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XOIIO's avatar

So, how does a transplanted heart beat?

Asked by XOIIO (16862 points ) June 18th, 2014

Pretty simple, but I was wondering, since doctors can’t exactly reconnect nerves, when a heart is transplanted, how does it begin beating again? Does every heart transplant patient have a pacemaker to run their heart?

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14 Answers

thorninmud's avatar

The heart has its own pacemaker that acts independently of the rest of the nervous system. So the transplanted heart brings its own pacemaker along.

zenvelo's avatar

“lub-dub”

When it’s hooked up it gets a bit of an electric jolt to get started again.

gondwanalon's avatar

Once the transplanted heart is beating it will still need to be regulated to meet the bodiy’s varying needs throughout the day. For instance when the body is working the heart will need to be faster and while at rest the heart will need to beat slowly. Therefore an artificial pacemaker would be of great help.

gasman's avatar

Normally your heart has “pacemaker cells” with their own intrinsic rhythm to set the rate, by a process called spontaneous depolarization. The timing derives from steady leakage of ions across certain cell membranes by protein gates or channels embedded in the membrane. These cells are organized into a conducting system to maintain a normal sequence of events during each heartbeat. All of this pertains just as well to a transplanted heart whose control from “above” (i.e., brain & spinal cord) is via autonomic nerves, which get cut during transplantation.

The transplanted heart would still respond to hormones in blood, such as adrenalin.

From a Cleveland Clinic article on heart transplant:
Does the heart beat the same once the heart transplant takes place?
The donor heart comes with its own pacemaker and its own coronary artery supply. However, when the heart is removed from the body, the nervous system is disconnected. The heart continues to beat adequately, but without the external nerve supply. This is referred to as a denervated heart. In a small amount of cases, a pacemaker is needed after surgery to help the heart rate.

XOIIO's avatar

@gasman Huh, interesting.

JLeslie's avatar

That moment when they jolt the new heart and hope it is going to beat on its own is one of the tenses moments probably in the operating room. It is fascinating that the organ has it’s own ability to beat without the nerves connect. @gasman gave a great answer.

Unrelated, but related, I recently was listening to someone who is invloved with a lot of the research being done in spine injury and paralysis and they are realizing now that the spine almost has it’s own “brain.” There are studies going on where the spine is stimulated below the injury and the muscles are responding where the patient actually has some control to move a muscle on demand. The research is still in its infancy in my opinion, but the researcher I listened to said what they had always previously believed seems not to be true. It was fasinating to listen to her. I found this article to share with you.

SecondHandStoke's avatar

Heart menu> Restart.

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gasman's avatar

@JLeslie Remember that the term “central nervous system” includes spinal cord as well as brain. There is “gray matter” within the spinal cord, i.e., clusters of small neurons that do a lot of computation & signal processing before sending the final impulses down the axons to the muscles. Many reflexes (e.g., withdrawing your arm when you touch something hot) take place in the spinal cord before your brain ever gets wind of it. If you had to wait for the brain to make all the decisoins it would be too late.

JLeslie's avatar

@gasman I actually don’t remember learning anything like that. This woman involved with the research made it sound like brand new science. You make it sound like we have known for many years. I’m not sure what to make of that.

It reminds me of when I learned that when studies are done on medication before they are approved for market researches believed the results in woman weren’t valid ones because our hormones fluctuate so much. Idiots. I could rant on about that, but I’ll control myself.

gasman's avatar

@JLeslie Actually I hadn’t seen your article when I wrote my previous response. It looks like exciting research—electrically stimulating the spinal cord directly to produce useful muscle movements in spinal cord patients whose muscles are “disconnected” from the brain—using new technology combined with old knowledge, though it sounds like the spinal cord performed better than expected!

JLeslie's avatar

@gasman No problem. What I wonder is if the knowledge you spoke of has been around for many years, what took so long to do this sort of research?

gasman's avatar

The official title of publication: Altering spinal cord excitability enables voluntary movements after chronic complete paralysis in humans. Since I can’t read the article it’s not clear to me what the claimed results are, but this research probably couldn’t be done until the development of spinal cord stimulators, which have been in common clinical use (mainly for chronic pain) only in recent years.

JLeslie's avatar

@gasman Thanks so much for looking into it further. It’s fascinating.

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