Image: Boris Lyubner/Getty

The Design Bias of Heart Failure

Rose Eveleth

The lone artificial heart on the market fit 80 percent of men and only 20 percent of women. But the bias here is deeper than that.

Image: Boris Lyubner/Getty

There are lots of conversations about the lack of diversity in science and tech these days. But along with them, people constantly ask, "So what? Why does it matter?" There are lots of ways to answer that question, but perhaps the easiest way is this: because a homogenous team produces homogenous products for a very heterogeneous world.

This column explores the products, research programs, and conclusions that are made not because any designer or scientist or engineer sets out to discriminate, but because the "normal" user always looks exactly the same. The result is products and research that are biased by design.


In March of last year, Nemah Kahala needed a new heart. The mother of five kids had come from overseas to get treatment for her advanced heart disease, and she was in bad shape. When she arrived at the UCLA medical center, her heart was only pumping a trickle of blood. She required immediate surgery, and a short term replacement for the heart that was failing her.

Patients like Kahala are often fitted with an artificial heart for a few weeks while they wait for a biological one to become available. But her doctors quickly realized they had a problem: Kahala was a small woman, and the only whole artificial heart that was FDA approved for them to use was too big.

They quickly decided to apply for an FDA exemption to use a smaller heart, one that wasn't technically approved at the time. Their exemption was granted, and they placed a smaller artificial heart into her chest. The surgery went well, and the artificial heart held her over until she could get a biological transplant. A few weeks later, she was out of the hospital with a new heart.

"If you're in charge of changing the system, you have to know more than just 'women are dying.'"

But not everyone is so lucky. According to the CDC, heart failure impacts around 5 million Americans each year, and the same number of women and men die of heart disease each year. But despite striking men and women at similar rates, are some confusing disparities between men and women when it comes to heart transplants. Women are more likely to die while waiting for a heart transplant. And the artificial hearts available aren't designed to fit them.

Heart disease kills the same number of men and women in the United States, but when you look at heart transplants, you suddenly see a big gap. Eighty percent of heart transplant patients are men, and only twenty percent are women. Dr. Mario Deng, Kahala's cardiologist at UCLA Medical Center, wants to know why.

There is no single reason why women shouldn't be getting heart transplants at the roughly same rate as men. There are some factors we know about: Women tend to get heart disease later in life, and elderly patients aren't considered good candidates for heart transplants. But that can't explain everything, Deng said.

"Clearly there is a gender bias, the question is how does this gender bias happen," Deng told me. "What are the decision making processes and branching points where the female gender is not having the same access to care as the male?"

A patient with heart failure sees a lot of doctors, and has to make a lot of decisions. They see a general practitioner, a cardiologist, a heart failure specialist, a surgeon. At each of these points they are presented with information and have to make choices. Deng wants to know whether or not, at each of these points, doctors might be presenting information differently to men and women.

"At all these stages of—let's call it a heart failure patients 'career'—they make decisions towards a more proactive or less proactive path," he said. So a man who goes to a cardiologist might be pushed down a certain path that includes transplantation, while a woman might be pushed away from it.

Research has shown that doctors treat men and women differently. Men are more likely to be given pain medication than women are, while women are more likely to be given sedatives. One study found that women with cancer were more likely to be undertreated for pain than men are. A 2001 study found that women are "more likely to have their pain reports discounted as 'emotional' or 'psychogenic' and, therefore, 'not real.'" These same kinds of biases could be at work in heart disease, causing doctors to push women down a different route through their choose-your-own-heart-failure path. So perhaps doctors are subconsciously pushing women away from transplantation.

Then there's the small percent of women who do wind up on the path towards an artificial heart, like Kahala. Those women then face another challenge: the FDA-approved artificial heart is probably too big for them.

SynCardia's 70cc (left) and 50cc artificial hearts. Image: SynCardia

The most frequently used artificial heart is made by a company named SynCardia. In 1999, SynCardia's 70cc total artificial heart was approved in Europe, followed by the FDA in 2004 and Canada in 2005. And that 70cc heart fits "a majority of men and some women," according to the SynCardia site. "88 percent of the 70cc heart goes to men, and 12 percent goes to females," Don Isaacs, vice president of communications at SynCardia, told me.

