Heart Blocks ECG 3
- Normal sinus rhythm
- Non-conducted premature atrial contractions (blocked PACs)
If a premature atrial contraction occurs when the AV node has not yet 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 occurring 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.
Related Topic Reviews: Premature Atrial Contractions