Pseudo-first degree AV block

Figure 1 - 30 sec continuous strip

This looked like sinus bradycardia (~44 bpm) with a very long PR interval (800 ms or 0.80 sec) or first degree AV block.

Figure 2 - 30 sec continuous strip few minutes prior to the strip in Figure 1

In #1, a distinct P wave can be seen in R2 but you will note that it merged with the QRS. Because of the merging, the shape of the QRS is distorted. In #2 and #3, the P wvave can be seen after the QRS. On the last QRS complex, the P wave is seen farther awway from the QRS. The QRS are junctional complexes. So, there is AV dissociation. The rate of the sinus beat is almost the same with the junctional rate. This is called isorrhythmic AV dissociation.

The ECG strip in Figure 1 is not a true first degree AV block but a pseudo-first degree AV block. The strips are sinus bradycardia with junctional beats creating AV dissociation (isorhythmic AV dissociation)

After a few hours (of stopping a beta-blocker), the sinus rate increased to about 60 and captured the ventricles. 

#626