- Clinical science
Paroxysmal supraventricular tachycardia (PSVT) is a type of arrhythmia arising from a defect in atrioventricular conduction, which causes the heart to sporadically beat faster. There are different forms of PSVT, including atrioventricular nodal reentrant tachycardia (AVNRT; about two-thirds of cases), atrioventricular reentrant (or reciprocating) tachycardia (AVRT), and atrial tachycardias. In AVNRT, extra electrical conduction pathways (accessory pathways) within the AV node lead to non-extinguishable, circulating electrical impulses (reentrant circuits). AVRT, on the contrary, is caused by circular depolarizations that travel through ectopic connections between the atria and ventricles. PSVT is characterized by tachycardia attacks that may cause dizziness, dyspnea, chest pain or syncope, and are usually self-limiting. Diagnostic steps for any type of PSVT include obtaining the patient history and a 12-lead ECG, which typically shows tachycardia and narrow QRS complexes. Because most tachycardia attacks subside before an ECG is conducted, continuous recording with a Holter monitor is often needed to confirm the diagnosis. In some cases, invasive electrophysiological studies may be indicated. Patients with a congenital condition known as Wolff-Parkinson-White (WPW) syndrome commonly exhibit AVRT because of the presence of an accessory pathway known as the bundle of Kent. This pathway bypasses the AV node and transmits the sinus impulse directly to the ventricles, resulting in a premature depolarization (pre-excitation) that appears as a delta wave on ECG. Management of PSVT should be tailored to the individual patient: hemodynamically unstable patients should undergo urgent cardioversion, whereas patients who are hemodynamically stable may benefit from vagal maneuvers, e.g., carotid massage. Pharmacologic therapy is indicated if the sinus rhythm cannot be restored by vagal maneuvers. The appropriate drug depends on the conduction pathway in the heart as revealed by ECG findings. Catheter ablation may be performed as a definitive treatment.
- Atrioventricular nodal reentrant tachycardia (AVNRT): tachycardia caused by a dysfunctional AV node that contains two electrical pathways
Atrioventricular reciprocating tachycardia (AVRT): tachycardia caused by an accessory pathway between the atria and ventricles
Wolff-Parkinson-White syndrome (WPW): A congenital condition characterized by intermittent tachycardias and signs of ventricular pre-excitation on ECG, which both arise from an accessory pathway known as the “bundle of Kent”
- The bundle of Kent connects the atria and ventricles, bypassing the AV node and leading to a pre-excitation of the ventricles.
- Multiple pathways are present in up 13% of patients with WPW
- Up to one-third of patients may develop paroxysmal atrial fibrillation.
- May result in supraventricular tachycardia due to a reentry circuit
- About 3% of patients have familial WPW, which has an autosomal-dominant mode of inheritance.
- Bidirectional conduction, either anterograde or retrograde (60–75%)
- Anterograde conduction (5–27%)
- Retrograde conduction (17–37%) → "concealed" delta wave
- Wolff-Parkinson-White syndrome (WPW): A congenital condition characterized by intermittent tachycardias and signs of ventricular pre-excitation on ECG, which both arise from an accessory pathway known as the “bundle of Kent”
Atrial tachycardia (AT): The atria respond to impulses from an atrial pacemaker outside of the SA node.
- There are two types:
- Atrial tachycardia is responsible for 10% of sustained PSVT.
- Can be caused by increased automaticity, triggered activity, or reentry
- May occur in patients with or without underlying heart disease.
- A common cause of AT includes digoxin poisoning which typically presents with concomitant AV block.
- Atrial fibrillation and atrial flutter: These conditions are types of supraventricular tachycardias, but are usually considered separately (see ).
- Permanent junctional reciprocating tachycardia (PJRT)
- The AV node contains two electrical pathways: one fast and one slow → the electrical impulse circles around the AV node within both pathways → continuous circuit that conducts impulses to the ventricles → tachycardia
- Approx. 90% of cases are due to anterograde conduction across the slow-conducting pathway and retrograde in the fast pathway (although the reverse is possible)
- There are two types of atrioventricular reentrant tachycardia. The direction of the reciprocating impulse helps distinguish between the two:
- Orthodromic AVRT: most common (90–95%) → narrow QRS complex
- Antidromic AVRT: least common (5–10%) → delta wave
Do not confuse atrioventricular reentrant (or reciprocating) tachycardia (AVRT) with atrioventricular nodal reentrant tachycardia (AVNRT)! AVRT is caused by an accessory pathway between the atrium and ventricle, while in cases of AVNRT, there are two functional pathways present within the AV node!
