Supraventricular Tachycardia

Synonym

Paroxysmal atrial tachycardia

Definition

                1. Supraventricular tachycardia (SVT) is defined as:

                a. Heart rate in infants and young children >220 bpm (range: 220 to 320 bpm; Fig. 5-10)

                b. Heart rate in older children >180 bpm (range: 180 to 250 bpm)

                2. SVT is the most common dysrhythmia seen in the pediatric age group.

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Figure 5-10. Supraventricular Tachycardia

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A ventricular rate of 250 bpm with a narrow QRS complex in a 12-day-old neonate who presented with poor feeding and irritability of several hours' duration. The patient had good capillary refill and peripheral perfusion with a BP of 104/73. The patient received one dose of IV adenosine followed by conversion to regular sinus rhythm.       

Etiology

                1. SVT is most commonly caused by a reentry mechanism involving atrioventricular [AV] nodal reentry, accessory pathways, or increased automaticity.

                2. SVT due to accessory pathway conduction (e.g., Wolff-Parkinson-White syndrome [WPW syndrome]) is the predominant mechanism in the fetus and young infant. AV nodal reentry typically appears in 5- to 10-year-old children, and is the predominant mechanism in adults.

                3. Primary atrial tachycardia (e.g., atrial flutter or fibrillation) accounts for 10 to 15% of SVT at all ages.

                4. Associated structural heart disease (e.g., Ebstein's anomaly, corrected transposition of the aorta) is present in about 20% of cases.

                5. Other etiologies include drugs (e.g., cold medications containing sympathomimetics), hyperthyroidism, myocarditis, cardiomyopathy, or infections.

Associated Clinical Features

                1. Usual presentation:

                a. Infants usually present with nonspecific symptoms of poor feeding, irritability, or restlessness.

                b. If SVT persists for many hours at rapid rates, signs of congestive heart failure (e.g., tachypnea, tachycardia, hepatomegaly) or cardiogenic shock/cardiovascular collapse (e.g., an acutely ill infant with prolonged capillary refill, thready pulses, poor tissue perfusion, ashen color, and metabolic acidosis) develop.

                c. About 20% of infants may be completely asymptomatic and SVT may be detected during a routine examination.

                d. Older children may present with pounding or racing heartbeat, dizziness, diaphoresis, or tiredness.

                e. Episodes of SVT are often paroxysmal; older children may give a history of episodes of a racing heartbeat that starts and stops suddenly.

                f. Chest pain is not a usual presenting symptom of SVT.

                2. Clinically the heart rate may be too rapid to count.

                3. Most common age at presentation:

                a. Most first episodes of childhood SVT occur in the first 2 months of life.

                b. About 60% of cases: infants <4 months of age

                c. About 80% of cases: infants <12 months of age

                4. Electrocardiography is required to confirm the diagnosis:

                a. P waves may not be visible (obscured by the ST segment).

                b. QRS complex

                1) Narrow QRS complex in 90% of cases

                2) Wide QRS complex in 10% of cases (aberrant SVT)

                c. With persistent tachycardia, ST- and T-wave changes consistent with myocardial ischemia may be seen.

                d. Features of WPW syndrome may be seen once the episode of SVT terminates, and may include a short PR interval, a delta wave (slow upstroke of QRS complex), and a wide QRS complex.

                5. A chest radiograph may show the presence of cardiomegaly, suggesting CHF or underlying structural heart disease.

Consultation

Cardiology consultation (once the patient is stabilized) for:

                1. Echocardiography in patents with a first episode of SVT (to rule out associated structural heart disease)

                2. Beginning chronic maintenance therapy (e.g., digoxin, propranolol, procainamide, or amiodarone) as indicated in patients with either a first episode or recurrent episodes of SVT

                3. Possible electrophysiology testing and radiofrequency catheter ablation for patients with refractory SVT, those requiring multiple medications, or those with undesirable side effects from medications

Emergency Department Treatment and Disposition

                1. Evaluation of the hemodynamic status and stabilization as indicated; high-flow oxygen, continuous cardiac, blood pressure, and pulse oximetry monitoring

                2. SVT without circulatory compromise (stable patient):

                a. Vagal maneuvers that heighten the vagal tone to the AV node

                1) Diving reflex: application of an ice bag to the face in infants or submersion of the face in ice cold water in older children (Caution:Application of ice to infants should be brief [10 to 20 seconds max], and a cloth or plastic barrier should be used to avoid the occurrence of fat necrosis. Avoid repeated applications of ice to the same location.)

                2) Valsalva maneuver: Ask the patient to strain as if attempting straining at stool.

                3) Unilateral carotid massage: Massage at the junction of the carotid artery and the mandible.

                4) Ocular pressure should not be used (due to the risk of retinal detachment).

                b. Adenosine (Box 5-22; Figs. 5-11 and 5-12)

                c. Verapamil

                1) Do not use in infants < 1 year of age (life-threatening side effects include profound bradycardia, hypotension, and cardiac arrest).

                2) Do not use in children with CHF, myocardial depression, or those receiving beta-blockers.

                3. SVT with circulatory compromise or severe CHF (unstable patient with shock, acidosis):

                a. Adenosine (Box 5-22) if immediate vascular access is available

                b. Synchronized cardioversion (synchronization of the delivered energy with the ECG reduces the possibility of inducing VF, which can occur if the energy is delivered during the relative refractory period of the ventricle)

                1) Consider sedation in older children (if the patient is conscious and time and clinical condition allow; however, sedation must not delay cardioversion).

