A 5-month-old pale and lethargic male infant is brought to emergency. On examination, HR is 240 bpm and it does not change with crying. Lungs are clear and no hepatomegaly present. His ECG is given below. Which of the following is the first step in management of this patient?

ECG s/o Supraventricular tachycardia Characterized by rapid hea rate (about 250 beats per minute)and a consistent P wave for each QRS complex. Prolonged SVT can lead to hea failure with hepatomegaly and respiratory compromise. Fetal SVT can lead to hydrops fetalis. The first-line treatment is to stimulate the vagus nerve using techniques such as carotid massage, immersion of the face in cold water, or voluntary straining. Rapid infusion of IV adenosine can affect resolution if the maneuvers are not successful. Verapamil is contraindicated in this age group, as it may cause acute hypotension and cardiac arrest. Synchronized DC cardioversion may be performed in patients in shock or with hea failure; it must, however, be synchronized to the QRS complex. Transthoracic pacing is useful in bradyarrhythmias.