Holter monitor
If the symptoms are present while the person is receiving medical care (e.g., in an emergency department), an ECG may show typical changes that confirm the diagnosis ie, QRS duration &lt;120 ms, unless a heart block is suspected. If the palpitations are recurrent, a doctor may request a Holter monitor (portable, wearable ECG recorder). Again, this will show the diagnosis if the recorder is attached at the time of the symptoms. In rare cases, disabling but infrequent episodes of palpitations may require the insertion of a small device under the skin that continuously record heart activity (an implantable loop recorder). All these ECG-based technologies also enable the distinction between AVNRT and other abnormal fast heart rhythms such as atrial fibrillation, atrial flutter, sinus tachycardia, ventricular tachycardia and tachyarrhythmias related to Wolff-Parkinson-White syndrome, all of which may have symptoms that are similar to AVNRT.