Pacer capture

[hotcoffee]

Took care of a CT surgery patient with an epicardial pacer connected but on backup rate of 35 VVI. She was alert and doing great.

At shift change we check thresholds. The patients intrinsic rate was about 60 so we set the rate at 70 and were checking the capture threshold. As we turned down past 1.5 mA I could see the EKG rate drop from 70 to the 60s and the pulse ox "pulse" rate drop to 60. Also the Qrs narrowed and changed morphology (looked intrinsic rather than LBBB/paced).

so to me we had lost capture and 1.5 was the threshold.

The other nurse said that because there were pacing spikes followed by a Qrs we still had capture at 1.3mA even though the patients rate dropped to 60!?

what do you think Internet?

[MYSTICOOKIEBEAR]

When talking about a VVI backup, capture is when you have a QRS after every spike, 100% of the time.

If you set the VVI backup to 70 and it drops down to their intrinsic rate, you have lost 100% capture. Granted you could still be capturing but if it's not 100% then you need to crank the output up. If you turned the rate to 100 and there was still a QRS with every spike, but the patient is still at their intrinsic rate of 60, you do not have 100% capture. For all intents and purposes, and in the traditional sense, you DO NOT have capture.

[hotcoffee]

That's what I was saying! Thank you.

so the capture threshold is the lowest possible mA at which you have capture.

i think you need mechanical as well as electrical capture which can be verified via art line, pulse ox or just a finger on the pulse.

[offlabel]

When you do this, pace well over the patient's native rate. You say it was 60. Pace at 90 to get a more clear picture of what is going on sooner. This is so you don't take as long and so you won't have such a large drop in CO while V pacing. You'll compensate for the less efficient impulse conduction with the higher rate.

[hotcoffee]

My patient's rhythm was juncitonal/3degree block so I doubt there was much atrial kick. I imagine VVI wouldn't cause a drop in output.

thanks for the responses

[offlabel]

You might be surprised about that.

Even with a 3rd degree block with a ventricular rate of 60, the native ventricular conduction pathway is intact. That means that the speed of conduction of the impulse and the coordination of ventricular contraction is superior to the slower conducted, discoordinated impulse/contraction that comes from an epicardial pacer wire.

Just look at the morphology of a normally conducted QRS and a VVI QRS. The normal one is narrow, which means it's much faster and efficient than the wide, slower and less coordinated one.