ECG Challenge: A 56-year-old woman with a history of asthma and mild chronic obstructive pulmonary disease presents to the emergency department with increased shortness of breath. Her chest x-ray shows an effusion in the left lower lobe, consistent with aspiration pneumonia. Her pulse is noted to be rapid, and a 12-lead ECG is obtained.
The rhythm appears to be regular; however, it can be noted that there is slight irregularity (ie, the RR intervals are 0.40 s [┌┐] alternating with 0.44 s [↔] in a repeating pattern). Therefore, the rhythm is regularly irregular and the average rate is 138 bpm. The QRS complex duration is normal (0.08 s), and there is a normal morphology. The axis is leftward between 0° and –30° (positive QRS complex in leads I and II and negative in lead aVF; this is a physiological left axis). The QRS complex voltage is increased in lead V5 (25 mm; ]), which is 1 of the criteria for left ventricular hypertrophy (ie, an S wave or R wave in any one precordial lead ≥25 mm). In addition, the S wave in lead V3 ([) is 25 mm. The SV3+RV5=50 mm, which is another criterion for left ventricular hypertrophy (S wave+R wave in any 2 precordial leads ≥35 mm). The QT/QTc intervals are normal (260/390 ms). There are P waves seen before each of the QRS complexes (+, ^), but every other P wave has a different morphology. The P wave following the longer RR interval (+) is positive in leads I, II, aVF, and V4 through V6. Hence, these are sinus complexes. The PR intervals are constant (0.14 s). The alternating P wave (^) after the shorter RR interval is negative in leads I, II, aVF, and V4 through V6. Hence, these are not sinus P waves, but they originate from somewhere else in the atrial myocardium. These are premature atrial complexes. The PR interval associated with these complexes is also constant but slightly longer (0.20 s). Hence, this is a normal sinus rhythm with a sinus rate of 68 bpm, and every other complex is a premature atrial complex (ie, atrial bigeminy). As the premature atrial complexes are not followed by a pause and do not alter the PP interval, they are said to be interpolated premature atrial complexes (in a bigeminal pattern).
Please go to the journal’s blog, OpenHeart, for more ECG Challenges: http://goo.gl/tQPNFp. Challenges are posted on Tuesdays and Responses on Wednesdays.
- © 2016 American Heart Association, Inc.