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Ann Thorac Surg 2002;74:792-796
© 2002 The Society of Thoracic Surgeons

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Original article: cardiovascular

Early postoperative arrhythmias after cardiac operation in children

^a Department of Pediatrics, University Children’s Hospital Zurich, Switzerland
^b Division of Cardiovascular Anesthesia, Institute of Anesthesiology, University Hospital Zurich, Zurich, Switzerland

Accepted for publication May 13, 2002.

* Address reprint requests to Dr Bauersfeld, University Children’s Hospital Zurich, Steinwiesstrasse 75, CH-8032 Zurich, Switzerland
e-mail: bauersfe{at}kispi.unizh.ch

	Abstract

Top Abstract Introduction Patients and methods Results Comment References

 
Background. Arrhythmias are a recognized complication of cardiac operations. However, little is known about the incidence, treatment, and risk factors for early postoperative arrhythmias in children after cardiac operations.

Methods. Diagnosis and treatment of early postoperative arrhythmias were prospectively analyzed in an intensive care unit in 100 consecutive children with a median age of 17 months (range, 1 day to 191 months) who had undergone cardiac operation. Patients were grouped in three different categories of surgical complexity.

Results. During a median postoperative time of 1 day (range, 0 to 15 days), 64 critical arrhythmias occurred in 48 patients. Arrhythmias consisted of sinus bradycardia in 30, atrioventricular block II to III in 7, supraventricular tachyarrhythmias in 14, and premature complexes in 13 instances. Treatment of 52 arrhythmias was successful and included pacing in 41, intravenous amiodarone in 8, body cooling in 5, overdrive pacing in 3, and electrolyte correction in 2 cases, with more than one treatment modality in 8 cases. Risk factors for arrhythmias were lower body weight (p < 0.05), longer cardiopulmonary bypass duration (p < 0.05), and a category of higher surgical complexity (p < 0.001).

Conclusions. Early postoperative arrhythmias occur frequently after cardiac operations in children. Sinus bradycardia, atrioventricular block II to III, and supraventricular tachyarrhythmias are the most frequent arrhythmias, which, however, can be treated effectively by means of temporary pacing, cooling, and antiarrhythmic drug therapy. Lower body weight, longer cardiopulmonary bypass duration, and a higher surgical complexity are risk factors for early postoperative arrhythmias.

	Introduction

Top Abstract Introduction Patients and methods Results Comment References

 
Postoperative arrhythmias are a known complication after open heart operation for congenital heart disease [1]. Many reports have been published about arrhythmias as late complication after cardiac operations such as the Mustard or Senning operation for transposition of the great arteries, Fontan procedures, or tetralogy of Fallot repair [2–5]. However, data concerning rhythm disturbances in the immediate postoperative period after open heart operation in children are scarce [1, 6]. Factors that may cause or increase the risk of postoperative arrhythmias are preexisting myocardial compromise by the cardiac defect, complex operation with extensive scars and suture lines, consequences of myocardial ischemia, postoperative electrolyte disturbances, and an increased adrenergic tone or catecholamine stimulation [7]. Arrhythmias that may be tolerated in a normal heart can be a major cause of morbidity and mortality after cardiac operation for congenital heart disease [7].

The aims of this prospective study were to assess the incidence of early postoperative arrhythmias after cardiac operation in a pediatric population, to describe their management, and to analyze possible risk factors.

	Patients and methods

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Patients
Between November 1998 and January 2000, 108 consecutive patients with a congenital heart defect underwent open heart operation with cardiopulmonary bypass (CPB) at the University Hospital Zurich. There were 8 perioperative deaths (7%), none related to arrhythmias; these patients were not enrolled in the study. Thus, 100 patients were evaluated prospectively during the entire stay in the intensive care unit (ICU), ie, from postoperative admission to discharge from the ICU.

For risk factor analysis, surgical procedures were classified as published previously into three categories of different operative complexity: low, moderate, and high (Table 1) [8].

Electrocardiographic monitoring
Standard electrocardiograms (ECGs) were registered in all patients at the time of ICU admission. Continuous ECG monitoring was performed during the entire ICU stay with Marquette Hellige SMU 612, Hellige SMV 110 TP, or Marquette Solar 8000 monitors (Marquette-Hellige, Marquette, WI). These monitoring systems did not provide storage and retrospective printing of the monitored ECG.

When an arrhythmia was detected on the ECG monitor, this was also documented with standard ECG. If standard ECG failed to provide adequate diagnostic information, an atrial ECG was recorded using the implanted temporary atrial pacing wires.

