Pediatric Sinus Node Dysfunction Clinical Presentation

  • Author: M Silvana Horenstein, MD; Chief Editor: Stuart Berger, MD   more...
 
Updated: Aug 13, 2010
 

History

In children with no structural heart anomalies, sinus node dysfunction (SND) is less common. These children are usually asymptomatic. Otherwise, they may report dizziness, fatigue, exercise intolerance, syncope, or shortness of breath with or without palpitations. Infants may present with poor feeding or easy fatigability, which may also be evident in toddlers and older children.

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Physical

Older patients with SND and no structural congenital heart defects may be asymptomatic in general, despite being bradycardic for their age. Conversely, they may present with signs and symptoms of congestive heart failure (CHF), especially those who have undergone a Mustard operation for transposition of the great arteries or a Fontan operation for a single ventricle. Infants with CHF secondary to SND may be tachypneic and may have signs of pulmonary congestion on auscultation (ie, wheezing and rales) and hepatomegaly. In addition, they may show evidence of failure to thrive, with weight below the fifth percentile.

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Causes

The etiology for most cases is unknown. Causes can be categorized as follows:

  • Nonsurgical causes
    • SND may be familial. An autosomal dominant pattern of inheritance has been described.
    • Emery-Dreifuss muscular dystrophy is an X-linked muscle disorder associated with SND and AV conduction defects. If AV conduction defects are present, sudden cardiac death may result unless treated with permanent pacing. Males and females may be affected with equal frequency.
    • SND may be idiopathic. However, this form is rarely seen in children, especially in those without CHD or previous heart surgery.
    • SND may be caused by CHD, independent of the effects of surgical procedures. Examples include sinus venosus atrial septal defect (ASD), Ebstein anomaly, and heterotaxy syndromes, particularly left atrial isomerism.
    • Inflammatory diseases (eg, myocarditis, pericarditis, rheumatic fever) can result in SND.
    • Animal models of congenital complete AV block have shown that maternal immunoglobulin G (IgG) inhibits SN pacemaker cells, as well as AV node cells.
    • SND results from inactivation of genes that code for units of channels that play a key role in the regulation of cardiac pacemaker activity:
      • Mutations in the cardiac ion channel gene SCN5A causes SND as well as other cardiac arrhythmias, including long QT syndrome, Brugada syndrome, idiopathic ventricular fibrillation, and progressive cardiac conduction disturbances.
      • Loss of function of a pacemaker channel that plays a key role in the automaticity of the SN has been associated with mutations in the HCN4 gene.
      • Animal studies have shown that increased expression of A(3)AR adenosine receptors in mice resulted in AV block and pronounced SND in vivo.[2] Also, homozygous mutant mice with a defect of klotho gene expression (kl/kl) developed sudden death under stress, associated with SND (conduction block or arrest).
    • SND may be caused by CNS disease, which is usually secondary to increased intracranial pressure with subsequent increase in the parasympathetic tone.
    • SND may be secondary to antiarrhythmic drugs (eg, digitalis [because of SN exit block], propranolol, verapamil, quinidine, procainamide, lidocaine, disopyramide, reserpine).
    • Hypothyroidism may cause SND.
    • Hypothermia may cause temporary SND.
  • Surgical causes, especially with operations involving the right atrium (RA)
    • Gradual loss of sinus rhythm occurs after the Mustard, Senning, and all varieties of the Fontan operation. This is thought to be secondary to direct injury to the SN during surgery and also due to later chronic hemodynamic abnormalities. Paroxysmal atrial tachycardias are frequently associated with SND, and loss of sinus rhythm appears to increase the risk of sudden death. Patients with transposition of the great arteries now undergo the arterial switch operation, which avoids the extensive atrial suture lines that lead to SN damage.
    • SND was described in 15% of patients who had undergone the Ross operation for aortic valve disease or complex left-sided heart disease 2.6-11 years earlier.[3] Other arrhythmias, such as complete AV block and ventricular tachycardia, were present as well after the Ross operation.
    • When repairing ASDs, especially sinus venosus ASDs, SND frequently occurs because of the proximity of the defect with SN tissue.
    • Patients who have undergone surgery for endocardial cushion defects (ECDs) may also have SND later.
    • SND may be caused by a Blalock-Hanlon atrial septectomy.
    • SND may occur after repair of partial anomalous pulmonary venous return (PAPVR) or total anomalous pulmonary venous return (TAPVR).
    • Cannulation of the superior vena cava (SVC), usually performed for cardiopulmonary bypass or extracorporeal membrane oxygenation (ECMO), may damage SN tissue.
    • Ischemic cardiac arrest may cause SND.
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Contributor Information and Disclosures
Author

M Silvana Horenstein, MD  Assistant Professor, Department of Pediatrics, University of Texas Medical School at Houston; Medical Doctor Consultant, Legacy Department, Best Doctors, Inc

M Silvana Horenstein, MD is a member of the following medical societies: American Academy of Pediatrics, American College of Cardiology, and American Medical Association

Disclosure: Nothing to disclose.

