Tachycardia is defined as a heart rate greater than what is considered normal for a child’s age. Like bradycardia, tachycardia can be life threatening if it compromises the heart’s ability to perfuse effectively. When the heart beats too quickly, there is a shortened relaxation phase. This causes two main problems: 1) the ventricles are unable to fill completely, so cardiac output is lowered and 2) the coronary arteries receive less blood, so supply to the heart is decreased.
There are several kinds of tachycardia and they can be difficult to differentiate in children on ECG due to the elevated heart rate.
- Sinus tachycardia
- Normal rhythm with fast rate, likely non-dangerous, commonly occurring during stress or fever
- Supraventricular tachycardia
- Rhythm starts above the ventricles
- Atrial fibrillation
- Causes an “irregularly irregular” heart rhythm
- Atrial flutter
- Causes a “sawtooth” pattern on ECG
- Ventricular tachycardia
- Rhythm starts in the ventricles
|SIGNS AND SYMPTOMS OF TACHYCARDIA|
Pediatric tachyarrhythmias are first divided into narrow complex or wide complex tachycardia. Measure the QRS complex on a standard ECG to assess width.
|NARROW QRS COMPLEX
(≤ 0.09 s)
|WIDE QRS COMPLEX
(> 0.09 s)
Narrow QRS Complex
Atrial flutter is an uncommon rhythm distinguished on an ECG as a “sawtooth” pattern. It is caused by an abnormal reentrant pathway that causes the atria to beat very quickly and ineffectively. Atrial contractions may exceed 300 bpm but not all of these will reach the AV node and cause a ventricular contraction.
Most often, PALS providers will have to distinguish between two similar narrow QRS complex tachyarrhythmias—sinus tachycardia and supraventricular tachycardia (SVT). SVT is more commonly caused by accessory pathway reentry, AV node reentry, and ectopic atrial focus.
Wide QRS Complex
Ventricular tachycardia (VTach) is uncommon in children but can be rapidly fatal. Unless the patient has a documented wide complex tachyarrhythmia, an ECG with a QRS complex > 0.09 sec is VTach until proven otherwise. Polymorphic VTach, Torsades de pointes, and “unusual” SVT (SVT with wide complexes due to aberrant conduction) may be reversible (e.g. magnesium for Torsades), but do not delay treatment for VTach. Any of these rhythms can devolve into ventricular fibrillation (VFib). VTach may not be particularly rapid (simply > 120 bpm) but is regular. Generally, P waves are lost during VTach or become dissociated from the QRS complex. Fusion beats are a sign of ventricular tachycardia and are produced when both a supraventricular and ventricular impulse combine to produce a hybrid appearing QRS (fusion beat) (see Fig. 9).