supraventricular tachycardia
“Supraventricular” simply means “above the ventricles.” Supraventricular tachycardia is an umbrella term for fast rhythms that originate in or above the AV node — in the atria or the junction between atria and ventricles — usually striking suddenly, racing along at 150 to 250 beats a minute, and stopping just as abruptly. Many people describe it as the heart switching into a sudden gallop and then snapping back to normal.
Most common SVTs depend on a tiny re-entry circuit, where an electrical impulse loops endlessly through two pathways near or around the AV node. The classic forms are AV nodal re-entrant tachycardia, which uses a fast and a slow pathway inside the node, and AV re-entrant tachycardia, which uses an extra accessory connection.
Although alarming and uncomfortable — with pounding, breathlessness or light-headedness — most SVT in an otherwise healthy heart is not life-threatening. Episodes can often be stopped with simple vagal manoeuvres or a rapid intravenous drug, and recurrent cases are frequently cured permanently by catheter ablation.
A young adult arrives with a sudden regular racing heartbeat of 190; bearing down hard against a closed throat slows the AV node and the rhythm abruptly returns to normal.
Re-entrant SVT often starts and stops abruptly and can respond to a vagal manoeuvre.
Vagal manoeuvres such as bearing down or carotid sinus massage briefly slow AV-node conduction and can terminate many re-entrant SVTs without any drug.