EKG interpretation - Sinus Block vs PAC?



I was wondering if anyone can help me determine the difference between sinus block and premature atrial contractions. When I was trying to interpret a rhythm strip, I thought it was a sinus block but it turned it to be a PAC. So question is... how do I determine the REAL difference between the two?

And what is an atrial escape beat?

Thanks for any help!


Specializes in Hem/Onc/BMT. Has 11 years experience.

One distinguishing feature would be that in PAC, you'll see the abnormal beat before the expected next wave. Hence, "premature" contraction. On the other hand, in sinus block, you'll see regular p-p interval and then a drop.

But I'm sure there are better answers. It's been too long since I used any EKG knowledge.

Try googling. I remember utilizing many good ECG interpretation websites during school.

Edited by tokebi

Esme12, ASN, BSN, RN

Specializes in Critical Care, ED, Cath lab, CTPAC,Trauma. Has 41 years experience.

Here are a couple of sites you will find helpful. The RNceus is free if you don't want the test and the CEU's

Interactive Online Continuing Education for Nurse Professionals


PAC's originate in the atrium/SA node. They are early.....premature in compairison to the other beats and there is no compensatory pause (3 regular beats combined).

Premature atrial contractions (PACs), also known as atrial premature complexes (APC) or atrial premature beats (APB), are a common cardiac arrhythmia characterized by premature heartbeats originating in the atria. While the sinoatrial node typically regulates the heartbeat during normal sinus rhythm, PACs occur when another region of the atria depolarizes before the sinoatrial node and triggers a premature heartbeat.

On the EKG, PACs are characterized by an abnormally shaped P wave. Because the premature beat initiates outside the sinoatrial node, the associated P wave appears different from those seen in normal sinus rhythm. Typically, the atrial impulse propagates normally through the atrioventricular node and into the cardiac ventricles, resulting in a normal, narrow QRS complex.

Sinus block......which sinus block? Mobitz Type I or Mobitz type II or Mobitz type III

Do you mean Sinus arrest/pause/block?

Sinus arrest is a transient pause in sinus node activity. Sinus arrest is recognized on the EKG as an isoelectric line of variable duration with no P waves or QRS complexes. The pause is usually followed by an AV-nodal escape beat or a new sinus node beat.

Sinus arrest may look like a sino-atrial (SA) block. In SA block the sinus activity is preserved, but the impulses are blocked resulting in missed P waves and QRS complexes. However, in SA block the pause seen on the EKG will represent a multiple (whole number) of the preceding P-P interval. This relationship is absent in sinus arrest.

AgentBeast, BSN, RN

Specializes in Cardiology and ER Nursing. Has 8 years experience.

pac.gifPAC's are often hidden within the T wave of the preceding cardiac cycle.

The 3rd and 7th beat of this strip would be a textbook example of PAC's.