Supraventricular Tachycardia (SVT) is a broad term for a number of tachyarrhythmias that originate above the ventricular electrical conduction system (purkinje fibers).
In infants and children, the most common form of SVT (re-entrant SVT) is caused by a reentry mechanism through a bypass pathway between atria and ventricles in addition to the AV node. This form of SVT makes up about 90% of SVT cases in infants and children.
In infants, the heart rate will typically be greater than or equal to 220 beats per minute,
In children, the heart rate will typically be greater than or equal to 180 beats per minute.
If no underlying health conditions exist, infants and children can tolerate SVT quite well, and as a result, it can go undetected until cardiovascular compromise becomes apparent.
The heart fills during diastole, and diastole is normally 2/3 the cardiac cycle. The rapid heart rate associated with SVT can 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. Ultimately, the end result is a drop in cardiac output & hypotension.
With the drop in cardiac output, an infant or child may experience the following signs and symptoms. These symptoms occur more frequently with a heart rate >150 beats per minute:
- Shortness of air
- Palpitation feeling in chest
- Ongoing chest pain
- Rapid breathing
- Altered or complete loss of consciousness
- Other signs of shock
Characteristics of the ECG for SVT include:
The ECG produced by SVT has specific characteristics that when recognized will help you make the determination that a rhythm truly is SVT. These characteristics are listed below.
- Heart Rate: No beat to beat variability with stress or activity
- P waves: Usually absent but may be abnormal.
- R to R interval: usually constant
- QRS complex: Usually narrow. May be wide of an aberrancy is present, but this is rare.
Another key indicator that distinguishes SVT is its very abrupt onset as compared with ST which usually has a more gradual onset and will be associated with some factor like fever, fluid loss, anxiety, etc.
Once SVT is recognized, it should be managed with one of the tachycardia algorithms.
For the management of SVT use these three questions to determine which tachycardia algorithm to use. These questions will also direct the management within the algorithm:
- Is a pulse present?
- Is perfusion adequate?
- Is the QRS complex normal/narrow or wide? (narrow complex QRS (≤ 0.09 sec) or wide complex QRS (>0.09)?
Perfusion status is the decision point for determining which tachycardia algorithm is used.