Statistics and Uncertainty

Hard life choices

If you’ve been reading this blog, you know that I have a heart aneurysm (if this is news to you, see my blog entry Heart Stuff). It is on the ascending part of my aorta, which is the largest artery in the body. I’ve had a recent CT scan to determine the size of the aneurysm, which was shown to be 4.7cm in diameter. It turns out that the size is important, because historically, aneurysms of greater than 5.5cm are recommended for surgery. In the past, smaller aneurysms are not treated immediately — they are observed, with scans every six months to one year to see if they are growing or not. If they are growing quickly, treatment is recommended. There are also some medical conditions that point to treatment at smaller sizes (Marfans Syndrome, Loeys-Dietz Syndrome, and other stuff that I don’t have).

Photo by Adrian Sulyok on Unsplash

Risk vs. Risk

To decide whether to operate or not, the basic idea is simple: is there a greater risk to waiting, or surgery? The risk of waiting is that the aneurysm might burst, which can be fatal. The risk of surgery is an adverse outcome, including stroke or death.

Risk of Waiting

There have been lots of studies which show that the risk of rupture or dissection increases with the size of the aneurysm. The risk of rupture for an aorta in the normal size range (<= 3.2cm) is almost zero. At more than 4.5 cm, the risk of rupture increases by more than 6300 times, but it is still low (0.3% per year). At a size that is greater than 6cm, the risk of rupture or dissection is approximately 14.1% per year.

American Cardiology Association

There is some controversy about these numbers. The American Cardiology Association and the American Heart Association have published new guidelines as of 2022 that suggest that intervention may be appropriate at smaller sizes. Another difficulty is that making measurements inside the body is not exact. Different types of scans can yield different results.

Risk of Surgery

The surgery to replace part of the ascending aorta is long and complicated. Practice makes perfect, my mom used to say. While hospitals are not perfect, their adverse outcome rate declines with the number of similar procedures performed each year. Most hospitals do less than 5 ascending aortic replacements in a year, and their mortality rates can be nearly 5%. For high volume surgical centers, their adverse outcome rates can be as low as 1%.

Just the Facts, Ma’am

The statistical comparison isn’t easy. 1% is less than 14.1%, so at higher diameters, it is safer to operate. But at 0.3% per year, the calculation is a little different. The one year risk is actually higher for surgery. But over five years, the rate of rupture rises to 1.5% for waiting, while the surgery risk stays at 1%. The reality is that both of these numbers are low. The chances that I can live without surgery or a rupture are pretty good. They are both great bets at a casino. But in a casino, you only lose some money. Here the stakes are higher.

Other factors

The logic that I’ve presented so far makes sense to me. There are other considerations that make things harder. There is no guarantee that a surgeon at a high volume center will take my case. I might be considered a riskier patient due to a number of possible conditions — size, diabetes, high blood pressure, and I’m a Cubs fan. They may advise me to wait until the aneurysm gets to a certain size, continuing to get scans every six months.

Psychological impact

I’m already anxious about this whole situation. Two weeks ago I felt just fine, and now I feel like I have a time bomb in my chest. Every little twinge gives me a start. I’m not sure that I want this feeling to continue. On the other hand, there’s no guarantee that if I have the surgery I won’t feel the same way, wondering if the new artificial blood vessel will hold.

The bottom line

My main interest is living the rest of my life with relative independence. I don’t want to lose my ability to think or to be a burden to others. I also don’t want to be afraid of picking up a bag of groceries or a small child. I’m unsure of how to proceed. I plan to talk to more experts, get more opinions, and do some more reading. If it does get larger, even then it feels like this will be a tough choice.