Overview
Definition:
Supraventricular tachycardia (SVT) in infants is a sustained heart rhythm with a ventricular rate typically exceeding 180-220 beats per minute, originating from above the ventricles
Vagal maneuvers are non-pharmacological techniques that stimulate the vagus nerve to slow heart rate.
Epidemiology:
SVT is the most common sustained tachyarrhythmia in infancy, with an incidence of 1 in 2500 live births
It often presents within the first few months of life
Recurrence is common, and prompt recognition and management are crucial.
Clinical Significance:
Unrecognized or untreated SVT in infants can lead to hemodynamic instability, heart failure, profound irritability, feeding difficulties, and potentially cardiogenic shock
Effective management, including appropriate vagal maneuvers, is vital for infant well-being and reduces the need for immediate pharmacological intervention.
Clinical Presentation
Symptoms:
Sudden onset of rapid heart rate
Infant appears pale and irritable
Poor feeding
Tachypnea or difficulty breathing
Vomiting
Lethargy or unresponsiveness
In severe cases, signs of shock: cool extremities, decreased perfusion, hypotension.
Signs:
Heart rate > 180-220 bpm, often regular and narrow complex on palpation of pulse or auscultation
May have a short RP interval on ECG
Possible signs of poor perfusion: delayed capillary refill, mottled skin
Signs of heart failure: hepatomegaly, pulmonary rales.
Diagnostic Criteria:
Diagnosis is confirmed by electrocardiogram (ECG) demonstrating a narrow-complex tachycardia with a heart rate above established infant norms, usually with absent or inverted P waves in inferior leads
Differentiating between sinus tachycardia and SVT is critical.
Diagnostic Approach
History Taking:
Focus on the onset and duration of symptoms
Any prior episodes
Maternal history of arrhythmias
Family history of sudden cardiac death or arrhythmias
Recent febrile illness or dehydration.
Physical Examination:
Assess infant's general appearance, perfusion, and respiratory status
Palpate peripheral pulses for rate and regularity
Auscultate heart sounds, noting rate, rhythm, and presence of murmurs
Assess for hepatomegaly and lung auscultation findings.
Investigations:
A 12-lead ECG is paramount to confirm the diagnosis, determine the rhythm (e.g., AVNRT, AVRT), and assess hemodynamic stability
Echocardiography may be performed to evaluate for structural heart disease if the diagnosis is unclear or if there are signs of heart failure.
Differential Diagnosis:
Sinus tachycardia (due to fever, crying, dehydration, anxiety)
Other supraventricular arrhythmias like atrial flutter or fibrillation (rare in infants)
Ventricular tachycardia (very rare in infants without structural heart disease)
Sepsis.
Management
Initial Management:
Assess hemodynamic stability
If stable, attempt vagal maneuvers first
If unstable, proceed to immediate synchronized cardioversion
Ensure IV access and resuscitation equipment are readily available.
Vagal Maneuvers:
Techniques include: ice pack to the face (occlusion of nares and mouth, but allow breathing)
Stimulating the pharynx or posterior palate with a tongue depressor or cotton swab
Valsalva maneuver (if age-appropriate and feasible, typically older infants)
**Crucially, these must be performed carefully in infants to avoid hypoxia.**
Pharmacological Management:
If vagal maneuvers fail or are not feasible: Adenosine is the first-line drug
Administered as a rapid IV bolus (0.1 mg/kg, then 0.2 mg/kg if needed) followed by a saline flush
Amiodarone or procainamide may be used if adenosine is ineffective or contraindicated.
Supportive Care:
Continuous cardiac monitoring
Oxygen supplementation if hypoxic
Management of heart failure if present
Close observation for recurrence or complications
Hydration and nutritional support.
Complications
Early Complications:
Refractory SVT despite interventions
Hemodynamic collapse leading to shock
Paradoxical bradycardia with AV nodal blocking agents
Hypotension from cardioversion.
Late Complications:
Recurrence of SVT episodes
Development of heart failure
Potential for increased risk of arrhythmias later in life, especially if underlying structural heart disease exists.
Prevention Strategies:
For recurrent SVT, long-term antiarrhythmic therapy (e.g., flecainide, sotalol) may be initiated
Catheter ablation is an option for refractory or frequent symptomatic episodes, especially in older infants and children
Education of parents on recognizing symptoms and when to seek medical attention.
Prognosis
Factors Affecting Prognosis:
Hemodynamic stability at presentation
Presence of underlying structural heart disease
Effectiveness of initial management
Frequency and duration of SVT episodes.
Outcomes:
Most infants with SVT respond well to initial management with vagal maneuvers or adenosine
Those with structurally normal hearts have an excellent prognosis after successful treatment and often do not require long-term therapy or ablation.
Follow Up:
Regular cardiology follow-up is recommended to monitor for recurrence, assess growth and development, and re-evaluate the need for ongoing treatment or ablation
Parents should be educated on symptom recognition and emergency contact protocols.
Key Points
Exam Focus:
Vagal maneuvers are the first-line treatment for stable infants with SVT
Adenosine is the drug of choice if maneuvers fail
Differentiate SVT from sinus tachycardia
ECG findings are diagnostic
Unstable infants require immediate cardioversion.
Clinical Pearls:
Be quick and decisive with interventions
Ice pack to the face is often effective but monitor for hypoxia
Adenosine has a very short half-life, hence the rapid flush is crucial
Always have resuscitation equipment ready.
Common Mistakes:
Delaying intervention in unstable infants
Incorrectly administering adenosine (too slow, wrong dose)
Misinterpreting sinus tachycardia as SVT
Forgetting to consider underlying causes like sepsis.