A 49-year-old man was admitted to the cardiology department because of an episode of palpitations, dizziness, and epigastric discomfort. He had no history of heart disease, but he reported episodes of regular palpitations during the past year. His standard 12-lead electrocardiogram (ECG) on admission was unremarkable. Physical examination and routine laboratory examinations, including blood and urine tests, chest X-ray film, and transthoracic echocardiography, were normal. The results of 24-hour Holter monitoring revealed a short-lasting episode of regular tachycardia characterized by a wide QRS complex of 140ms and a cycle length of 300ms.
An electrophysiological study was performed. During pacing at the right ventricular apex with a basic cycle length of 500ms, two extra stimuli given at 305 and 210ms induced a wide QRS complex tachycardia with negative precordial concordance and a cycle length of 313ms (see Figure 1, panel A). Endocardial recordings during the tachycardia showed a 1:1 relationship between ventricular and atrial activity. An eccentric atrial activation sequence was demonstrated, with the earliest atrial activation recorded by the distal coronary sinus catheter, suggesting retrograde atrial activation through a left-sided accessory pathway (see Figure 1, panel B). The HV interval was 81ms and the VA interval was 165ms. A diagnosis of orthodromic atrioventricular re-entrant tachycardia involving a left lateral accessory pathway with left bundle branch aberration was made. Radiofrequency ablation of the accessory pathway was successfully accomplished.
Discussion
Wide QRS complex tachycardia may result from supraventricular tachycardia with bundle branch block (pre-existing or tachycardia-related), supraventricular tachycardia with atrioventricular conduction over an accessory pathway, or ventricular tachycardia.
Evaluation with a 12-lead ECG can support the differential diagnosis of the underlying mechanism, and several ECG criteria have been proposed. Concordance of the predominant direction of wide precordial QRS complexes is a useful ECG clue in differentiating between a ventricular and a supraventricular tachycardia. When all of the ventricular complexes from leads V1 to V6 are positive (positive concordance), the diagnosis is most likely left posterior ventricular tachycardia or, rarely, supraventricular tachycardia with atrioventricular conduction over a left posterior accessory pathway.
Negative concordance is considered diagnostic of a ventricular tachycardia arising from the apical area of the left ventricle.1 However, rare exceptions to this rule have been reported.2–4 In one of these cases, an abnormal anatomical position of the heart due to pectus excavatum in a patient with supraventricular tachycardia and left bundle branch block led to negative concordance in the precordial leads and a false diagnosis of ventricular tachycardia.2 The mechanism of negative precordial concordance in our case is unclear. An anatomical explanation seems unlikely because physical examination did not reveal any abnormalities of the thoracic cavity and a 12-lead ECG showed no frontal axis deviation.
Conclusions
This is a very rare case of broad QRS complex tachycardia with a negative concordant pattern in the precordial leads due to orthodromic atrioventricular re-entrant tachycardia involving a left lateral accessory pathway with left bundle branch aberration. This case shows that the commonly accepted ECG criterion of negative precordial concordance may rarely be misleading, and highlights the importance of electrophysiological study in the differential diagnosis of wide QRS complex tachycardias.