ECG Challenge: Crackling Lung Sounds and Edema

A 62-year-old man with a history of dilated cardiomyopathy and a left ventricular ejection fraction (LVEF) of 30% presents to the emergency department with complaints of shortness of breath and weight gain. 
His physical examination demonstrates bilateral peripheral edema in the knees. Lung examination demonstrates bibasilar rales. He begins intravenous furosemide and is admitted to the hospital for additional therapy. A routine ECG is obtained.
The correct diagnosis is sinus rhythm with IVCD (Figure 2).
The rhythm is regular at a rate of 80 beats/min. A P wave occurs before each QRS complex (+) and is positive in leads I, II, aVF, and V4-V6, so this is a normal sinus rhythm. The PR interval is constant (0.16 sec). 
The QRS complex duration is increased (0.16 sec) with a normal axis between 0° and +90° (positive QRS complex in leads I and aVF). The QT/QTc intervals are prolonged (440/510 msec) but are normal when the prolonged QRS complex duration is considered (380/440 msec), ie the QRS duration is 60 msec longer than the normal QRS duration and this 60 msec should be subtracted from the measured QT interval before correcting for heart rate. 
The QRS complex has LBBB morphology with a deep S wave in lead V1 and a broad R wave in leads I and V6. However, there is a prominent septal R wave in lead V1 (→) and septal Q waves in leads V4-V6 (↑). Septal waveforms are caused by impulse activation resulting from a septal or medial branch that comes from the left bundle. Normally, the first part of the ventricle to be activated is the left septum, resulting from impulse activation via the septal branch. This presents with initial small Q waves in leads I, aVL, and V5-V6 and a septal R wave in lead V1. 
With an LBBB, septal forces are not seen because the septal or median branch that innervates the septum arises from the left bundle. If there are septal forces, the wide QRS complex results from nonspecific IVCD rather than an LBBB. 
When the QRS complex is very wide, the IVCD is often caused by dilated cardiomyopathy. Of note, an IVCD is due to slowing of conduction via the His-Purkinje system. Because ventricular activation occurs normally via the His-Purkinje system, abnormalities affecting the left ventricle can be diagnosed. In contrast, with an LBBB impulse, conduction into the left ventricle does not occur via the His-Purkinje system but results from direct myocardial activation. Therefore, left ventricular abnormalities cannot be reliably established.
Philip Podrid, MD, is an electrophysiologist, a professor of medicine and pharmacology at Boston University School of Medicine, and a lecturer in medicine at Harvard Medical School. Although retired from clinical practice, he continues to teach clinical cardiology and especially ECGs to medical students, house staff, and cardiology fellows at many major teaching hospitals in Massachusetts. In his limited free time he enjoys photography, music, and reading.