A wandering atrial pacemaker is a change in the morphology of the P waves with variable PR interval and normal QRS complex. This is a benign finding, requiring no further evaluation or treatment.
Premature atrial contractions are relatively common prenatally and in infants. A premature P wave, usually with an abnormal axis consistent with its ectopic origin, is present. The premature atrial activity may be blocked (no QRS following it), conducted normally (normal QRS present), or conducted aberrantly (a widened, altered QRS complex). Premature atrial contractions are usually benign and, if present around the time of delivery, usually disappear during the first few weeks of life.
Atrial flutter and atrial fibrillation are uncommon dysrhythmias in pediatrics and usually present after surgical repairof complex congenital heart disease. They may also be seen inpatients with myocarditis or in association with drug toxicity.
Supraventricular tachycardia (SVT) is the most common symptomatic dysrhythmia in pediatric patients. The rhythm has a rapid, regular rate with a narrow QRS complex. SVT in infants is often 280 to 300 beats/minute with slower rates for older children and adolescents. The tachycardia has an abrupt onset and termination. In a child with a structurally normal heart, most episodes are relatively asymptomatic other than a pounding heartbeat. If there is structural heart disease or the episode is prolonged (>12 hours), there may be alteration in the cardiac output and development of symptoms of heart failure. Although most patients with SVT have structurally normal hearts and normal baseline ECGs, some children have Wolff-Parkinson-White syndrome or preexcitation as the cause of the dysrhythmia.
Premature ventricular contractions (PVCs) are less common than premature atrial contractions in infancy but more common in older children and adolescents (Table 142-2). The premature beat is not preceded by a P wave and the QRS complex is wide and bizarre. If the heart is structurally normal, and the PVCs are singleton, uniform in focus, and disappear with increased heart rate. The PVCs are usually benign and require no treatment. Any deviation from the presentation (history of syncope or a family history of sudden death) requires further investigation and possibly treatment with antiarrhythmic medications.
Ventricular tachycardia, defined as three or more consecutive PVCs, is also relatively rare in pediatric patients. Although there are multiple causes of ventricular tachycardia, it usually is a sign of serious cardiac dysfunction or disease. Rapid-rate ventricular tachycardia results in decreased cardiac output and cardiovascular instability. Treatment in symptomatic patients is synchronized cardioversion. Medical management with lidocaine or amiodarone may be appropriate in a conscious asymptomatic patient. Complete evaluation of the etiologic picture is necessary, including electrophysiologic study.
Firstdegree heart block is the presence of a prolonged PRinterval. It is asymptomatic and, when present in otherwisenormal children, requires no evaluation or treatment. Seconddegree heart block is when some, but not all, of the P waves are followed by a QRS complex. Mobitz type I (also known asWenckebach) is characterized by a progressive prolongationof the PR interval until a QRS complex is dropped. It is oftenseen during sleep, usually does not progress to other forms ofheart block, and does not require further evaluation or treatment in otherwise normal children. Mobitz type II is presentwhen the PR interval does not change, but a QRS is intermittently dropped. This form may progress to complete heart blockand may require pacemaker placement. Thirddegree heart block, whether congenital or acquired, is present when thereis no relationship between atrial and ventricular activity. Theventricular rate is much slower than the atrial rate. Congenital complete heart block is associated with maternal collagen vascular disease (such as systemic lupus erythematosus or Sjögrensyndrome) or congenital heart disease. The acquired form mostoften occurs after cardiac surgery but may be secondary toinfection, inflammation, or drugs.