br Comments Fig shows regular narrow QRS tachycardia
Comments Fig. 1 shows regular narrow QRS tachycardia with approximate UNC 0642 manufacturer 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 . 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 . 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 . 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 .
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