Supraventricular Tachycardia

This is an image of Bobby Julich, the most notable cyclist in the world to have been afflicted with supraventricular tachycardia. In 1996 Julich was in top racing form but suddenly withdrew from an Olympic Trial when his heartbeat reached an alarming level. He was treated with radiofrequency ablation and came back to pro racing to compete in that year's Vuelta a España. In 1998 he went on to finish third in the Tour de France.

Now we have an image of a not-so-notable cyclist:

That's me, crashing out in my first mountain bike race at Craighead Park. I don't share much with Bobby Julich, but I, too, am afflicted with supraventricular tachycardia.

In the spring of 2004 I was diagnosed with paroxysmal supraventricular tachycardia, but I have almost certainly had the condition much longer than that--perhaps for my entire life. What this seems to mean is that at unpredictable and irregular intervals the upper-chambers of my heart (the atria) speed up, putting them out-of-sync with the main pumping chambers (the ventricles). Usually, I don't notice this arrhythmia at all, but occasionally I can feel that my heart seems to be skipping beats or pounding irregularly.

In a normal heart, when the left atrium contracts, the mitral valve opens to allow blood into the left ventricle, which has just been emptied by its own contraction. In my heart the atrium apparently will sometimes contract at a time when the mitral valve is closed because the ventricle happens to be contracting at the same time. This causes the atrial blood to pound against the mitral valve and, over time, has caused me to develop mitral valve prolapse (a ballooning out of the valve). Interestingly, the "benefit" of mitral valve prolapse is that the sloppy valve acts as a shock absorber and makes the pounding of my heart less noticeable than it might be in someone with a normal heart.

The inefficient and asynchronous beating of my heart also means that sometimes the atria are not filled with blood when the ventricular valves open. Thus, the next ventricular heartbeat is "skipped." This causes an effective drop in blood pressure, and the body's feedback loop stimulates my ventricular heart-rate to increase in order to bring my blood pressure back up to its required level. So episodes of supraventricular tachycardia manifest themselves in an elevated and irregular heartbeat. If the heart-rate gets too high, the heart muscle does not have enough time to recover between beats. Contractions become weaker, resulting in exhaustion, dizziness, fainting, and (very rarely) death.

My desire to collect objective data about the functioning of my heart was a major factor in my decision to purchase a Garmin 305 GPS with heart-rate monitor. And after collecting several months of data during my time-trials, I have begun to have confidence in my understanding of my heart condition.

In the vast majority of my rides there is no evidence of any anomalous heart rhythm, but in a few there are episodes of arrhythmia of wildly varying length. In the first graph below I have superimposed the graph of my heart-rate on two rides of the same course at about the same average speed. During the "red" ride, my heart seems to have been beating normally throughout, with my maximum heart-rate peaking at about 158 at the tops of the steepest hills.

Comparison of Heart-rate During a Typical Ride and During One with Episodes of Arrhythmia
(Click on image to enlarge)

The "blue" ride, however, clearly has a section from mile 17 to mile 21 in which my heart-rate is about 15 beats-per-minute faster than expected. During this fifteen-minute period, my heart-rate spikes up to over 160 BPM (nearing, or slightly exceeding, the expected "maximum heart rate" for a person my age). I happened to glance at my heart-rate monitor during this section of the ride so I knew what was happening, but I felt perfectly fine. This is, of course, not particularly surprising. When my heart is in arrhythmia it is quite like having a four-cylinder car that is firing on only three cylinders. At low RPM's the engine runs sluggishly and may backfire; at high RPM's the engine seems to smooth out again.

Next we have a graph of my performance during my fastest-ever time trial on April 12th of this year. The green line shows the elevation, while the red line shows the associated heart-rate at that point. It was a cool day so there were no reliable heart data for the first three miles until I worked up a sweat and the chest-band was able to have good electrical conduction.

Data about Personal Record Ride
(Click on image to enlarge)

Note that from mile 3 until about mile 7 my heart-rate is consistently in the range of 140-150 BPM. This is consistent with a hard time-trial effort. Then, even though the route is descending and thus my heart-rate should be slowing because of the reduced effort, the data show a sudden upward blip of 15-20 BPM. For almost the whole rest of the ride my heart-rate stays above 150 BPM--greater than 95% of my maximal heart-rate by the standard calculation (Max HR = 220-age). Indeed, the average HR for the entire ride turned out to be 155 BPM -- an astonishing 95% to 98% of maximal HR, depending on one's method of calculation. Yet I felt solid, healthy, and energetic throughout the entire time trial. One can see in the data, by the way, that my heart occasionally tries to "reset" its rhythm. From mile 7 through 9, there are five separate downward blips of just the amount one might expect; and again at mile 27, in the midst of a fairly difficult little climb there is another downward blip of the right amount. In each case, however, there was so much adrenalin coursing through my system as I raced "the little demon" that my heart went right back into arrhythmia.

What can I conclude from all this? First, that I am blessed with a strong hemodynamic system so that minor cardiac inefficiency is not at all debilitating. Second, that if I can ever get out on a time trial on a really good day, and compete with the little demon without the handicap of arrhythmia, I should be able to shatter the record!

Update 7/29/2015

Today I came across a very useful and interesting article on cardiac arrhythmias in endurance athletes. If you have (or think you may have) such an arrhythmia, that article gives you a great dose of good guidance. As for me, I am still cycling 4,000 to 5,000 miles a year. This is enough to qualify me as a serious cyclist, but I'm not a competitive athlete. While I've completed a few centuries, my normal rides are in the 30-60 mile range (usually closer to 30).

For me, the best way to deal with SVT has been to completely avoid caffeine (coffee and tea, especially). That artificial surge of Adrenalin seems to have predisposed me to arrhythmia, and cutting it out entirely has really helped. I rarely have any problems at all (knock wood), but when something does knock my heatbeat off stride, I find that the Valsalva maneuver is pretty effective at restoring a normal rhythm. But the road ahead is never certain and contains different obstacles for everyone.

Update 1/28/2018

Here is another article that discusses the use of heart-rate monitors in athletes who suspect tachycardia. The gist of the article is that glitches in transmission of data tend to make athletic HRM devices unreliable in accurately detecting SVT. However, athletes with diagnosed SVT are advised to use these devices anyway. I guess the idea is that if you know you have SVT you should reduce exercise intensity whenever you see an exceptionally high heart rate. Better safe than sorry.

A more recent study suggests that newer HRM's are useful in detecting paroxysmal supraventricular tachycardia, but it was based on fewer subjects with fewer devices (Apple, Samsung, and Fitbit) during instances of induced SVT. It seemed a little less rigorous to me.