To the Editor:
We thank Khalid and colleagues for their insightful letter, emphasizing the importance of total electrical alternans and vector alternans in the diagnosis of cardiac tamponade. Electrical alternans has diverse mechanisms and is present in various conditions ranging from coronary ischemia, atrioventricular tachycardia, to large pericardial effusion.1 Both electrical alternans and vector alternans, as mentioned by the authors, are highly specific findings, but its absence does not exclude cardiac tamponade.
In our study among patients with large pericardial effusion, the specificity of electrical alternans for detecting tamponade was 86%, whereas the sensitivity was only 24%.2 The positive predictive value of electrical alternans was 95% for the presence of tamponade, but its negative predictive value was only 9.5%.2
The finding of high specificity and low sensitivity of electrical alternans for cardiac tamponade has been reported by others as well.3, 4 Unfortunately, we did not classify our alternans patients to see how many had amplitude alternans vs vector alternans, or total alternans for that matter. Therefore, we do not know how many of our study patients had each type of alternans.
We only assessed electrocardiogram findings in the setting of echocardiographic evidence of tamponade; therefore, its comparison with other studies using clinical criteria for tamponade may not be applicable.
Syed Wamique Yusuf, MBBS, MRCPI Smita I. Negi, MD Jose Banchs, MD Rahul G. Argula, MBBS, MPH MD Anderson Cancer Center Department of Cardiology University of Texas Houston, Texas Rahul G. Argula, MD Division of Pulmonary Critical Care, Allergy and Sleep Medicine Medical University of South Carolina Charleston, South Carolina
References
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