Chapter e1: Arrhythmias

DISEASE/CONDITION(S)

Irregular rhythms, tachycardias, bradycardias.

GUIDELINE OBJECTIVE(S)

Review diagnostic strategies and recommendations for management of common neonatal arrhythmias.

BRIEF BACKGROUND

Arrhythmias affect patients of all ages, from fetal life through adulthood. In normal infants, estimates of arrhythmia prevalence range from 0.75% to 14%. A correct diagnosis is essential for appropriate management and prognosis. Most arrhythmias diagnosed in infancy are benign and resolve either spontaneously or following a short course of pharmacotherapy. Supraventricular tachycardia (SVT) is the most common type of tachycardia, occurring in 1/250 infants, and 60% of children diagnosed with SVT develop their first episode before the age of 1 year. Neonatologists thus frequently diagnose and manage SVT. While bradycardias account for only 5% of arrhythmias in infants, their occurrence in infants can be life-threatening. Lastly, disorders of atrioventricular conduction may manifest in utero, and their complete diagnosis and initial management often occurs in the neonatal intensive care unit.

MAJOR RECOMMENDATIONS

1. Arrhythmias in the neonatal intensive care unit should be diagnosed using a 12- or 15-lead surface ECG, together with a rhythm strip or heart rate monitoring as needed. Close attention should be paid to appropriate lead placement.

2. If possible, treatment decisions should be made after a specific arrhythmia diagnosis has been made.

3. In the intensive care setting, arrhythmia treatment should not be delayed if the infant is unstable while a specific diagnosis is being made.

4. Not all forms of arrhythmias in infants require treatment.

5. Hemodynamic stability should be assessed repeatedly in infants diagnosed with arrhythmias.

6. Secondary causes of arrhythmias should be investigated, including cardiovascular and other diseases.

PRACTICE OPTIONS

The diagnosis and management of arrhythmias should occur in a controlled and monitored environment. Infants should undergo heart rate and rhythm, pulse oximetry, and blood pressure monitoring. If necessary, restoration of airway, breathing, and circulation should occur per resuscitation guidelines. Sedation and analgesia may be valuable for several diagnostic and therapeutic interventions including temporary pacing and cardioversion. However, while efforts should be made to provide appropriate levels of sedation and analgesia whenever possible, these efforts should not delay arrhythmia interventions in states of severe circulatory impairment.

At any time during the diagnosis and treatment of arrhythmias, consultation with a pediatric cardiologist should be considered, and the need for consultation should be frequently re-evaluated.

Practice Option #1: Diagnosis of Arrhythmias

Premature Contractions

Premature contractions (also known as premature beats, ectopic beats, or extrasystoles) are contractions occurring earlier than expected in the cardiac cycle. Premature beats can originate in the atria, the atrioventricular junction, or the ventricles.

Premature Atrial Contractions (PACs)

1. A QRS complex appears prematurely.

2. The p-wave morphology differs from the regular sinus rhythm (p-wave can still be upright in lead II if PAC originates from high in the right atrium).

3. The compensatory pause is incomplete: the length of two cycles, including one premature beat, is less than the length of two normal cycles.

Premature Ventricular Contractions (PVCs)

1. A differently shaped, often bizarre appearing QRS complex occurs prematurely.

2. The associated t-wave typically points in the opposite direction.

3. A full compensatory pause occurs: the length of two cycles, including one premature beat, is equal to the length of two normal cycles. The full compensatory pause occurs because the sinus node is not prematurely discharged by the PVC. However, if the PVC is conducted retrograde to the atria, the impulse may discharge the sinus node, producing an incomplete compensatory pause.

Nodal Premature Beats

1. The p-wave may be absent or inverted p-waves may follow the QRS complex.

2. The QRS complex is usually normal in duration and configuration.

3. The compensatory pause may be complete or incomplete.

Tachycardia

An area of the heart that depolarizes faster than the expected range for age for at least three consecutive beats. A ventricular rate >200 beats/minute in infants is usually considered tachycardia. Diagnosis is most readily and accurately accomplished by following a structured algorithm (Figure 1).

Bradycardia

An area of the heart that depolarizes slower than the expected range for age for at least three consecutive beats. In infants, a ventricular rate <100 beats/minute in infants is usually considered bradycardia.

