Types of Supraventricular Tachycardia

AVNRT

The incidence of AVNRT in women is twice that in men. ⁷ It is correlated with lower estrogen levels and higher progesterone levels, and is therefore more common during the luteal phase of the menstrual cycle and less common during pregnancy. ⁸ AVNRT involves a pattern of reentry in persons who have two pathways in their atrioventricular (AV) node, one slow and one fast. ^{9– 11} These pathways create a continuous and self-propagating circuit with a rapid and regular ventricular response. The impulse exits the AV node in a retrograde manner (backward from the AV node to the atrium) and in an anterograde manner (forward from the AV node to the ventricle), simultaneously causing depolarization of the atrium and ventricle; this means P waves are usually hidden in the QRS complex or are visible early after the QRS complex on electrocardiography (ECG). ¹²

AVRT

The second most common type of SVT is AVRT. There is a progressive decline in the proportion of SVT caused by AVRT as age increases, from 60% in the first decade of life to 9% after 70 years of age. ⁴ Patients with AVRT have a bypass pathway that bridges the atrium and ventricle, creating an accessory track that can conduct impulses in an anterograde or retrograde manner and establish a reentry circuit. Anterograde conduction down an accessory pathway may reach the ventricle before the impulse through the AV node, producing preexcitation of a portion of the ventricle, which creates a slurred upstroke at the start of the QRS complex (delta wave) on ECG ( Figure 2). Patients with a delta wave and tachycardia have Wolff-Parkinson-White syndrome. The delta wave may be visible on ECG, although this depends on the location of the pathway because concealed accessory pathways do not show delta waves. AVRT can be present without the Wolff-Parkinson-White syndrome pattern when the pathway is retrograde and does not create a delta wave.

ATRIAL TACHYCARDIA

In contrast to AVNRT and AVRT, atrial tachycardia does not involve reentry through the AV node or ventricle. It is caused by a focal area of automaticity in the atrium. Atrial tissue adjacent to the crista terminalis in the right atrium or the ostia of the pulmonary veins in the left atrium is particularly susceptible to the development of automaticity. ¹⁴ P waves are seen before the QRS complexes, although they can be hidden in the T wave with tachycardia.

Evaluation

CLINICAL HISTORY

Most patients with SVT do not have known heart disease and may present with episodic tachycardia, palpitations, anxiety, light-headedness, dyspnea, fatigue, or pulsations in the neck. Because the occurrences are usually episodic, physical examination findings may be normal, and symptoms may be misdiagnosed as anxiety or panic attacks, especially in women. ¹⁵

The history helps identify the likely etiology and should include whether symptoms begin gradually or suddenly (eTable A). SVT tends to start and stop quickly, whereas sinus tachycardia has a gradual onset and resolution. The patient should be asked about precipitating factors, such as caffeine or other stimulant use, stress, and exercise. Onset with activity or a history of cardiac disease suggests a ventricular origin to the tachycardia rather than SVT, and these patients should be evaluated for underlying heart disease (coronary artery disease and structural heart disease).

DIAGNOSTIC TESTING

Because of the paroxysmal nature of SVT, ECG findings may be normal, and further assessment should include a 24- or 48-hour evaluation with a Holter monitor or, if the symptoms are infrequent, an event monitor. Initial blood work should include thyroid-stimulating hormone level, complete blood count, and basic metabolic panel, with consideration of B-type natriuretic peptide and cardiac enzyme measurements in patients with known or suspected heart disease. eTable B summarizes the physical examination and diagnostic workup. Table 1 lists indications for a cardiologist consultation. ^{11, 16}

Management

SHORT-TERM OR URGENT TREATMENT

If nonpharmacologic maneuvers are ineffective, pharmacotherapy is the next line of treatment ( Tables 3 ^{17, 18} and 4 ²³ ). Because of its quick onset, high effectiveness and short half-life (about 10 seconds), adenosine is recommended as the first-line agent. ¹⁷ Nondihydropyridine calcium channel blockers, such as verapamil and diltiazem, and beta blockers, such as metoprolol, can achieve a longer-lasting AV nodal block compared with adenosine and can be used acutely. Verapamil in particular is as effective as adenosine (approximately 90% effective) in terminating node-dependent SVT. Adenosine has a higher rate of minor adverse effects, and verapamil has a higher rate of hypotension; however, both agents are safe and effective, and one agent can be used if the other one is ineffective. ²⁴ Because these medications may excite atrial or ventricular tissue and cause atrial fibrillation, bradycardia, or rarely nonsustained ventricular tachycardia, a cardiac monitor should be used and a defibrillator available when the medications are administered. ²⁵

Because atrial tachycardia is not dependent on the AV node, these treatments do not terminate this arrhythmia but can be diagnostic by slowing the rate, allowing for better exposure of atrial activity on the ECG.

