Scientists have long suspected that smoking increased the risk that a transplanted heart would be rejected. Now they have a smoking gun.
And it doesn't matter who smokes, recipient or donor.
A new study conducted on rats provides the first direct evidence that cigarette smoke exposure before a heart transplant — by the donor, recipient, or both — accelerates the death of a transplanted heart. Tobacco smoke accelerates the immune system's rejection of the heart, reducing the odds of survival by somewhere between 33 and 57 percent.
"Our research shows that if a heart donor has been a habitual smoker, and you put that heart in a non-smoking recipient, that heart won't work; it will be rejected," said study team member Mandeep R. Mehra, professor of medicine at the Maryland School of Medicine. "This study shows beyond a shadow of a doubt how smoking affects transplantation."
The findings are detailed in the journal Circulation.
There are other risks at play, too.
"There are already many risk factors that physicians and surgeons must consider when they try to match a donor with a recipient," explained study leader Ashwani K. Khanna, at the University of Maryland School of Medicine. "This study makes clear that smoking in both the donor and the recipient should also become a part of the risk calculus in organ donation."
For the study, groups of donor and recipient rats were exposed to tobacco smoke while a control group of donors and recipients were not. The results:
- Transplanted hearts not exposed to tobacco were rejected an average of eight days after transplantation.
- Donor hearts exposed to cigarette smoke were rejected at five days, while recipient smoke exposure elicited rejection at four days.
- Hearts in which both the donor and recipient were exposed to tobacco smoke lasted just three days before the immune response began destroying the transplant.
Rats are thought to be a good analogue for what would happen in humans.
Other studies have hinted at the risk, but the magnitude of the problem proved surprising.
"The surprise in this study is the extent of the deleterious effects of smoking on the transplanted heart," said E. Albert Reece, vice president for medical affairs at the University of Maryland.
This research was funded by the University of Maryland Statewide Health Network and a Tobacco-Related Diseases Research Grant through the Maryland Cigarette Restitution Fund Program.