Gas station without pumps

2021 November 10

PVC: Premature Ventricular Contraction

Filed under: Circuits course — gasstationwithoutpumps @ 14:05
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This fall, when I went to my doctor for my standard annual physical, she thought my heartbeat sounded a bit strange, so she ordered a 12-lead ECG and an echocardiogram.  The imaging report from the cardiologist told me some things I already knew from the tests done for Project Baseline almost 3 years ago—namely that there was some sclerosis on the aortic valve, but no stenosis. There were a couple of new things reported, though: frequent premature ventricular contractions (PVCs) and mild concentric hypertrophy of the left ventricle.

I looked up what PVCs are and how they are diagnosed, since they were reported on both the ECG report and the echocardiogram report. PVCs are extra contractions of the ventricle, triggered by something in the ventricle rather than the sinus rhythm from the sinoatrial node.  The diagnosis on the ECG is pretty easy, as there is no P spike from the contraction of the atrium, and R spike travels in a different direction from a normal beat—radiating from the different initiation point.  That sounded like something I could see with my home-built ECG that uses just an MCP6004 op-amp chip, a few discrete passive parts, and a Teensy LC running PteroDAQ.  So I set up the ECG and recorded for about 5½ minutes on Lead I, then for about 4⅓ minutes on Lead II.

I saw 37 beats that looked odd in the Lead I recording, or about once every 9 seconds, which certainly qualifies as “frequent”.

10s-Lead-I-2021-Nov-10

Here is a 10-second stretch of Lead I, showing both normal beats and two of the PVCs.

normal-Lead-I-2021-Nov-10

Here is a normal beat and part of a second normal beat, as a detail of the 10-second interval. I’ve aligned the R spike to be at about 400 ms.

PVC-Lead-I-2021-Nov-10

Here is one of the PVCs—the first from the 10-second section shown above. I’ve aligned the R spike to be at about 400ms.

The PVC is clearly missing the P spike, the R spike suggests an orientation for the depolarization wave almost at right angles to Lead I, and the T spike is larger than usual.  I have not seen (or at least not noticed) this waveform in my years of playing with my home ECG, so I think that the PVCs have developed in just the past 2 years (they were not mentioned on my stress ECG and echocardiogram reports from Project Baseline in December 2018, and they would be hard to miss, so I don’t think I had them then).

Formerly, both my Lead I and Lead II recordings looked like the canonical PQRST complex that one sees in popular representations of heartbeats, but now my Lead II shows a different pattern, indicating that the direction of the depolarization wave has changed.

normal-Lead-II-2021-Nov-10

Here is a normal pulse from Lead II. This is not what I used to see, so I think that even the normal depolarization waves are traveling in a different direction than they used to.

So I do have something new going on with my heart, even though I am not experiencing any symptoms from it. From what I’ve been able to tell from reading on the web, PVCs are common and not dangerous—unless one gets other symptoms.

The “mild concentric left ventricular hypertrophy” in the imaging report might explain the change in the direction of the depolarization wave, but I don’t understand the cause of the hypertrophy. What I’ve found online indicates that high blood pressure is a common cause for hypertrophy, but I don’t have high blood pressure.  The analysis of the echocardiogram imaging report was “Your heart ultrasound is essentially normal with no significant abnormalities.”

So there doesn’t seem to be anything to be concerned about with these changes in my heart, but I suspect that my doctor will want to monitor the changes on a periodic basis.

4 Comments »

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