Paroxysmal Supraventricular Tachycardia Information
This is the commonest paroxysmal tachycardia and often occurs in patients without structural heart disease. Attacks begin and end abruptly and may last a few seconds to several hours or longer. The heart rate may be 140–240 beats/min (usually 160–220 beats/min) and is perfectly regular (despite exercise or change in position). The P wave usually differs in contour from sinus beats. Patients may be asymptomatic except for awareness of rapid heart action, but some experience mild chest pain or shortness of breath, especially when episodes are prolonged, even in the absence of associated cardiac abnormalities. Paroxysmal supraventricular tachycardia may result from digitalis toxicity and then is commonly associated with atrioventricular block.
Paroxysmal Supraventricular Tachycardia Information
The most common mechanism for paroxysmal supraventricular tachycardia is reentry, which may be initiated or terminated by a fortuitously timed atrial or ventricular premature beat. The reentry circuit most commonly involves dual pathways (a slow and a fast pathway) within the atrioventricular (AV) node. This is referred to as AV nodal reentry tachycardia (AVNRT). Less commonly, reentry is due to an accessory pathway between the atria and ventricles (AVRT). Approximately one-third of patients with supraventricular tachycardia have aberrant pathways to the ventricles. The pathophysiology and management of arrhythmias due to accessory pathways differs in important ways and are discussed separately below.
Treatment of the Acute Attack of Paroxysmal Supraventricular Tachycardia
In the absence of heart disease, serious effects are rare, and most attacks break spontaneously. Particular effort should be made to terminate the attack 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 paroxysmal atrial tachycardia, effective therapy requires that conduction be interrupted at some point in the reentry circuit.
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