Supraventricular Tachycardia (SVT)
SVT is a broad term for a number of tachyarrhythmias that originate above the ventricular electrical conduction system (purkinje fibers).
Classic Paroxysmal SVT has a narrow QRS complex & has a very regular rhythm. Inverted P waves are sometimes seen after the QRS complex. These are called retrograde p waves
The heart fills during diastole, and diastole is normally 2/3 the cardiac cycle. A rapid heart rate will significantly reduce the time which the ventricles have to fill. The reduced filling time results in a smaller amount of blood ejected from the heart during systole. The end result is a drop in cardiac output & hypotension.
With the drop in cardiac output, a patient may experience the following symptoms. These symptoms occur more frequently with a heart rate >150 beats per minute:
- Shortness of air (S)
- Palpitation feeling in chest (S)
- Ongoing chest pain (U)
- Dizziness (S)
- Rapid breathing (S)
- Loss of consciousness (U)
- Numbness of body parts (S)
The pathway of choice for SVT in the tachycardia algorithm is based on whether the patient is stable or unstable. The symptoms listed above that would indicate the patient is unstable are noted with the letter (U). Stable but serious symptoms are indicated with the letter (S).
Unstable patients with SVT and a pulse are always treated with cardioversion. The appropriate voltage for cardioverting SVT is 50-100 J. This is what AHA recommends and also SVT converts quite readily with 50-100 J.