Coauthor(s)

Peter P Karpawich, MD  Professor of Pediatric Medicine, Department of Pediatrics (Cardiology), Wayne State University School of Medicine; Director, Cardiac Electrophysiology and Pacemaker Services, Children's Hospital of Michigan

Peter P Karpawich, MD is a member of the following medical societies: American Academy of Pediatrics, American College of Cardiology, American Heart Association, Heart Rhythm Society, Michigan State Medical Society, and Pediatric Electrophysiology Society

Disclosure: Nothing to disclose.

Specialty Editor Board

Paul M Seib, MD  Associate Professor of Pediatrics, University of Arkansas for Medical Sciences; Medical Director, Cardiac Catheterization Laboratory, Co-Medical Director, Cardiovascular Intensive Care Unit, Arkansas Children's Hospital

Paul M Seib, MD is a member of the following medical societies: American Academy of Pediatrics, American College of Cardiology, American Heart Association, Arkansas Medical Society, International Society for Heart and Lung Transplantation, and Society for Cardiac Angiography and Interventions

Disclosure: Nothing to disclose.

Mary L Windle, PharmD  Adjunct Associate Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: Nothing to disclose.

John W Moore, MD, MPH  Professor of Clinical Pediatrics, Section of Pediatric Cardiology, Department of Pediatrics, University of California San Diego School of Medicine; Director of Cardiology, Rady Children's Hospital

John W Moore, MD, MPH is a member of the following medical societies: American Academy of Pediatrics, American College of Cardiology, and Society for Cardiac Angiography and Interventions

Disclosure: Nothing to disclose.

Gilbert Z Herzberg, MD  Assistant Professor, Department of Pediatrics, Section of Pediatric Cardiology, New York Medical College; Consulting Staff, Department of Pediatrics, Sound Shore Medical Center

Gilbert Z Herzberg, MD is a member of the following medical societies: American Academy of Pediatrics

Disclosure: Nothing to disclose.

Chief Editor

Stuart Berger, MD  Professor of Pediatrics, Division of Cardiology, Medical College of Wisconsin; Chief of Pediatric Cardiology, Medical Director of Pediatric Heart Transplant Program, Medical Director of The Heart Center, Children's Hospital of Wisconsin

Stuart Berger, MD is a member of the following medical societies: American Academy of Pediatrics, American College of Cardiology, American College of Chest Physicians, American Heart Association, and Society for Cardiac Angiography and Interventions

Disclosure: Nothing to disclose.

References

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This 12-lead ECG is from an asymptomatic 10 year-old girl, which was brought to our attention because of the irregularity of the P-P intervals. This ECG shows sinus arrhythmia at a rate of 65-75 beats per minute. The P waves all originate from the sinus node because they have a positive axis (upright) in leads I, II, and aVF. The PR interval is 104 milliseconds, and the QRS is narrow at 86 milliseconds, with a normal axis of 64°. The corrected QT (QTc) interval measures 402 milliseconds. Therefore, this is a normal ECG.
Below is an ECG of a 2-year-old girl who was referred to the clinic by the pediatrician for evaluation of a heart murmur. This ECG shows atrial rhythm originating most likely from the lower left atrium (P waves are inverted in lead I and are positive in II and aVF, with a frontal axis of 124°). The PR interval measures 113 milliseconds, and the QRS is narrow at 90 milliseconds. Right ventricular conduction delay is shown, which is best seen in the precordial leads V1 and V2. The QRS frontal axis shows right axis deviation (reference range for a 2-year-old child is 0-110°). The patient does not have right ventricular hypertrophy by voltage criteria. The inverted T waves in V1 are a normal finding at this age. An echocardiogram showed a moderately sized atrial septal defect. Nonsinus atrial rhythm is not a synonym of sinus node dysfunction.
This is a 12-lead ECG from a 12-year-old boy with history of syncope. This patient was healthy until 1 month earlier, when he started to experience episodes of lightheadedness. The ECG shows sinus arrhythmia (bradycardia) at a rate of 50-79 beats per minute with a PR interval of 136 milliseconds. Two junctional escape beats are present after a prolonged pause. The QRS is narrow at 85 milliseconds with a normal frontal axis of 70°. The corrected QT interval (QTc) is 411 milliseconds. A later electrophysiologic (EP) study showed prolonged sinus node recovery time (SNRT) and sinoatrial conduction time (SACT). Because of the patient's symptoms and his sinus node dysfunction, he received an atrial pacemaker. If this 12-lead ECG had been recorded from an asymptomatic patient, the findings would be considered within normal limits and no further workup would be indicated. In this case, the lightheadedness and, ultimately, the syncope define sick sinus syndrome, with the patient requiring pacemaker therapy.
 
 
 
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