If the patient is clinically unstable (e.g., altered mental status, chest pain, acute heart failure, hypotension, shock), immediate direct-current cardioversion is indicated. ¹⁷ However, even in these cases, the high effectiveness and fast onset of adenosine may merit its use as first-line treatment, with cardioversion used only if adenosine is ineffective. ²⁷

Wide QRS Complex. Because SVT can occasionally cause a wide QRS complex, it can be difficult to distinguish from ventricular tachycardia. In the acute setting, ventricular tachycardia should be assumed, particularly in patients who are hemodynamically unstable. Adenosine is safe and effective for diagnosis and treatment in undifferentiated regular wide complex tachycardia. ²⁷ If the underlying rhythm is SVT with aberrancy, it will be slowed or converted to sinus rhythm. If it is ventricular tachycardia, the rhythm will likely be unaffected, and procainamide, amiodarone, or sotalol should be administered. ¹⁷ If the patient remains unstable, cardioversion is indicated.

The Brugada criteria ( Table 5) can help distinguish between SVT with aberrancy and ventricular tachycardia, with a sensitivity and specificity of more than 96%. ²⁸

LONG-TERM MANAGEMENT

Pharmacologic Treatment. If the SVT episodes are infrequent but last more than one hour, a “pill-in-the-pocket” approach may be effective. Patients self-administer as-needed doses of nondihydropyridine calcium channel blockers, beta blockers, or antiarrhythmics ( Tables 3 ^{17, 18} and 4 ²³ ); effectiveness of this treatment method ranges from 30% to 60%. ²⁹ One study showed that using diltiazem (120 mg) plus propranolol (80 mg) or flecainide (3 mg per kg) alone as episodic treatment significantly reduced emergency department visits. ³⁰

For patients with more frequent episodes, limited data suggest that nondihydropyridine calcium channel blockers or beta blockers can modify conduction across the AV node and reduce the number and duration of AVNRT episodes. ¹⁸ The class Ic antiarrhythmics flecainide and propafenone (Rythmol) depress conduction across an accessory pathway (AVRT) and suppress episodes in most patients. These same medications can be attempted in patients with atrial tachycardia. The class Ia medications quinidine, procainamide, and disopyramide (Norpace) are less commonly used because of their modest effectiveness, and adverse and proarrhythmic effects. The class III medications amiodarone, sotalol, and dofetilide (Tikosyn) are effective, but they can have adverse effects and should be administered in consultation with a cardiologist.

Catheter Ablation. Catheter ablation is an effective first-line treatment option for many patients with AVRT or AVNRT. ^{18, 31, 32} Atrial tachycardia can be treated with catheter ablation if there is a focus. In general, ablation is offered to patients with recurrent SVT despite pharmacologic treatment or to those who do not want to take medications long-term. Catheter ablation is the standard of care for older children with symptomatic SVT, although pharmacologic therapy remains the treatment of choice for newborns and infants. ⁶

Catheters are inserted via a femoral vessel and use energy to ablate a focal region critical to the arrhythmia. Ablation has a success rate of 95%, with a recurrence rate of less than 5% and a rate of inadvertent heart block of less than 1%. ^{33– 36} Although relatively uncommon, heart block is a serious complication, particularly in young persons with SVT that is bothersome but not life-threatening. This has increased interest in alternatives that may have a better safety profile, such as cryoablation.

One study demonstrated high immediate ablation success rates of 96.8% and 98.4% for cryoablation and radiofrequency catheter ablation, respectively, but AVNRT recurrence was significantly more common in the cryoablation group (9.4% vs. 4.4%). Permanent AV block did not occur in the cryoablation group and occurred in 0.4% of the radiofrequency catheter ablation group. ³¹ Another study showed a 6% SVT recurrence rate after cryoablation. ³² Radiofrequency catheter ablation's lower recurrence rate makes it preferable to cryoablation in adults, but cryoablation's slightly lower incidence of postprocedure AV block may make it more desirable in younger patients. ³⁷ Other complications, such as femoral arteriovenous fistula and deep venous thrombosis, have been reported but are rare. ³⁸ Magnetic navigation systems for ablation are being developed to reduce radiation exposure, but effectiveness or superiority to current methods has not been established. ³⁹

Patients with Wolff-Parkinson-White syndrome cannot receive nodal-blocking medications in the long-term because of the risk of ventricular fibrillation; therefore, symptomatic patients should receive catheter ablation. ¹⁸ The best treatment approach for asymptomatic individuals is less clear given the low risk of arrhythmia and sudden death, which appeared comparable to the risk of ablation in a recent meta-analysis. ⁴⁰

Data Sources: A PubMed search was completed using the key terms supraventricular tachycardia, paroxysmal supraventricular tachycardia, atrial premature complexes, Valsalva maneuver, and Wolff-Parkinson-White syndrome. This search included meta-analyses, clinical trials, and reviews, limited to English-language articles about human participants. Also searched were the Cochrane database, National Guideline Clearinghouse, Essential Evidence Plus, and UpToDate. Search dates: October 2014 to January and August 2015.

Figures 2 and 3 courtesy of Paul Mounsey, MD.