Thursday, February 14, 2008

My Valentine's Story

It was just your routine defibrillator check at first. Then the screen showed the device had fired.

"You mean I was shocked?"

"Yep."

"When?"

"Three weeks ago, on the 23rd, at 06:38AM and 12 seconds."

"But I didn't feel anything. Just a minute, let me check my calendar." She flips through her calendar, mind scrambling. "I was in Florida. That was the day I went to the spa. I felt fine."

"Remember when you got up that day?"

Hestitating. "I'm not sure. I never had a shock before. Are you sure this thing fired?"

"Yep. Here's what the device recorded:"

(Click to enlarge)


"Why did this happen?"

"I'm not sure. As you know you have atrial fibrillation and a weak heart muscle though you were never found to have coronary artery disease (blocked arteries) - that's why the defibrillator was installed."

"Yes."

"Well, if we look at the tracings, I notice two small clues as to what happened. See those little VS notations?"

"Yes."

"Well those occur every time one of your heart beats are sensed by the device. If there's an FS, that means a heart beat was detected that was above the ventricular fibrillation cutoff rate (in other words, it was going really fast). The TF also means that the heart rate fell into a very fast ventricular tachycardia zone. A VP notation means the device paced your heart. Now, see the 'FD' as the first label on the bottom of the seond line of tracings?"

"Yes."

"Well that means that enough fast heart beats occurred to satisfy the device's algorithm to call this rhythm ventricular fibrillation - the FD stands for 'Fib Detect.' Note how the device then stops labelling the sensed ventricular beats as FS's as it charges to deliver a shock(the labels turn back to VS's but the rate still looks really fast.) Once the charge ends, a CE label is displayed. The device looks for one more fast heart beat, and when it sees it, it delivers its charge, labeled as 'Charge Delivered,' or CD on the next sensed rapid ventricular beat to reset the rhythm. That's when the shock occurs that most people feel. Then we can see your own normal ventricular sensed (VS) beats after the shock is delivered."

"Amazing."

"Yes ma'am, it is. Happy Valentine's Day."

"Oh my God, you're right! I can't believe it! I really just can't believe it!"

* * *

So what programming change was made to her device to prevent another shock? It was a single-chamber Medtronic ICD programmed with backup ventricular pacing at forty beats per minute.

Any takers?

-Wes

Addendum: For those not accustomed to viewing the information produced by interrogating a defibrillator after a shock, the top two lines on each strip represent the signal seen (1) from the tip electrode to the can of the device, simulating an EKG lead, and the lower line (2) is the signal seen locally inside the heart between closely spaced electrodes on the lead (these lines are not "on" at first until a rapid rhythm is detected). The lowest line is the "marker channel" that demonstrates how each blip on the middle signal line was interpreted by the device.

5 comments:

Jay said...

Wes,

I'd raise the pacing rate up to 60 or so to prevent the "long-short" but I'd wouldn't go so far as to say that this would prevent any further shocks. One would also have to weigh the potentially detrimental effect of an increase frequency of RV pacing in this decision.

The main message to the patient here is "congratulations" with a pat on the back. In our office, we'll hang a red constuction paper heart on the wall with the date of the event for all to see. We have patient ask all the time about our wall of hearts and this kind of puts things into perspective.

Jay

DrWes said...

Jay-

What a great idea - the red heart and all. Lots of folks can derive comfort in the fact that they're not alone living with these devices. As miraculous as they are, they still make us confront our mortality - and that's a mind-blowing experience.

Regarding the programming change - I agree with you the "pause was the cause" for her arrhythmia. The two options for this device was to increase the lower rate, as you suggested, or programming on this device's "Ventricular Rate Stabilization" feature that effectively does the same thing. Certainly, adding antiarrhythmics is NOT necessary given the way this arrhythmia started with a pause, then a few more rapid beats, then another pause (the "two clues"), and then the tightly-coupled PVC that induced ventricular fibrillation (Torsades) which was successfully defibrillated.

Anonymous said...

awesome, thanks!

Rocky said...

was this the MVP algorithm that kicked of the T de P?

Rocky

DrWes said...

Rocky-

The "MVP" (Minimum Ventricular Pacing) algorithm is a feature in dual-chamber pacemakers/defibrillators. This was a single-chamber VVIR device - hence MVP was not the cause of the Torsade de pointes noted in this case.