Differences in Treadmill Exercise Tolerance Parameters Between Patients With Partial and Advanced Interatrial Depolarization Abnormality Asim Raja, MD a , Vignendra Ariyarajah, MD b, *, Jaxon Fernandes, MD c , Sirin Apiyasawat, MD d , Aliasghar Khadem, MD b , Ivan Barac, MD b , and David H. Spodick, MD, DSc c Advanced interatrial block (aIAB) is considerably much less common than partial inter- atrial block (pIAB), occuring in <2% of the elderly hospitalized population. Less is, therefore, known of the true clinical burden of aIAB, particularly in relation to graded exercise. Therefore, 12 patients with aIAB and 30 patients with pIAB who performed a baseline exercise tolerance test and had a repeat test performed >2 years later were included in the study. Exercise tolerance, echocardiographic findings, and major adverse cardiovascular events were compared. Left atrial size progressed at a significantly faster rate in those with aIAB. In addition, Duke Prognostic Treadmill scores were significantly lower on follow-up in those patients with aIAB. Overall, patients with aIAB had signifi- cantly greater left atrial size (48.3  9 vs 42.8  4 mm, p <0.01) and significantly lower Duke Prognostic Treadmill scores than those with pIAB (0.2  5 vs 4.1  4, p <0.05). There were, however, no significant differences in the occurence of major adverse cardio- vascular events. In conclusion, left atrial size progressed at a significantly faster rate but Duke Prognostic Treadmill scores were significantly lower in those with aIAB compared with patients with pIAB after >2 years of follow-up. Further study is required to determine whether patients with aIAB require follow-up echocardiography and/or exercise tolerance tests for optimal risk stratification. © 2008 Elsevier Inc. All rights reserved. (Am J Cardiol 2008;102:866 – 870) Interatrial conduction delay or interatrial block (IAB) de- notes abnormal atrial depolarization resulting from impaired sinus impulse transmission between the right and left atrium (LA). 1 IAB is diagnosed when P waves 110 ms are present on the electrocardiogram. 2 In partial IAB (pIAB), P waves are prolonged and commonly notched, but in ad- vanced IAB (aIAB), they are not only prolonged but are also biphasic (+-) in leads II, III, and aVF 1 (Figure 1). IAB is associated with atrial fibrillation, 3 LA enlargement, 4 and electromechanic dysfunction, 5 myocardial ischemia during treadmill exercise tolerance tests (ETTs), 6–9 and is a risk for embolic stroke. 10 Occuring in 2% of the elderly hospital- ized population and in 0.3% of the general hospital pop- ulation, 1 aIAB is much less common than pIAB and, there- fore, less is known of its associations and true clinical burden, particularly in regard to major adverse cardiovas- cular events. Methods Between January 2003 and June 2004, we identified 27 consecutive patients at a tertiary care hospital (Saint Vin- a Department of Medicine, b Division of Cardiology, St. Boniface Gen- eral Hospital, University of Manitoba, Winnipeg, Manitoba; c Department of Medicine, Division of Cardiology, Saint Vincent Hospital, University of Massachusetts, Worcester, Massachusetts; d Department of Medicine, Di- vision of Cardiology, Columbia University College of Physicians & Sur- geons, New York, New York. Manuscript received March 11, 2008; revised manuscript received and accepted May 7, 2008. Professor Spodick receives research support from St. Vincent Hospital, Worcester, Massachusetts. *Corresponding author: Tel: 204-510-2235; fax: 204-231-3006. E-mail address: vignendra@hotmail.com (V. Ariyarajah). Figure 1. Types of IAB. (A) In pIAB, impulses continue to pass from the right atrium to the LA via interatrial relays but are delayed (110 ms). (B) In aIAB, impulse conduction across interatrial relays are so severely delayed that they are directed to the atrioventricular node first before progressing caudocephalically to depolarize the LA. This results in bipha- sic (+-) P waves (110 ms) in leads II, III, and aVF. 0002-9149/08/$ – see front matter © 2008 Elsevier Inc. All rights reserved. www.AJConline.org doi:10.1016/j.amjcard.2008.05.026