Rhythm Second Opinion

[cannonball88]

Hey Everyone

I might have to say I'm a little stumped on this one. 90 y/o female, general malaise and/or failure to thrive.

Patient has a pacemaker, but I'm not seeing pacer spikes. Obviously with the wide QRS, we're looking at a rhythm that is ventricular in origin, but even at the lower rate, it remains wide. Throughout transport, her rate got as low as 90, as high as 127. Posting two rhythm strips here. Thoughts?

 

[chaz90]

That's a paced rhythm. Pacer spikes are being filtered out by the monitor. What brand of monitor is this?

 

[cannonball88]

LP12. Forgive me if this is a stupid question, but if it's paced, how can it be fluctuating this much in rate? Isn't the rate for a pacer generally set and consistant?

 

[DesertMedic66]

That's a paced rhythm. Pacer spikes are being filtered out by the monitor. What brand of monitor is this?

This is what I would say also. Is there a 12-lead on this patient? For LP12's if you print out a short strip or do a 12-lead the monitor will put in arrows that indicate the rhythm is paced. LP's filter out the pacer spikes

 

[cannonball88]

No 12 lead, but I'll update once the ER does one.

 

[chaz90]

LP12. Forgive me if this is a stupid question, but if it's paced, how can it be fluctuating this much in rate? Isn't the rate for a pacer generally set and consistant?

Not a stupid question at all. Rate responsive and rate modulating pacers are becoming increasingly common. The rhythm strips you're showing look pretty consistent too. Another possibility is that the patient was in and out of this paced rhythm. Many are set to a minimum acceptable rate to kick in, so if the intrinsic rate went above the minimum limit (let's say 100), the pacer wouldn't activate at that higher rate.

 

[cannonball88]

So my next question... Why in the world would my LP12 be filtering out pacer spikes? Is something set wrong?

 

[chaz90]

No, nothing is set wrong. I'm not actually certain there is a way to turn off pacer spike filtering on Lifepaks, but someone else may know more than I do on that. The monitor will (should) indicate the pacer spikes with an arrow on EKG printing.

The take home message should be to perform a 12 lead EKG on this patient. This morphology is pretty specific for pacing, but always check in 12 lead mode, particularly if it looks "funky" or you are unsure. When doing a 12 lead on a rhythm that may be paced, look for possible negative concordance in the precordial leads, a LBBB like morphology in V1, and a left axis deviation. Pacer spikes in 12 lead mode may not be filtered, but may also be much smaller than the massive textbook TCP spikes you may be looking for.

 

[Brandon O]

Modern pacemakers often use small amperages that can easily be wiped by the usual filters. Do not hinge your interpretations upon pacer spikes. Also, with the abundance of pacemaker typs around, you should expect almost any pattern; for instance, they might sense normal atrial activity and pace the ventricles, they might pace both chambers, they might ignore the atrial and pace the ventricles at a set rate... and so on.

 

[cannonball88]

Thank you all for your help.

 

[TomB]

Could be atrial flutter with 3:1 pacing in the first strip and 2:1 pacing in the second. Slight variations in the flutter rate could place sensed atrial events barely inside or outside of the post ventricular atrial refractory period (PVARP) to make it switch back and forth from 2:1 to 3:1 but you'd have to know how the device is programmed to know for sure! Rate modulation could also play a role. For example, if a patient was short of breath the pacemaker could decide that the patient was exercising and allow a higher rate.

 

[Brandon O]

For example, if a patient was short of breath the pacemaker could decide that the patient was exercising and allow a higher rate.

What's the mechanism of that? Detection of motion artifact?

 

[Jason]

Pacemakers and ICDs have had some changes in the last several years.
Your rhythm strips look like a paced rhythm, rate response V-paced rhythm. The LP12 and other monitors have a default filtering setting built in during Monitor Mode. This filtering goes away in 12-Lead Diagnostic Mode. This is the reason why you tend to get more artifact in 12-Leads than just your 4 -5 leads. It's very common to not see pacing spikes in Monitor Mode. A lot of pacemakers only need a low setting of voltage to capture and work. Rates can vary with pacemakers depending on model and setting. Most pacemakers can sense the need to increase rate from sensors in the generator that determine an increase in respiratory rate, or simply greater movement of the chest. It's not specifically the shortness of breath that triggers an increase, but the increase in chest movement; also in patients that are very active or exercise.
Your question is a good one. Keep learning, keep asking.

 

[SandpitMedic]

Your question is a good one. Keep learning, keep asking.

I love the vibe here.

 

[TomB]

What's the mechanism of that? Detection of motion artifact?

There is more than one possible mechanism but some pacemakers monitor intrathoracic impedance between the lead and power plant (tip and can) to measure the respiratory rate. The device assumes that when you are breathing hard you need more cardiac output.

 

[Jason]

In a little more in depth:
Spikes are not usually seen on Monitor mode in EKGs due to Bipolar spikes being hard to visualize, unlike older devices which use Unipolar Polarity.
Impedance measurements across the thoracic cavity are used to measure Heart Failure (fluid retention), ie: Corvue (St Jude) or OptiVol (Medtronic). The lower the impedance, the greater the fluid retention. An inverse relationship.

 

[TomB]

Pacemakers have been using impedance to measure respiratory rate and minute ventilation for a long time.

http://www.ncbi.nlm.nih.gov/pubmed/3608595

 

[Brandon O]

That's way cool. Never occurred to me to put a sensor in the powerplant.