                2) Initial dose: 0.5 to 1 joule/kg

                3) Double the dose if SVT persists.

                4) Reconsider the diagnosis of SVT if conversion to sinus rhythm does not occur; patient may actually have sinus tachycardia.

                4. Admit to the ICU to monitor for recurrences of SVT and for further management.

                a. Any patient presenting with hemodynamic instability

                b. Any patient with a first episode of SVT (e.g., for parental and patient education, and to begin maintenance therapy, especially in neonates and infants with possible recurrences of SVT)

                5. Patients known to have SVT can be discharged home once converted to sinus rhythm; make a follow-up appointment with the cardiologist or primary care physician.

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Figure 5-11. Supraventricular Tachycardia

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Following one dose of IV adenosine, an abrupt change from SVT to one premature ventricular contraction followed by sinus rhythm is seen.    

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Figure 5-12. Two-Hand/Two-Syringe Technique for Administration of Adenosine

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Because of its extremely short half-life, adenosine must be given as a rapid IV bolus (inject in 1 to 3 seconds to maximize the concentration that reaches the heart). While maintaining pressure on the plunger of the syringe containing the adenosine, simultaneously inject a rapid bolus of 3 to 5 mL of normal saline to accelerate delivery to the heart. Injection should be made close to the hub of the catheter, so that it is done closest to the patient. Intravenous tubing above the injection port should be clamped before the adenosine/normal saline push, and it should be unclamped after the injection.               

Clinical Pearls: Supraventricular Tachycardia

                1. SVT is the most common dysrhythmia seen in the pediatric age group.

                2. Aberrant SVT presents with a wide QRS complex and may resemble VT. If uncertain, all wide-complex tachycardias are assumed to be VT.

                3. A diagnosis of sepsis may be mistakenly made in an infant with SVT presenting with poor feeding, irritability, rapid breathing, or shock.

                4. Heart rates >220 bpm are highly unusual for ST and probably suggest SVT.

                5. Do not delay cardioversion in severely compromised patients while trying to establish vascular access.

                6. Do not prescribe sympathomimetics (common in over-the-counter decongestants) for the treatment of upper respiratory infections in children with SVT, and advise patients also to avoid caffeine.

Box 5-21. Differential Diagnosis: Sinus Tachycardia versus Supraventricular Tachycardia

Sinus Tachycardia             Supraventricular Tachycardia

History of volume loss (vomiting, diarrhea, blood loss), fever, hypoxia    History nonspecific (e.g., irritability, poor feeding, excessive crying)

Signs of dehydration or hypovolemic shock or sepsis (depending on underlying etiology)              Signs of cardiogenic shock (tachypnea, sweating, pallor, or hypothermia)

Rate greater than normal for age (usually <220 bpm)      Rate > 220 bpm in infants; rate >180 bpm in older children

Regular rhythm Usually regular rhythm (associated AV block extremely rare)

Beat-to-beat variation (e.g., HR decreases with sleep or when quiet)      No beat-to-beat variation; monotonous/fixed rate

Normal P-wave axis        P-wave axis usually abnormal

P wave may not be identifiable (with very high ventricular rate)                P wave may not be identifiable (with very high ventricular rate)

Some variation in RR interval may be present     Monotonous/fixed RR interval

Normal QRS duration     Normal QRS duration in >90% of cases

Heart rate slows gradually with treatment (e.g., O2 therapy for hypoxia or fluids for dehydration)

                Abrupt termination to sinus rhythm (either spontaneously or with treatment)

Normal P-QRS-T–wave sequence            

Box 5-22. Adenosine and Supraventricular Tachycardia

 Drug of choice in stable patients or acutely ill patients with readily available vascular access

 Relatively safe drug that can be given to infants and children of all ages, including full-term and preterm newborn infants

 May also be used in children with WPW syndrome or other AV bypass tracts

 After its administration:

   (1) It transiently depresses sinus and AV nodes, leading to slowed conduction and interruption of the reentry pathway

   (2) Be prepared to expect brief periods of sinus arrest (asystole).

   (3) Also be prepared to treat other hemodynamically compromising cardiac effects such as bradycardia, AV block, atrial fibrillation, atrial flutter, ventricular tachycardia, or ventricular fibrillation.

 Untoward effects are brief (ultra-short half-life [ < 10 seconds]):

   (1) Dyspnea, flushing, chest pain/discomfort, headache, episodes of apnea

   (2) Bronchospasm (asthma is not a contraindication to adenosine use; however, be prepared to treat immediate or delayed bronchospasm)

 Dose and route of administration:

   (1) Initial dose 0.1 to 0.3 mg/kg (maximum first dose: 6 mg)

   (2) If initial dose is unsuccessful, may double and repeat dose once (maximum second dose: 12 mg)

   (3) Maximum single dose: 12 mg

   (4) Use rapid IV bolus followed by normal saline flush (see two-hand technique, Fig. 5-12).

   (5) May be given intraosseously

   (6) Adolescents  50 kg: 6 mg rapid IV push; if no response after 1–2 min, give 12 mg rapid IV push. May repeat a second 12 mg dose after 1–2 min, if required.