ESSENTIALS OF DIAGNOSIS
Rapid, regular tachycardia most commonly seen in young adults and characterized by abrupt onset and offset.
QRS duration narrow (less than 120 msec) except in the presence of bundle branch block or accessory pathway.
Often responsive to vagal maneuvers, AV nodal blockers, or adenosine. Cardioversion rarely required.
PSVT is an intermittent arrhythmia that is characterized by a sudden onset and offset and a regular ventricular response. Episodes may last from a few seconds to several hours or longer. PSVT often occurs in patients without structural heart disease. The most common mechanism for PSVT is reentry, which may be initiated or terminated by a fortuitously timed atrial or ventricular premature beat. The reentrant circuit usually involves dual pathways (a slow and a fast pathway) within the AV node; this is referred to as AV nodal reentrant tachycardia (AVNRT) and accounts for 60% of cases of PSVT. Less commonly (30% of cases), reentry is due to an accessory pathway between the atria and ventricles, referred to as atrioventricular reciprocating tachycardia (AVRT). The pathophysiology and management of arrhythmias due to accessory pathways differ in important ways and are discussed separately below.
Symptoms of PSVT can be quite variable depending on the degree of heart rate elevation, resultant hypotension or the presence of other comorbidities. Symptoms may include palpitations, diaphoresis, dyspnea, dizziness, and mild chest pain (even in the absence of associated CHD). Syncope is rare.
Obtaining a 12-lead ECG when feasible is important to help determine the tachycardia mechanism. The QRS duration will be narrow (less than 120 ms) except in cases of PSVT with aberrant conduction (left bundle branch block, right bundle branch block, or antegrade conducting accessory pathway). The heart rate is regular and is usually 160–220 beats/min but may be greater than 250 beats/min. The P wave usually differs in contour from sinus beats and is often simultaneous with or just after the QRS complex.
In the absence of structural heart disease, serious effects are rare, and most episodes resolve spontaneously. Particular effort should be made to terminate the episode quickly if cardiac failure, syncope, or anginal pain develops or if there is underlying cardiac or (particularly) coronary disease. Because reentry is the most common mechanism for PSVT, effective therapy requires that conduction be interrupted at some point in the reentry circuit and the vast majority of these circuits involve the AV node.
A variety of maneuvers have been used to interrupt episodes, and patients may learn to perform these themselves. These maneuvers result in an acute increase in vagal tone and include the Valsalva maneuver, lowering the head between the knees, coughing, splashing ...