- Supraventricular: narrow QRS complex (< 120 ms)
- AVNRT: : no P waves or atrial activity
- AVRT: P wave in the ST segment
- AT, atypical AVNRT or junctional reciprocating tachycardia : RP interval longer than PR interval
- ECG may be normal
- During tachycardia:
- Orthodromic AVRT:
- Shortened PR interval
= slurred upstroke in QRS complex due to pre-excitation → wide QRS complex
- This feature of pre-excitation can not be observed during tachycardia or in a patient with "concealed pathway" (retrograde conduction)
- Commonly found on ECG in WPW
- Not visible during tachycardia or in patients with a concealed pathway (retrograde conduction)
- Delta wave positive in lead V1 and negative in leads I, aVL (left-sided accessory pathway)
- Delta wave negative in lead V1 and positive in leads I, aVL (right-sided accessory pathway)
Steps for identifying underlying causes
- Laboratory tests
- A catheter is inserted into a large vein (typically the femoral) and guided to the heart
- Wire electrodes are inserted that measure the heart's electrical activity
- Intracardiac recordings help identify accessory pathways and reentry circuits
- Generally conducted in combination with radiofrequency catheter ablation of accessory pathways
Hemodynamically unstable patient
- Cardioversion: fastest and most effective treatment of supraventricular tachycardia
Hemodynamically stable patient
- Goal: re-establish and maintain sinus rhythm
- Most asymptomatic patients do not require medical intervention, so observation is sufficient
Acute Management of PSVT
Vagal maneuvers: first step in acute management
Carotid sinus massage: pressure must be applied at the level of the carotid bifurcation unilaterally for 5–10 seconds at most
- Carotid sinus massage stimulates the baroreceptors → stimulates CN IX (specifically the branch of the glossopharyngeal nerve to the carotid sinus) → nerve impulse transmission to the medulla (nucleus tractus solitarius) → efferent signals from the medulla to the myocardium via the vagus nerve (parasympathetic supply) → ↓ AVN conduction, ↓ heart rate, ↓ contractility, and vasodilation (↓ blood pressure) → termination of arrhythmia
- glottis. : Following deep inspiration, the patient is told to perform an abdominal press and forcefully exhale against a closed
- Diving reflex: immersion of head in ice cold water
- Oculocardiac reflex: Compression is applied to the eyeball for at least one minute. This reflex may induce vomiting in patients and is suspected to be the cause of postoperative emesis after eye surgery. It is often not recommended because of it has been associated with retinal injury.
- Carotid sinus massage: pressure must be applied at the level of the carotid bifurcation unilaterally for 5–10 seconds at most
Medical therapy: if vagal maneuvers have failed
- AVNRT and orthodromic AVRT:
For antidromic AVRT: procainamide
- AV nodal blocking agents are contraindicated!
For WPW patients with AF: generally rhythm control (e.g., procainamide)
- AV nodal blocking agents are contraindicated!
AV nodal blocking agents (i.e., adenosine, verapamil, beta-blockers, digoxin, amiodarone) are contraindicated in patients with signs of preexcited tachycardia on ECG (e.g., antidromic AVRT; AF in WPW patient)!
- ECG should be recorded during acute management to identify and treat other arrhythmias if the treatment was unsuccessful
- A defibrillator should be ready in case new dysrhythmias emerge (especially for AF)
Administration of adenosine and calcium channel blockers together may potentiate a bradycardic or hypotensive response!
Long-term management of PSVT
- For the management of well-tolerated, infrequent episodes, the patient may be instructed to perform vagal maneuvers
Catheter radiofrequency ablation
- First-line therapy (curative) in AVNRT, AVRT, or drug refractory AT
- Indicated especially for:
- Symptomatic patients with concomitant structural heart disease
- Symptomatic patients who want to avoid long-term drug therapy (especially younger patients)
- Asymptomatic patients with special lifestyle considerations (e.g., pilots)
- Medical therapy (second line)