Arrhythmia definitions
Sinus bradycardia, frequent premature atrial or ventricular complexes, atrioventricular (AV) blocks, and supraventricular and ventricular tachycardias were considered critical arrhythmias. Sinus bradycardia was defined as an inadequate sinus rate for the age and hemodynamic condition of the patient or as a junctional escape rhythm in the absence of AV block or junctional ectopic tachycardia. As estimated normal heart rates are not applicable to children with cardiac dysfunction and in the postoperative state, higher sinus rates than normal were defined as adequate for the postoperative patients [9]. A minimal sinus rate of 120 beats/min in children younger than 2 years of age, and sinus rate of 100 beats/min in children older than 2 years of age were defined as adequate. Premature atrial or ventricular complexes were defined as frequent if occurring more often than 1 per minute [9, 10].

Arrhythmia management
Indications
Indications for treatment were sinus bradycardia, the presence of second-degree or third-degree AV block, and sustained supraventricular or ventricular tachycardias. Frequent premature atrial or ventricular complexes were treated in case of hemodynamic impairment. Hemodynamic impairment was defined as deterioration of one or more of the following variables: mean arterial blood pressure, mixed venous saturation, central venous pressure, or occurrence of acidosis.

Treatment
As potential causes of arrhythmias, electrolyte disturbances or adverse hemodynamic conditions were ruled out and corrected, if possible.

Patients with sinus bradycardia and AV block were treated by pacing using the temporary stainless-steel wire electrodes, routinely sutured on the epicardium of the right atrium and the right ventricle at the end of the operation. Termination of supraventricular reentry tachycardia was attempted with atrial overdrive pacing by using atrial stimulation protocols published previously [11].

Automatic tachycardias were treated primarily with body surface cooling to a rectal temperature of 32°C to 34°C using a cooling blanket, with the patient sedated and mechanically ventilated [12, 13].

Amiodarone was our drug of choice for the treatment of ventricular and supraventricular tachycardias resistant to overdrive pacing and automatic tachycardias unresponsive to cooling. Amiodarone was chosen on the basis of its well-documented antiarrhythmic potency, limited hemodynamic side effects, and good tolerance in children [11, 14]. Amiodarone was started with a loading dose of 5 mg/kg intravenously for 1 hour and continued with a continuous infusion at 10 to 15 µg/kg per minute. The oral administration was started with a 1-day to 2-day overlap with intravenous therapy [11].

Statistical analysis
Descriptive statistics are reported as median value and range. ² analysis and logistic regression models were used for the determination of independent risk factors for arrhythmias. A p value of less than 0.05 was considered statistically significant. Categories of surgical complexity, CPB duration, weight, and use of catecholamines were analyzed as potential risk factors for postoperative arrhythmias.

	Results

Top Abstract Introduction Patients and methods Results Comment References

 
The patient characteristics and the perioperative data of the different surgical categories are summarized in Table 2.

The diagnosis and frequency of arrhythmias are listed in Table 3. Supraventricular tachycardias consisted of intraatrial reentry tachycardias in 3 children, inappropriate sinus tachycardia in 1, ectopic atrial tachycardia in 2, and AV-reentry tachycardia in 1 patient. In 2 patients with supraventricular tachycardia we failed to make a more exact diagnosis as the tachycardia converted spontaneously before an ECG could be obtained. Ventricular arrhythmias were limited to isolated ventricular premature beats. We did not observe any ventricular tachycardia.

Treatment
Fifty-two arrhythmias, corresponding to 81% of all arrhythmias, were treated. Applied therapies for arrhythmias are summarized in Table 4. Combined treatment regimens were used in 8 patients.

Atrial overdrive pacing was successfully used for conversion of intraatrial reentry tachycardia in 3 cases. Cardioversion and defibrillation were not necessary in any case.

Body surface cooling was applied in 6 patients, including 2 with junctional ectopic tachycardia, 1 with atrial ectopic tachycardia, 1 with AV-reentry tachycardia, 1 with inappropriate sinus tachycardia, and 1 with intraatrial reentry tachycardia. Arrhythmia could be controlled with cooling alone in 3 cases of AV-reentry tachycardia, junctional ectopic tachycardia, and sinus tachycardia.

Antiarrhythmic drug therapy with amiodarone was used in 7 patients, including junctional ectopic tachycardia in 3, atrial ectopic tachycardia in 2, and intraatrial reentry tachycardia in 1. Amiodarone was effective in 6 cases. In spite of drug therapy, the patient with intraatrial reentry tachycardia could be converted only with repeated overdrive pacing. Intravenous amiodarone was administered during a median period of 5 days (range, 3 to 14 days). All 3 patients with junctional ectopic tachycardia received amiodarone only transiently, whereas therapy was continued in oral form for further prophylaxis in the other patients. We did not observe any short-term adverse effects attributable to intravenous amiodarone such as hypotension during drug loading or proarrhythmic effects. No changes were seen in liver or thyroid laboratory values.

