Half a Million ECG Interpretations and Still Learning

August 17, 2016 | Mary L. Dohrmann, MD, FACC

Many things inspire medicine residents to become cardiologists – a specific patient, a mentor, the science of cardiovascular medicine. In my case, it was the electrocardiogram (ECG). For me, ECG interpretation blended all that is known about the heart for an individual patient after obtaining a thorough history and physical examination. Upon entering my cardiovascular medicine fellowship at Duke University in July 1977, I had a solid background in ECG interpretation, thanks to the mentorship of Richard Martin, MD, at the University of Missouri. He emphasized vector analysis of the ECG, based on Grant's method. I wouldn't think of having an ECG interpretation session without having drawn the vector analysis for the ECG. I read and underlined Grant's Clinical Electrocardiography many times. J. Willis Hurst, MD, FACC's commentary several years ago underscored the importance of vector analysis for proper ECG interpretation, a skill which today's trainees have now put aside for recognizing the core ECG abnormalities to be tested on their future board exam in cardiovascular medicine.

It was at Duke that Joseph C. Greenfield, Jr., MD, FACC, impressed upon me how much I didn't know about the ECG. He asked me at my first sit-down interpretation session, "What makes you think you know more than the computer?" after he noted that I had struck-through most of the computer derived ECG statements! That challenge inspired me to understand what criteria the computer could use to make any statement, including magnitude and direction of vectors, angle differences between QRS and T wave vectors, areas under curves, tangents to ST segments. Yes, the ECG is a combination of all that algebra and calculus (and vectors) that you thought you didn't need to know any more!

My Duke fellowship also taught me the importance of using probability theory, that the prevalence of disease in a population influences the likelihood of the disease being present. Age and gender influence how I interpret an ECG – I think twice before labelling a 32 year-old with left ventricular hypertrophy on an ECG.

Thirty-nine years later and after more than a half a million ECG interpretations, what advice do I have for new trainees? I challenge you to use every ECG as an opportunity to discover something about the patient, about the ECG itself, and about your knowledge. Approach the ECG the same way every time, systematically, taking into account all available information, questioning why the computer says what it does (it has trouble with atrial fibrillation, too). Fortify yourself with real knowledge – read an ECG textbook (my favorite is Marriott's), read the American Heart Association's recommendations for standardization and interpretation of the ECG , find an old copy of Grant's and practice drawing some vectors! In three years, the Accreditation Council for Graduate Medical Education requirements for cardiovascular medicine training suggest you interpret at least 3500 ECGs. That is only three to four ECGs per day! After interpreting a half a million ECGs, I am still seeing ECGs I have never seen before.

This article was authored by Mary L. Dohrmann, MD, FACC, professor of clinical medicine in the division of cardiovascular medicine at the University of Missouri School of Medicine, in Columbia, Missouri.