1. A:V ratio 1:1 with normal PR interval and atrially derived rhythm:sinus node dysfunction

2. Prolonged PR interval: first-degree atrioventricular block

3. PR interval prolonging from beat to beat culminating in dropped beat: Mobitz type 1 second-degree AV block

4. No PR prolongation but intermittent dropping of QRS complexes: Mobitz type 2 second-degree AV block

5. Atrioventricular dissociation with A:V ratio >1: third-degree AV block

Practice Option #2: Treatment of Arrhythmias

1. Intensive care management of premature contractions

   1. Premature atrial contractions

      1. Usually no hemodynamic significance, and do not require treatment

      2. Consider treatment of underlying cause, if possible

   2. Premature ventricular contractions

      1. Occasional PVCs are benign

      2. PVCs are significant if:

         1. Associated with congenital heart disease

         2. Multiform or occur in couplets

         3. Associated with hemodynamic symptoms

         4. Incessant

      3. Treatment options for significant PVCs include:

         1. Propranolol 2–4 mg/kg/day divided q6h or q8

         2. Atenolol 1–2 mg/kg/day divided q12h or q24h

2. Intensive care management of bradycardia

   1. Immediate measures should be taken in infants who are hemodynamically unstable, in heart failure, or who develop a ventricular escape rhythm

      1. Discontinue medications that may contribute to bradycardia

      2. Atropine 0.02 mg/kg IV bolus via central (preferred) or peripheral IV

      3. Isoproterenol 0.1–2 µg/kg/min IV infusion via central (preferred) or peripheral IV

      4. Temporary pacing using transcutaneous, esophageal, or surgically placed (epicardial) pacing leads

   2. In infants who are hemodynamically stable

      1. Discontinue medications that may contribute to bradycardia

      2. Prepare for temporary pacing if becomes necessary

   3. Consider surgical pacemaker placement for the following scenarios

      1. Congenital third-degree AV-block with wide QRS escape rhythm OR ventricular dysfunction (Class I level B)

      2. Congenital third-degree AV-block with a ventricular rate <50–55 beats/minute (Class I level B/C)

      3. Congenital third-degree AV-block in infant with congenital heart disease and ventricular rate <70 beats/minute (Class I level B/C)

3. Intensive care management of narrow complex tachycardia

   1. Immediate measures should be taken in infants who are hemodynamically unstable

      1. Synchronized cardioversion

   2. In infants who are hemodynamically stable

      1. Vagal maneuvers may be attempted, but pharmacologic therapy is preferred

      2. Several pharmacologic alternatives are available (Table 1)

      3. Catheter-based ablation has been successful, but is reserved for the most complex and refractory cases

4. Intensive care management of wide complex tachycardia

   1. Immediate measures should be taken in infants who are hemodynamically unstable

      1. Electrical cardioversion (2 J/kg), repeat if necessary or defibrillation (2–4 J/kg)

      2. Lidocaine 1 mg/kg IV bolus, if necessary may repeat twice, then infusion at 20–50 µg/kg/min

      3. Amiodarone 5 mg/kg over 20–45 min

      4. Correct electrolyte abnormalities including acidosis, hypoxemia, and hypoglycemia

   2. For infants with prolonged QTc interval during sinus rhythm who develop torsades de pointe tachycardia

      1. Defibrillation

      2. Magnesium sulfate: 15–30 mg/kg followed by infusion of 15 mg/kg/min

      3. Correct electrolytes, including hypokalemia

      4. Temporary pacing or isoproterenol may be necessary if patient is bradycardic, including in the period after cardioversion

5. Secondary prophylaxis for narrow complex tachycardia

   1. Secondary prophylaxis is often used to prevent SVT recurrence after initial episode, though its use remains controversial

   2. No randomized controlled trials have demonstrated the efficacy of one drug over another

   3. Evidence from retrospective studies suggests similar efficacy between both propranolol and digoxin

   4. Options for secondary prophylaxis of SVT include

      1. Propranolol: 2–4 mg/kg/day divided q6 hours or q8 hours PO

      2. Digoxin (Table 2)

DESCRIPTION OF IMPLEMENTATION STRATEGY

Attempt to make a diagnosis of type of arrhythmia prior to initiating therapy, unless infant is unstable; after diagnosis is made, select antiarrhythmic therapy based on diagnosis and infant characteristics.

Arrhythmias occur frequently in the neonatal intensive care unit. While most arrhythmias diagnosed in infants are benign, infants suffering from certain arrhythmias may develop significant hemodynamic compromise necessitating immediate intervention. The risk of hemodynamic compromise varies by type of arrhythmia, and not all forms require treatment. Despite the prevalence of arrhythmias in infants, no successful randomized controlled trials of arrhythmia therapy have been conducted in infants. Further studies are needed to identify the best therapies for arrhythmias in infants.