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A Revolution in Heart Transplants

April 17, 2020

A ‘Cool’ Way to Transport or Not? 

Since their successful conception in 1967 by Dr. Christiaan Barnard, heart transplants have been a staple in the transplant world. They have provided many individuals with end stage cardiomyopathy (weakening of the heart muscles), heart valve disease, coronary artery disease, or other cardiovascular diseases a second chance at life. However, even as medical technology rapidly progressed over the years, one part of the heart transplant procedure remained relatively the same: the process of transporting a donor heart.

Traditionally, once a donor heart becomes available, it is removed from the donor’s body, sealed in a plastic bag, and then placed in an ice cooler. The cooler is then transported to the hospital where the heart transplant surgery will occur. While this might be the most common method for transportation, it is definitely not the most effective. On average, 8 out of 10 donor hearts don’t make it to transplant surgery. This can be due to the limited amount of time a heart can remain outside of the body, formally known as ischemic time. A heart can ideally last outside of the body for 4-6 hours. If the time goes longer than that, then the ice surrounding the heart can begin to cause irreversible damage to the heart cells, leaving it unable to be restarted. Because of this short transport time period and possibility of cellular damage, it’s very difficult to transport a heart successfully, even if the donor is a perfect match. In 2017 alone, only 3,244 hearts were transplanted when an estimated 100,000 patients needed a new heart.  

However, a new solution to this problem is currently in the works thanks to a company called Transmedics.

Transmedics: Heart in a Box

In the early 2010s, Transmedics brought a new method of donor heart transportation to the table, and it came in the form of a mechanical box. Heart in a Box or the Organ Care System (OSC) Heart served a radical idea: what if we could keep a heart beating during transport? 

And they accomplished just that! Once a donor’s heart becomes available for transport, it is placed inside the (OSC) Heart, where doctors will hook tubes into the aorta (the main artery that pumps oxygenated blood to the rest of the body) and the pulmonary vein (which transfers oxygenated blood from the lungs to the heart). These tubes are used to pump oxygenated blood sourced from the donor through the heart by mimicking the changes in pressures inside the left ventricle and left atria. From this process, the heart receives the necessary nutrients and oxygen needed to function properly, meaning that it can basically be kept alive outside of the body thus eliminating ischemic time. The OSC even comes with a portable tablet that monitors the vitals of the heart (such as rhythm and heartbeat) and allows for direct changes to be made to pump flow rate or nutrient levels to keep the heart functioning properly throughout the transport process.

With the heart kept alive and beating, the time limit for transport is vastly increased. Current trials have shown that with OSC, donor hearts can remain viable for up to 12 hours, double what could be achieved with the cooler! With the heart being constantly monitored to maintain proper function instead of being iced and not beating, it also eases the process of restarting the heart in the recipient’s body. These changes could mean huge advancements in the number of patients that successfully receive a donor heart for transplant. The OSC Heart is still undergoing FDA clinical trials to prove its safety and benefit to heart transplant recipients before it becomes a wide scale method of transport, but so far many transplants that have occurred with the device have been successful. Transmedics is even branching out to using similar OSC for other organ transplants, such as lungs and kidneys. As of now, we’re on track for a brighter future for transportation of donor organs.  

The Heart Beats On

The story of Transmedics reminds us of a valuable lesson: just because a medical procedure or device is widespread doesn’t mean that it is most effective. Current methodology needs to be questioned to look for ways of improvement. Nothing is perfect. Sometimes creativity and innovation are needed to cause a paradigm shift that can completely change how the world handles a medical issue. Never stop looking for scientific improvement! You never know if your idea might end up saving someone’s life.

 

Citations

Breining, Greg. “Heart in a Box.” Medical School – University of Minnesota, 28 Mar. 2017, med.umn.edu/news-events/medical-bulletin/heart-box.

Breining, Greg. “Transplant Transport.” Legacy, 11 Sept. 2018, discoverymag.umn.edu/stories/transplant-transport.

“Heart Transplant.” Mayo Clinic, Mayo Foundation for Medical Education and Research, 16 Nov. 2019, www.mayoclinic.org/tests-procedures/heart-transplant/about/pac-20384750.

“OCS Heart for Patients and Families.” Transmedics, www.transmedics.com/ocs-heart/.

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About Author

Lindsay is a undergraduate Computational Media student at Georgia Tech. She loves reviewing the history of medicine and science and making connections to the present-day. In her free time, she loves drawing cartoons and painting.

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  Timothy Durham was convicted of rape when a test showed his DNA genotype matched the DNA recovered from the crime scene. Eye witnesses testified that Durham was in a different state at the time of the incident, but he wasn’t exonerated from his 3000 year sentence until follow up DNA analysis showed that the preliminary forensic analysis used in the trial was misinterpreted (Thomas et al.). DNA testing serves an invaluable part in our criminal justice system, but it comes with complications and bias that can lead to wrongful convictions and misinformed juries.  

