Technical FAQ: Questions about blood flow reduction post-ablation and SVT

VeloNews technical expert and author of the Haywire Heart Lennard Zinn answers questions about side effects of ablation procedures, and also Supraventricular Tachycardia.

Get access to everything we publish when you join VeloNews or Outside+.

Have a question for Lennard? Please email him at to be included in Technical FAQ.

Dear Lennard,
I don’t know if you have run across this in your research, but I am curious about the potential for a minor constriction in the femoral vein(s) after an ablation procedure. I have looked into the clinical literature and haven’t seen anything about this.

My hypothesis is that puncturing the vein, inserting a catheter, then re-sealing the vein would likely cause some fibrous scar tissue to form at the puncture site. This could potentially restrict return blood flow from the legs during heavy exercise.

I raise this question because I have gone through two ablation procedures. Both were mostly initially successful in eliminating my atrial flutter. After each one, I slowly returned to my exercise routine and found that I had lost a bit of endurance in my legs. I grow tired and start to feel “heavy legs,” but my heart rate doesn’t increase as much as it did before my procedure. One explanation for this would be reduced circulation in the legs.

If there is such an effect, I would guess that this would take a little bit of power out of even the best-trained athlete. And I would not be surprised if Zdenek Stybar will no longer be the incredibly strong rider he has been up until now.

As an aside, I am a biomedical engineer and have studied arrhythmias for 30 years. I am very impressed by your ability to translate rather complicated aspects of cardiac electrophysiology to your readers!
— Jamey

Elia Viviani, like Diego Ulissi above, underwent an ablation procedure. Photo James Startt

Dear Jamey,
I asked Dr. John Mandrola, co-author of The Haywire Heart, about this. He said, “There is always a tiny bit of fibrosis that occurs on top of the vessels that we go into in the veins. After 24 years of doing it, I’ve never known anyone to have a clinical problem from it. Usually, the fibrosis fades away. I have seen people get clots in the deep veins after a procedure, but these are not subtle and occur in the days to weeks after the procedure.”

Let’s hope that Stybar had a simple ablation of something like Paroxysmal Supraventricular Tachycardia (PSVT), that it went well and also caused no flow restriction in his femoral vein(s), and that he is able to return to being “the incredibly strong rider he has been up until now.”
― Lennard

Dear Lennard,
I am a recreational racing cyclist, and I just turned 66 last week.

Last summer, I had a situation in which my HR, which already is somewhat high at about 190 with a resting HR of around 45-50 bpm, spiked to over 210. I had done a hard effort, but then stopped with a group to wait for some folks. We started again, but within about a mile I noted that my HR (which had gone down during the brief rest) was now over 210. I stopped riding, but nothing happened. Being in the middle of nowhere with few options, I decided to continue at a reduced pace until I got to the next rest stop, which was about 15 miles. Through this period, which was about an hour, my HR stayed pegged at 210 and only returned (suddenly) to normal after about 20 minutes at the rest stop.

I got a ride back to my car from there, then went to the ER where they did two EKGs and said if I hadn’t told them, they wouldn’t have known anything was wrong. The following Monday, I went to a cardiologist who also found nothing wrong, but subsequently did two heart ultrasounds and a treadmill stress test. Nada. He opined (as did another doctor friend) that I’d had a supraventricular tachycardia (SVT) and gave me some methods to stop it should it recur.

I was led to believe that this was scary but not life-threatening. I took it easy for a while, but I’m pretty much back to normal activity and intensity now, and I have been for some time. However, based on your recent article, I’m now wondering whether I should be doing this, as it seems like SVTs may be more serious than I understood. I’ve not had a recurrence, but your article in VeloNews has left me a bit concerned. I also read your book on this subject, and again came away (perhaps wrongly) that an SVT would likely not kill me.

Did I misunderstand?
— John

Dear John,
That is accurate; an SVT would likely not kill you, and I attempted to explain why a few weeks ago in this column.

While SVT is generally not life-threatening, studies suggest that the likelihood of developing AFib (atrial fibrillation) is higher in a person with SVT than it is in the general population. The stress on the heart is higher when it is in SVT than when it is in sinus rhythm, which could increase propensity toward AFib. Perhaps similarly, the extra stress on the heart caused by sleep apnea greatly increases the likelihood of developing AFib. People with untreated sleep apnea can stop breathing and wake up (often without realizing it) tens of thousands of times per night as their fight or flight mechanism is repeatedly activated to keep them from dying of asphyxiation.

It is much better to not have AFib than it is to have it. In addition to slowing you down on the bike, it can potentially result in having to get cardioverted out of AFib in the emergency room, and/or in either ablation or a firm recommendation from a doctor to go on blood anticoagulant medication to reduce stroke risk (from a clot that might form on the surface of blood jiggling in a disorganized way in the atria of the heart).

All this is to say that, if I were you, I would endeavor to keep your heart from going into SVT. I have atrial arrhythmia, and, partly in order to reduce my chances of developing AFib, I seek out outdoor activities I enjoy that I can do without putting my heart into arrhythmia. For the same reason of reducing my chances of developing AFib, I also endeavor to not go into sleep apnea, something I seem to have developed in the past few years. To do that while avoiding a CPAP machine, I sew a pocket on the back of any T-shirt or pajama top I sleep in and put two tennis balls in it when I go to bed. That prevents me from sleeping on my back, which in turn prevents my tongue from falling back and blocking my airway, bringing on sleep apnea.

I’m not saying that there is anything wrong with your current regimen. If you have only had one occurrence, there is no evidence to say unequivocally that it will happen again while riding. Your approach of taking it easy for a while followed by resuming your normal activity level after not having experienced a recurrence is not nonsensical.

If, however, SVT episodes do recur while riding, I would recommend paying close attention to what exactly triggers them and avoid those triggers as much as you can.
― Lennard

Lennard Zinn, our longtime technical writer, joined VeloNews in 1987. He is also a custom frame builder ( and purveyor of non-custom huge bikes (, a former U.S. national team rider, co-author of The Haywire Heart,” and author of many bicycle books including Zinn and the Art of Road Bike Maintenance,”DVD, as well as Zinn and the Art of Triathlon Bikesand Zinn’s Cycling Primer: Maintenance Tips and Skill Building for Cyclists.” He holds a bachelor’s in physics from Colorado College.

Follow @lennardzinn on Twitter.