Supraventricular tachycardia

Supraventricular tachycardia is the most common form of tachyarrhythmia. It is characterized by a heart rate of 200–300 beats/min

Supraventricular tachycardia may be due to an autonomous focus, in which case the rhythm is monotonous, or due to a re-entry mechanism, in which case sudden conversion from an abnormal to a normal rhythm can be seen

Sustained tachycardia is associated with suboptimal ventricular filling and decreased cardiac output. These result in atrial overload and congestive failure. Sustained tachycardias of greater than 200 beats/min frequently result in fetal hydrops. The combination of hydrops and dysrhythmia has a poor prognosis with mortality of about 80%

Doppler assessment of the fetal ductus venosus during the supraventricular tachycardia demonstrates reversed a-wave with loss of the normal triphasic waveform. The earliest sign of therapy success is the reappearance of triphasic venous flow, followed by return to normal heart rate and finally resolution of post supraventricular tachycardia cardiomyopathy