This rhythm strip offers two leads taken at the same time, Lead II and Lead V1. The Lead II strip may not look "typical" to a beginning student, because the sinus beats are very small and biphasic. This is due to an axis shift, which cannot be evaluated without more leads.
Premature ventricular contraction
This ECG shows an underlying rhythm of normal sinus rhythm at a rate of 80 / min. There are two premature ventricular contractions (PVCs). The sinus rhythm actually continues uninterrupted, causing a “compensatory pause”. If you march out the P waves, you may even see hints of the hidden P waves in the ST segments of the PVCs. The P waves that occur in the ST segments of the PVCs land in the refractory period of the ventricles, and so are unable to continue into the ventricles and cause a QRS.
This ECG, kindly donated by Dr. Ahmed from India, is from a 70-year-old man shows a sinus rhythm at 80 bpm with left bundle branch block (LBBB), left atrial enlargement (LAE), and a premature ventricular contraction (PVC). The ECG criteria for LBBB is: 1) Wide QRS - greater than or equal to .12 seconds; 2) Supraventricular rhythm; 3) QRS that is negative in V1 and positive in Leads I and V6. In leads with a positive QRS, we will see some ST depression, and in leads with a negative QRS, some ST elevation.
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