P waves

[Ian]

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I was reading Garcia's ECG book earlier and in discussing rhythms, he said that the presence of P waves tell you that the rhythm in question has some atrial or supraventricular component. Aren't P waves normal? Does he mean the absence of P waves?

 

[TallScrubs]

Granted, I'm no expert, but yes, P-waves are normal. When reading EKG you want to assess where the rhythm is originating from, and P-waves indicate that pace is coming from SA node. No P-waves = no atria contracting = rhythm originating from AV or lower.

Hope that helps.

 

[Ian]

Thanks, I think I understand it now. Initially I thought it meant that the presence of P waves means the arrhythmia is supraventricular/atrial in nature.

 

[TallScrubs]

It can. If you note the presence of an arrhythmia w/ P-waves, it is SV/atrial in nature. P-wave denotes sinus-rhythm.

 

[dumptruck]

P waves don't necessarily mean it's a sinus rhythm. For example, in 3rd degree block you'll have P waves totally dissociated from the ventricular activity.

To your original question, the sentence you quoted is correct. P waves indicate atrial electrical activity. This could mean sinus pacing, or some other ectopic site(s) before the AV junction.

 

[MrBeauregard]

P waves don't necessarily mean it's a sinus rhythm. For example, in 3rd degree block you'll have P waves totally dissociated from the ventricular activity.

To your original question, the sentence you quoted is correct. P waves indicate atrial electrical activity. This could mean sinus pacing, or some other ectopic site(s) before the AV junction.

Absolutely. The presence of a P-wave does not mean there is sinus rhythm. "Wandering Pacemaker" is a rhythm that originates in the atria but has multiple sites which contribute to the depolarization that travels down the AV node to the ventricles. As a result, the rhythm contains P-waves but each P-wave actually looks different because each depolarization is originating from a different site of automaticity within the atria.

 

[Rendar5]

p-wave as Garcia said is atrial depolarization. this means that the depolarization origin has to be at or above the A-V node. once the origin goes below that there will never be p-waves.

A P-wave does not necessarily indicate sinus activity. If you look at the axis of the p-wave and the P-R interval, you can make the determination if it originates from the SA node or not.

However, you do not need to know this much detail for med school. For med school, you simply need to know that a p-wave indicates atrial depoloarization.

 

[manpuper]

it can of course.

 

[pinipig523]

P waves means atrial depolarization, that's all. Whether or not the atria is causing downstream depolarization of the ventricles as a "sinus rhythm" is a whole 'nother story.

Look for P waves in V1 best. Sometimes these are best for when the limb leads show an "SVT-looking" ekg.

P wave morphology can tell you about the activity in the atria as well. Dichrotic P may suggest atrial enlargement if in certain leads, a P wave inversion in the I/II may suggest an ectopic pacer in the atria, perhaps something that may cause an atrial flutter rhythm.

If you really want to learn about EKG reading and interpretation, you can ask your cardiologist or cards fellow. But something a little more useful (for me anyway) is Amal Mattu's EKG book with 200 strips that allow you to challenge your reading prowess.

 

[Ian]

Thanks everyone. I'm still working my way through Garcia's book. I'll look into those other books after this.

 

[PMPMD]

Lead II is also good for looking for P's.