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Glenview, IL
Dr. Soffer is a Clinical Professor of Medicine, Chicago Medical School.
Correspondence to: Alfred Soffer MD, Master FCCP, 950 Central Rd, Glenview, IL 60025; e-mail: xiss{at}sbcglobal.net
Echocardiography has replaced the phonocardiogram as the clinician’s diagnostic method of choice. Sophisticated radiologic procedures have relegated routine office fluoroscopy to a position of historical curiosity. However, a technique introduced 100 years ago retains vital clinical relevance. On March 22, 1905, Wilhelm Einthoven recorded the first ECG from a healthy man. Elegant machines have supplanted his simple string galvanometer, but perusal of the traditional P-QRS-T pattern is still the basis for obtaining important information in our evaluation of acute and chronic cardiac disease.
Recent investigations offer the promise of new insights that the ECG can provide. The report by Ariyarajah and associates in this issue of CHEST (see page 971) indicates that certain alterations in the P wave have grave associations with atrial arrhythmias and congestive heart failure. Apparently, however, these findings have not been widely recognized and have not received the attention they deserve.
Interatrial block is prolonged conduction between the right and left atria. A P-wave duration of > 120 ms identifies such blockage and is associated with wide, notched, or biphasic P waves. Jarath and Spodick1 and Asad and Spodick2 studied two general hospital populations and reported a 47% prevalence of interatrial block in patients who were in sinus rhythm among patients of all ages, and 59% in patients 
60 years of age. This is a much higher prevalence than the figures cited by many previous investigators. Presumably, therefore, this finding may have been widely overlooked, and indeed many textbooks in general medicine and cardiology do not mention interatrial block. Underreporting may have occurred by restricting studies to lead 2 alone or to only one or two other leads. This phenomenon can appear in any lead, and since sensitivity increases with the number of leads used, a full 12-lead ECG should be viewed.
The left atrial dynamics of a control group of patients without interatrial block was compared to subjects with known block.3 Although both groups had the same atrial volumes and diameter, the cohort with block had lower stroke volumes, ejection fractions, and left atrial kinetic energy. The authors concluded that interatrial block is associated with a sluggish, poorly contractile left atrium and a lessened atrial "kick." In addition, the late activation of the left atrium results in a delay in left ventricular filling. These electromechanical changes increase the risk of congestive heart failure, and the clinician can be alerted to such potential by observing the clue presented by the presence of the interatrial block.
The relationship of interatrial block to atrial arrhythmias has clinical significance because prolonged atrial conduction can be an etiologic basis for the appearance of atrial flutter or atrial fibrillation. Susceptibility to these abnormal rhythms is present when there is aberrant conduction between the atria. Whether chronic or acute, such arrhythmias predispose the patient to the development of atrial thrombi and the risk of stroke. Awareness of the arrhythmic potential of interatrial block can enable the clinician to anticipate and possibly prevent these complications.
In their report, Ariyarajah et al emphasize the need for data from controlled clinical trials. Is immediate therapy indicated, and if so, what is the role of therapy with pacing or angiotensin-converting enzyme inhibitors? What about prophylactic anticoagulation therapy? The absence of such information means that currently we do not have guidelines for managing patients with interatrial block. Future investigators will surely include electrophysiologic techniques in their research. However, electrophysiologic techniques are not appropriate for use as a screening method for studying the general population. For this need, Eithoven‘s apparatus retains admirable utility. In both the office and hospital, careful scrutiny of the 12-lead ECG can enhance the clinician’s awareness of the potentially dangerous consequences of interatrial block.
References
This article has been cited by other articles:
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  T. O. Cheng Einthoven's Machine Is Alive and Well Today, Although His Contemporaries Were Not Interested In It At All. Chest, April 1, 2006; 129(4): 1114 - 1114. [Full Text] [PDF]
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