Atrial Arrhythmias ECG 20
1. Normal sinus rhythm
2. Non-conducted premature atrial contractions (blocked PACs)
If a premature atrial contraction occurs when the AV node has not yer recovered from the refractory period, the PAC will fail to conduct to the ventricles and there will not be a QRS complex afterwards (or the ectopic PR interval will be prolonged, as in the second QRS complex on this ECG). The ECG will show a premature, ectopic P wave occuring and then no QRS complex afterwards. When this occurs in a pattern of bigeminy, the interpreter may be fooled into thinking that sinus bradycardia is present, since every other beat is a non-conducted PAC and the QRS rate is quite slow.