Supraventricular tachycardia (SVT)

Any tachycardia originating from a focus that is above the ventricles can be termed “supraventricular tachycardia” or SVT. Although logically speaking, this should include sinus tachycardia (coming from the sinoatrial node, or the SA-node), the term SVT has been traditionally used while excluding sinus tachycardia. The reason is that sinus tachycardia should be considered physiological and serving a metabolically demanding need (such as fear, fever, pain, anxiety, heart failure, hyperthyroidism, intoxication, and other reasons for a normally elevated sympathetic tone), rather than pathological, as opposed to all other types of SVT. This is also the reason why SVT is typically faster than sinus tachycardia.

This exclusion leaves us with atrial tachycardia (a series of consecutive APCs), AV-nodal (also known as “nodal” or “junctional”) tachycardia, and even atrial fibrillation or atrial flutter. There are several types of SVT (Focal atrial tachycardia, Orthodromic atrioventricular re-entrant tachycardia, Antidromic atrioventricular re-entrant tachycardia, etc.), the definitions of which are beyond the scope of this text. Often such a tachycardia (atrial fibrillation or flutter are an exception) has a regular rhythm and its QRS complexes are narrow with a normal looking morphology, unless there is a concomitant intra-ventricular conduction anomaly or delay (see BBB). Depending on the heart rate, P-waves may or may not be visible, preceding each QRS complex or superimposed on (or “buried within”) the T-wave belonging to the preceding cardiac cycle. The presence of an SVT does not mean that other types of arrhythmia or a concomitant conduction anomaly cannot coexist.

Examples of SVT are depicted in the following cases:

HR = 122 bpm (sinus rhythm), 240-250 bmp (SVT), P = 40 ms & 0.25 mv, PR = 110ms, QRS = 60 ms, R = 1.05 mV, QT = 180 ms | view the full report

HR = 170-204 bpm, P = 45 ms,  PR = 90 ms, QRS = 65 ms, R = 1.85 mV, QT = 180 ms | view the full report

HR = 300 bpm, QRS = 50 ms, R = 2.0 mV, QT = 130-140 ms | view the full report