This three-lead rhythm strip is from an 85 year-old-woman for whom we have no other information, unfortunately. It shows an obvious, regular bigeminal pattern. There are many rhythms that can cause bigeminy, with regular, paired beats. So, how do we analyze this rhythm?
This ECG is from an 88-year-old man with congestive heart failure. No other clinical information is known. It shows an underlying sinus rhythm with atrial bigeminy - every other beat is a premature atrial contraction. There is very little, if any, difference in the morphology of the sinus P waves and the ectopic P waves, indicating that the ectopic focus is in the vicinity of the sinus node. There is no "compensatory" pause, because PACs penetrate the sinus node, resetting it. So, the underlying sinus rate here is about 72 beats per minute.
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.
To continue a recent theme, we offer this ECG, which appears on quick glance to be an atrial bigeminy. On closer inspection, we do not see ectopic P' waves in the second conducted beats of each pair. In fact, the P waves look the same in both the first and second beats. However, if you look very closely (we enlarged the screen), you may notice that the second T wave of each pair is slightly larger with a slightly different morphology than the first T wave. If this distortion of the second T waves represents a PAC, the PAC is non-conducted and concealed in the T wave.
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