Combined antiarrhythmic therapy was used in 7 patients. Body surface cooling and amiodarone were used in 1 case with junctional ectopic tachycardia, 1 with ectopic atrial tachycardia, and 1 with intraatrial reentry tachycardia. However, this last arrhythmia was finally converted by overdrive pacing. Overdrive pacing had to be performed additionally to drug therapy with amiodarone in another case with intraatrial reentry tachycardia. Antibradycardia pacing was applied after amiodarone therapy in the treatment of an ectopic atrial rhythm and together with body cooling in the treatment of 1 patient with junctional ectopic tachycardia. Finally, isoproterenol was given to a patient with sinus bradycardia, because of dysfunction of the pacing wires that were being used for 19 days.

Risk factor analysis
Independent risk factors for early postoperative arrhythmias were lower body weight (p < 0.05), prolonged CPB duration (p < 0.05), and a surgical category of high operative complexity (p < 0.001). Long CPB duration was found to be a risk factor for arrhythmias in the overall group of patients studied and in the patient group with moderate operative risk. In contrast, differences in CPB duration were not significant in the group with surgical procedures of low complexity and generally short CPB duration, and in the group with surgical interventions of high complexity and long CPB duration.

	Comment

Top Abstract Introduction Patients and methods Results Comment References

 
A large number of studies have been written about late-onset arrhythmias after cardiac operation [1–5]. Some other authors have focused their interest on the immediate postoperative period for specific cardiac defects or specific arrhythmias and treatments [6, 15–22]. This study presents data regarding the incidence of arrhythmias, their course, and the performed treatment during the ICU stay in a pediatric population after cardiac operation. Our assessment was intentionally not focused on specific lesions to provide broader information about the overall spectrum of rhythm disturbances potentially encountered by the pediatric cardiologist, cardiac surgeon, and critical care specialist in the immediate postoperative period.

Our results demonstrate that arrhythmias are a frequent early complication after open heart operation for congenital heart disease, despite the advances in surgical and CPB techniques as well as myocardial preservation.

We observed an overall arrhythmia incidence of 48%, similar to the frequencies reported by other authors [6, 23, 24]. This high incidence, occurring in spite of all surgical technical improvements, can be explained by performance of more-complex surgical procedures in increasingly younger patients. The fact that we found lower body weight, long duration of CPB, and high-complexity surgical procedures to be risk factors for arrhythmias supports this explanation.

Pathophysiologic causes for early postoperative arrhythmias are various, including direct surgical injuries like myocardial incision, results of cannulation, sutures close to the conduction system, and acute changes of the intracardiac pressure caused by volume and pressure overload [1, 7]. Furthermore CPB with ischemia-reperfusion and the related cellular biochemical effects as well as medical interventions such as electrolyte shifts and catecholamine administration may affect the stability of the cellular membrane and result in an increased myocardial irritability and automaticity [12, 13]. The degree of myocardial damage and the possibly associated risk for arrhythmia can be demonstrated by measuring myocardial metabolites like troponin I [25].

All arrhythmias we observed in this study were transient, and their adverse hemodynamic effects could be limited with the therapies used. Thus no life-threatening episodes or death were related to postoperative arrhythmias. By this means, the increased quality of the postoperative intensive care enables early recognition and immediate treatment of potentially lethal rhythm disturbances. Among all treatments, temporary pacing and drug therapy with amiodarone were the most frequently used. Temporary pacing is crucial as a therapy as well as a diagnostic tool in cases of complex arrhythmias [19]. Regarding drug therapy, this study confirms the efficacy, safety, and absence of negative inotropic effects of amiodarone compared with class I antiarrhythmic agents [14, 21, 22].

The size of the population studied was limited to 100 patients. Nevertheless, statistical rules of thumb suggest that in a sample size of 100 subjects, four covariates can certainly be analyzed with sufficient reliability. Thus, from our data, lower body weight, long duration of CPB, and complex operation can be considered to be risk factors for developing arrhythmia soon after operation.

In conclusion, early postoperative arrhythmias are still a frequent complication after cardiac operation in children. However, aggressive and expeditious management can reduce morbidity and mortality. Particularly temporary pacing and drug therapy with amiodarone are effective and safe treatments for early postoperative arrhythmias.

	References

Top Abstract Introduction Patients and methods Results Comment References

 

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