SynCardia also makes a smaller 50cc heart, which can fit patients like Kahala whose bodies can't fit the larger 70cc heart, but using it requires a special exemption. And while the larger heart has been FDA approved since 2004, the 50cc heart, SynCardia only got FDA approval for a study on the smaller heart last year. It hasn't been approved for regular use. In order to use a smaller heart for a smaller patient, the doctor has to make their case to the FDA that they really truly need to use the heart to save a patient's life.

People often hold up this size disparity as a clear example of design bias in medical technology: How has it been 12 years since the larger heart was released, and there still isn't a smaller version approved for use?

Isaacs pointed out that artificial hearts were originally even bigger, 100cc, so they could be tested on animals. But a 100cc heart wouldn't fit most humans. So Syncardia worked to shrink it down to 70cc. "The first job was to get the 70cc study completed," he said, before SynCardia moved on to the 50cc. Fast forward 12 years and they're still working on the 50cc heart, trying to get it FDA approved. And Isaacs said that SynCardia is working on the 50cc heart as quickly as it can. He points the finger at the FDA's legendary sluggishness. "If someone wanted to manufacture and market an artificial heart, it would take them about 10 years to get approval," he said. But SynCardia didn't even submit the 50cc heart for FDA study until 2014.

There's also a question of scale. While 5 million Americans will suffer from heart failure each year, not all of them will need an artificial heart or heart transplant. According to Deng, about 10 percent of heart failure patients will develop advanced heart failure. Of that 10 percent, only 1 percent will get a heart transplant, and of that 1 percent, only 10 percent will need an artificial heart to bridge them between their failing heart and a new one. So when you get down to it, the market for artificial hearts is small.

SynCardia said that it has provided over 1580 implants since first gaining approval in Europe in 1999. In the grand scheme of medical devices, that is just not very many. Even compared to the demand for heart transplants in the United States, it's a drop in the bucket. (Plus, according to one study, women's hearts are more likely to be rejected by doctors for transplantation.)

And here we come back to the same statistic we started with: People who opt for and need an artificial heart are approximately 80 percent men, and 20 percent women.

For Syncardia, this feels like justification. Since the majority of people who need their product are men, it's okay that the company's product fits mostly men. In SynCardia's eyes, it's making a niche product to fit the demand it's seeing. And while the life and death of people should probably not be decided by the business decisions of a company, that's how things work. Yay capitalism.

How the artificial heart works.

But even women who don't need an artificial heart wind up with the short end of the stick on the transplant list. Every year, over 100 women in the United States die on the waiting list for a heart transplant. That's fewer overall than men, since more men are waiting for hearts, but women die at consistently higher rates than men while on the waitlist. And nobody knows why. Eileen Hsich, Associate Medical Director for Heart Transplants at the Cleveland Clinic, has spent the last few years trying to figure it out, but so far she's managed to rule out almost every variable she's tested: race, age, blood type, body mass, diabetes status, history of tobacco use, insurance, cardiac output and more.

All told, Hsich corrected for over 30 possible cofactors, and none of them explained the disparity. Something is causing women to die on that waiting list, and nobody knows what it is.

Hsich wants to pinpoint which women are at the highest risk, so they can be bumped up in the line before they die. But without knowing which women are at a higher risk she can't do much. "You can't lift all women up to the highest tier," she said, "you have to know something about who is the sickest and most at risk."

Hsich now has the ear of the United Network for Organ Sharing (UNOS), the private, non-profit organization that coordinates organ transplants in the US. She said that the group is interested in fixing this death gap, but can't fix it without knowing what, in particular, is broken. "If you're in charge of changing the system, you have to know more than just 'women are dying,'" Hsich told me. "You have to be able to say that it's a woman whose heart condition is this. You have to identify it."

Right now, they simply have no idea why women are dying more than men, and aside from Hsich very few researchers are trying to figure it out. That's frustrating for Hsich, but she said she's not going to give up.

"I am frustrated, but if I'm not doing it, who is?" she said. "If I give up that's it, there's really not anyone. I'm frustrated I don't have the answer and I may never have the answer, I think I'll get awfully close." In the meantime, women with heart failure are stuck, some with higher risk, and many with less options than their male counterparts.