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Had enough of Covid-19? Here's my first #tweetorial and I'll be looking at size-matching in heart transplantation.
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Size matching in heart transplantation is important. Ideally, you want a heart that big enough to generate an adequate cardiac output in the recipient. But not too big, or it won’t fit in the recipients chest.
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Donor and recipient weight have traditionally been compared to ensure the donor heart is an appropriate size for the recipient.
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This creates problems is a world where obesity is increasingly common. Heart size does not increase in parallel with weight gain. So the heart from an obese 100kg donor may be smaller than you were expecting for your 100kg recipient.
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And the problem is worse when a female donor heart is used in a male recipient. Believe it or not, it’s a biological fact that women have slightly smaller hearts than men, when adjusted for body size.
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Along comes Cardiac MRI. This allows heart size to be precisely measured. Using 1000’s of normal CMR scans, equations have been derived that allow you to accurately predict heart mass from 4 parameters.
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These PHM equations appear to be better at identifying ‘undersizing’ of heart transplants than the old-fashioned methods like weight alone. And we now know the price that recipients pay for undersizing - increased mortality.
7/n. (doi:10.1016/j.jchf.2013.09.005)
7/n. (doi:10.1016/j.jchf.2013.09.005)
Are these equations validated in a non-US population? We looked at 3400 normal CMR scans in the UK biobank study. The correlation between CMR mass and PHM was excellent (0.8). Much better than weight (0.68) or height (0.67).
8/n. (doi:10.1161/CIRCHEARTFAILURE.119.006362)
8/n. (doi:10.1161/CIRCHEARTFAILURE.119.006362)
We also wanted to know if the increased mortality associated with undersizing occurred in the U.K. So we looked in the U.K. transplant registry and found exactly the same pattern as the US.
9/n (doi:10.1111/ctr.14192)
9/n (doi:10.1111/ctr.14192)
So now we’re pretty certain that predicted heart mass equations are the optimal metric for size matching in heart transplantation.
10/n. (doi:10.1016/j.healun.2019.08.004)
10/n. (doi:10.1016/j.healun.2019.08.004)
But the maths is tough at 3am. Particularly when you just been woken up by a transplant co-ordinator. So we’ve developed an App to do the maths for you. And it’s FREE to download from the Apple store or Google play.
https://apps.apple.com/gb/app/heart-transplant-sizing-app/id1291915285
https://play.google.com/store/apps/details?id=com.wren.heartdonor
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https://apps.apple.com/gb/app/heart-transplant-sizing-app/id1291915285
https://play.google.com/store/apps/details?id=com.wren.heartdonor
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Thanks for reading. Now back to Covid-19....
