3	17 (21.3%)	41 (16.5%)	.22
CBP time (mean)	110.6 ± 62.2	98.9 ± 44.4	.09
Inotropic score (mean)	8.5 ± 4.6	7.0 ± 4.5	.02
Mechanical ventilation >72 h	26 (32.5%)	33 (13.3%)	<.01
Pulmonary hypertension	20 (25%)	53 (21.4%)	.80
Acute kidney injury	20 (25%)	22 (8.9%)	<.01
Chylothorax	8 (10%)	12 (4.8%)	.03
Length of stay >22 days	33 (41.3%)	48 (19.4%)	<.01
Mortality	2 (2.5%)	3 (1.2%)	.35

Abbreviations: CBP, cardiopulmonary bypass; RACHS, risk adjustment for congenital heart surgery.

Discussion

Down syndrome is the most common chromosomal abnormality, with an incidence of 1 in 700 to 800 live births worldwide. The incidence of Down syndrome has increased by 30% in the past two decades.²⁰ The outcomes of patients who undergo congenital heart surgery have improved owing to advances in surgical techniques and improvements in perioperative care.²¹ Several large cohort studies have demonstrated no significant differences in mortality between patients with and without Down syndrome who underwent corrective cardiac surgery. However, the duration of postoperative mechanical ventilation and ICU stay has been reported to be significantly longer in patients with Down syndrome.^7,22

This study focused on the incidence of cardiac rhythm abnormalities in children who underwent surgical repair for CHD. The overall incidence of arrhythmias in this study group was 24.4%. Of these patients, 69% (n = 60) had bradyarrhythmias (third-degree AV block and sinus node dysfunction), with 24 requiring permanent pacemaker implantation, and 21% had tachyarrhythmias (junctional ectopic, atrial ectopic, and reentrant paroxysmal supraventricular tachycardia). The incidence of postoperative tachyarrhythmias was similar to that reported in previous large cohort studies.^9,23

CHB is a well-known complication of congenital heart surgery. The reported incidence of CHB requiring pacemaker implantation is 1% to 3%.^24–26 In this study, there was a total of 56 occurrences of postoperative AV block initially requiring pacing. Importantly, more than half of those patients recovered to sinus rhythm within 7 to 10 days, and 24 patients ultimately required permanent pacemaker implant (7% of the study cohort). Only two patients developed CHB late after discharge from the hospital at one and five months. None of the patients who had sinus node dysfunction required permanent pacemaker implant.

Our study shows a higher incidence of permanent pacemaker implant in patients with Down syndrome compared with the incidence reported in the literature. A review of surgical records in the participating centers showed that the incidence of a postoperative complete AV block requiring permanent pacemaker implantation in patients without Down syndrome was 2.4%, which is similar to that reported in the literature.²⁷ This higher incidence of AV block in patients with Down syndrome could be partially explained by the predominant anatomical phenotypes of CHD in patients with Down syndrome (VSD, AVSD, and partial AVSD), as surgeries involving the crux of the heart are more likely to result in CHB. However, Fudge et al reported a higher incidence of postoperative AV block in patients with Down syndrome who underwent VSD repair than in a matched group of patients without Down syndrome who also underwent VSD repair (2.9% vs 0.8%).¹³ A similar finding was reported by Tucker et al in an analysis of 4,432 patients in the Pediatric Cardiac Care Consortium (PC4) Database who underwent surgical repair for a perimembranous VSD.²⁸ Furthermore, the risk of requiring pacemaker implantation in patients with Down syndrome in the PC4 cohort was not associated with age or weight.²⁸

The reason for the higher risk of AV block in patients with Down syndrome is still unclear. Developmental abnormalities of the cardiac conduction system in patients with AVSD, the predominant congenital heart defect in those with Down syndrome, are well documented.^29,30 These include posterior displacement of the AV node, a long nonbranching bundle, and the lack of apposition of the inferior and superior parts of the right AV ring bundle, all of which potentially increase the vulnerability of the AV node to injury in patients with AVSD. However, this does not explain the high incidence of permanent CHB in patients with Down syndrome who underwent VSD repair or those with other CHDs. Future studies are needed to determine the cause for this increased risk in patients with Down syndrome.

Limitations

This retrospective cohort study was conducted at two centers. The study design may have inherent statistical limitations that could affect the conclusions regarding the statistical significance and limit the investigation of causes and consequences. However, the study sample included patients with Down syndrome of different ages and heterogeneous congenital heart defects. Including patients from more than one surgical center also limits the performance or surgeon bias. The distribution of cardiac surgical procedures performed in children with Down syndrome in this study is similar to that reported in other studies, with complete ASD and VSD repairs being the most common.^13,31 This improves the generalizability of our findings. Given the retrospective nature of the study, telemetry review was only available if rhythm strips were included in the chart, and as such transient arrhythmias not captured by tracings or 12 lead ECGs could have been missed underestimating the true incidence of arrhythmias (although likely not of clinical significance).

Conclusion

Cardiac arrhythmias are a common postoperative complication in patients with Down syndrome undergoing cardiac surgery. We found that the incidence of complete AV block requiring permanent pacemaker implantation was relatively high (7%) when compared to patients without Down syndrome. This is important for the preoperative counseling of families of these patients and postoperative planning.

Supplemental Material

sj-docx-1-pch-10.1177_21501351251333687 - Supplemental material for Rhythm Disturbances in Children With Down Syndrome who Underwent Surgery for Congenital Heart Defects

Supplemental material, sj-docx-1-pch-10.1177_21501351251333687 for Rhythm Disturbances in Children With Down Syndrome who Underwent Surgery for Congenital Heart Defects by Khadijah Maghrabi, MBBS and Mohammed Alhabdan, MBBS in World Journal for Pediatric and Congenital Heart Surgery

Footnotes

Abbreviations

Declaration of Conflicting Interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article.

Ethical Considerations

This study received ethical approval from the Institutional Review Boards of both participating centers (King Faisal Specialist Hospital and Research Center, Riyadh #2181224 and King Abdulaziz University Hospital #27722).

ORCID iD

Khadijah Maghrabi

Supplemental Material

Supplemental material for this article is available online.

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Supplementary Material

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