Narrow QRS tachycardia in a patient with manifest Wolff‐Parkinson‐White syndrome

A 46-year-old man presented with paroxysmal tachycardia and severe palpitation. He arrived at our hospital by walking, and had informed that the paroxysmal tachycardia began suddenly while consuming alcohol. Further, tachycardia with palpitation cannot be terminated by resting or holding breath. Physical examinations showed no abnormalities, and the patient's pulse was regular with a rate of approximately 140/min and blood pressure was 110/76 mmHg. Electrocardiogram showed narrow QRS complex for 130/min (Fig. 1). Further, R–R interval seemed regular, but slight right axis deviation was recognized; P wave was recorded by lead V1. The patient's history showed that he was previously diagnosed with the Wolff–Parkinson–White (WPW) syndrome in 2005 during an annual physical examination (Fig. 2); however, there was no record of a history of tachycardia. DC cardioversion was performed during narrow QRS tachycardia, immediately after which we obtained consequent wide QRS complex with delta wave (Fig. 2). Electrocardiogram at arrival to our hospital. Electrocardiogram immediately after DC cardioversion. Same electrocardiographic waves were obtained during an annual physical examination in 2005. Here, we have explained the interpretation of the narrow QRS tachycardia obtained in the electrocardiogram. Fig. 1 shows regular narrow QRS tachycardia with approximate heart rate of 130/min; ST elevations were recognized in leads V1–V4 and P wave appeared to be recorded by lead V1, but the other leads recorded positive large waves before each QRS complex. When observing an electrocardiogram with the above, the following conditions need to be considered: sinus tachycardia, atrial tachycardia, atrial flutter, and paroxysmal supraventricular tachycardia. Since the patient specified sudden onset of palpitation, the narrow QRS tachycardia may be re-entrant tachycardia. Therefore, we excluded sinus tachycardia. Further, information from the medical history of the patient on WPW syndrome aided the diagnosis of paroxysmal supraventricular tachycardia, including atrioventricular reciprocating tachycardia. Further, if the narrow QRS tachycardia was atrioventricular reciprocating tachycardia, a retrograde P wave should be recognized after the QRS complex. However, the P wave was not only observed after the QRS complex but also after the positive large waves that were previously identified as appearing before each QRS complex. This proved the presence of atrial flutter waves. By considering the presence of atrial flutter, the electrocardiogram (Fig. 1) could be interpreted as atrial flutter with 2:1 atrioventricular block [1]. However, atrial flutter can be differentiated from atrial tachycardia by the atrial excitation rate; atrial excitation of over 240/min is considered as atrial flutter. Since the atrial excitation rate in our patient was 270/min, we considered the rhythm observed in the electrocardiogram as atrial flutter [2]. In addition to atrial flutter or fibrillation observed in the electrocardiogram of a patient with WPW syndrome, wide QRS tachycardia can be observed, which is referred to as pseudo-ventricular tachycardia or flutter [3]. However, Fig. 1 shows that even narrow QRS tachycardia occurred in a patient with WPW syndrome. Moreover, after DC cardioversion, a wide QRS complex with delta wave appeared immediately (Fig. 2), which means that the atrial excitation wave during tachycardia was not conducted via the accessory pathway, but instead via the atrioventricular node to the ventricle. The most probable explanation could be that the effective refractory period of the accessory pathway was longer than that of the atrioventricular node. Therefore, if atrial excitation rate increased, then the atrial excitation wave would not be conducted through the accessory pathway but rather through the atrioventricular node to the ventricle, which results in narrow QRS tachycardia. Finally, the location of this weak accessory pathway was the left posterior wall along the atrioventricular ring [4]. None Declared.