Background:

Forensic genetics aims to identify the origin of a biological sample. It can be traced back to Karl Landsteiner who discovered human ABO blood groups. With blood groups, suspects could be eliminated based on their blood type. For example, if a suspect had type A blood and there was type B blood left at the scene by the perpetrator, the investigators could rule out the suspect. Unfortunately, the reverse didn’t work. If the suspect and perpetrator both had the same blood type, it can’t be concluded that the suspect was guilty. Blood identifiers evolved into 8 distinct categories which improved the ability to eliminate suspects, but could only conclude that (if the system matched) it might be the perpetrator or this person might be related to the perpetrator (Jobling and Gill). The field evolved in the 1980s with the discovery of Minisatellites, lines of repetitive DNA that don’t encode proteins. Minisatellite patterns in DNA create what we know today as the DNA fingerprint, and it has a much higher accuracy rate than previous methods (Augustyn et al.). Around the same time, a breakthrough for victims of sexual assault was discovered. In the case of assault, bodily fluids of both the victim and the assaulter can get mixed. A process called differential lysis was created which could selectively increase the concentration of sperm in a fluid sample thereby allowing for accurate DNA testing (Jobling and Gill). Forensics evolved to use single-locus probe testing after several years because of its ease of interpretation. It looked at specific minisatellites that had high variability between subjects. This was the first DNA-based method to be used in a criminal investigation. Two murder homicides from several years apart were connected using DNA evidence. The evidence was then used to exonerate an innocent man, and the guilty party was found when he tried to evade mandatory DNA testing for all men in the small town. His guilt was then reinforced when the DNA profiles matched, and he gave a confession (Jobling and Gill). Finding DNA at a crime scene doesn’t guarantee that you’ll find a murderer. There are issues with non-pure samples and limited samples that make DNA work difficult, and accreditation of facilities and new techniques and take time (Jobling and Gill).  

Subjectivity of DNA Interpretation:

In a 2009 publication, the National Academy of Science discusses the possibility for subjective influence in lab based forensics. The interpretation bias happens in complex cases where, for example, there could be a mixture of DNA. A study published in 2011 looked specifically at this issue. A gang rape happened in Georgia, and the mixture in DNA from the case was used to prosecute one suspect after another suspect took a plea bargain to testify against him. With DNA mixtures, there are three possible conclusions: suspect excluded, suspect cannot be excluded, and inconclusive. If the suspect is excluded, it means that there’s little to no possibility that his DNA is part of the sample. If the suspect cannot be excluded, it means that there’s a possibility that his DNA is part of the sample. In the trial, the DNA examiners who knew the context of the case concluded that the suspect being prosecuted could not be excluded. The 2011 study gave the DNA evidence from this case and the DNA profiles of the suspects to 17 forensic examiners. These examiners had no context of the case, and they all worked independently. Of the 17, only 1 came to the same conclusion (suspect cannot be excluded) as the examiners who knew the context of the case. Twelve of the 17 concluded that the suspect who was prosecuted and convicted had no relation to the DNA found in the sample. Not only does this show that subjectivity occurs due to the context of the case, but the 17 examiners came up with different findings based on their past experiences meaning that not all DNA analysis is objective. Some organizations like the Scientific Working Group on DNA Analysis Methods say that quantitative statistical evidence should be presented with every categorical conclusion, but the US doesn’t require this (Dror and Hampikian).

False Positives:

There are two categories that cause wrongful identification in a DNA report: coincidental matches and false positives. Coincidental matches are DNA matches between two unrelated people. The probability of these matches is about 1 to 500,000 for white individuals and about 1 to 350,000 for black individuals. This small probability of coincidental matches makes people feel confident in DNA evidence. False positives, on the other hand, are matches between DNA and test DNA that result from issues in the forensics lab. There have been multiple cases of forensics labs accidentally switching victim and suspected rapist DNA which lead to convictions that were later overturned when the lab realized the error. There are also cases of misreading or misunderstanding a sample. In a case from 1993, a man was convicted of rape because someone interpreted a mixed sample of victim and perpetrator DNA as an individual sample. The conviction was again overturned. To prevent false convictions, retesting DNA is allowed, but it’s not an efficient solution. Many people are pushing for statistical information on the probability of false positives, so that the jurors can make accurate judgements based on DNA evidence (Thomas et al.).  

Conclusion:

DNA analysis is a useful tool for the criminal justice system, but subjectivity can be an issue in forensic testing. To combat wrongful convictions, there are organizations like The Innocence Project who use DNA testing to free the innocent, but reformed forensic testing standards should be put in place to prevent subjectivity and to ensure juries are correctly informed during trials. https://www.innocenceproject.org/    

Citation:

Augustyn , Adam, et al. “DNA Finerprinting.” Encyclopedia Britannica , 26 Apr. 2018, www.britannica.com/science/DNA-fingerprinting#ref153186. Dror, Itiel E., and Greg Hampikian. “Subjectivity and Bias in Forensic DNA Mixture Interpretation.” Science & Justice, vol. 51, no. 4, 2011, pp. 204–208., doi:10.1016/j.scijus.2011.08.004. Jobling, Mark A., and Peter Gill. “Encoded Evidence: DNA in Forensic Analysis.” Nature Reviews: Genetics, vol. 5, no. 10, Oct. 2004, pp. 739–751., doi:10.1038/nrg1455. Thompson, William C, et al. “How the Probability of a False Positive Affects the Value of DNA Evidence.” Journal of Forensic Sciences, vol. 48, no. 1, Jan. 2003, pp. 1–8., doi:10.1520/jfs2001171.