Custom Cardiology: A Virtual Heart for Every Patient

Illustration: James Archer; Hands: Getty Images

A poet might say that each human beings heart is a unique mystery. Those of us working in the brand new field of computational medicine, however, can now model each of those unique hearts with marvelous accuracy and reveal their secrets. In my laboratory at Johns Hopkins University, my team creates computer models to simulate individual patients hearts, which can help cardiologists carry out life-saving treatments. Such models may soon transform medicine, ushering in a new kind of personalized health care with radically improved outcomes.

Biomedical engineers have learned how to use numerical models to generate increasingly sophisticated virtual organs over the past decade, and rapid developments in cardiac simulation have made the virtual heart the most complete model of all. Its a complex replica, as it must mimic the hearts workings at the molecular scale, through the cellular scale, and up to the level of the whole organ, where muscle tissue expands and contracts with every heartbeat. Whats more, the modeling at these different scales must be tightly integrated to accurately render the constant feedback interactions that govern the functions of the heart.

Such models have already proved their value for basic cardiac research, allowing scientists to plug in experimental data and study what goes on in both normal and diseased hearts. Now, virtual hearts are poised to deliver breakthroughs at the bedside.

Starting with a patients MRI scans, specialists in computational cardiology can create a personalized model of the patients heart to study his or her unique ailment. Doctors can then poke and prod the computerized organ in ways that simply arent possible with a flesh-and-blood heart. With these models at their disposal, cardiologists should be able to improve therapies, minimize the invasiveness of diagnostic procedures, and reduce health-care costs. While this simulation-based medicine is still in the experimental stages, I believe upcoming clinical trials will show the real value of virtual hearts.

To grasp the vital importance of this technology, you have to understand todays standard of cardiac care. So imagine a patientlets call him Jimwho has survived a serious heart attack. It was a terrifying experience. He fell down, clutching his chest, fearing he was about to expire. But he was rushed to the emergency room, where doctors took swift action to restore the flow of oxygen-rich blood to his heart muscle. Jim is alivebut not quite as alive as he used to be. Some of the heart muscle, which was deprived of oxygen during the crisis, has died. The resulting patches of scar tissue can interfere with the electrical signals that propagate through the heart muscle, thus disrupting the contractions that should pump blood through the body in a steady rhythm.

If Jim develops an irregular heartbeat, called an arrhythmia, he may be in serious danger of cardiac arrest. His doctors must assess whether hes at high risk of developing this life-threatening condition and decide whether to implant a defibrillator in his chest. Just like external defibrillators used in ambulances and emergency rooms, an implanted device shocks the heart back into normal rhythm if arrhythmia develops, thus saving the patients life. To keep an at-risk patient like Jim from ending up in the ER, doctors may insert the internal device as a precautionary measure.

How can doctors judge whether or not to implant such a device in Jim? Its a big decision, because they dont want to needlessly put him through this invasive procedure and expose him to the possible complications that come with the defibrillator. Currently, cardiologists make their decision based on the patients ejection fractionthe proportion of blood that is pumped out of the heart with every beat. If this number is below 35 percent, then doctors advise the patient to undergo the implantation procedure. Lots of patients are getting implants based on this strategy, but in the first year after the procedure only 5 percent will go on to develop ventricular arrhythmias and receive a necessary shock. In other words, 20 devices are implanted for every one life saved.

Its clear that many patients are needlessly risking surgical complications, infections, and device breakdowns. The defibrillators arent perfect, and the electrodes that monitor the heart can malfunction, triggering an unnecessary shock. And a shock is a serious eventitcan feel like getting kicked in the chest by a horse. Patients sometimes lose consciousness, which could prove deadly if theyre driving, for example, or soaking in the tub. Most important, the ejection fraction isnt a good predictor of arrhythmia; it misses many at-risk patients. Many patients who dont fit the current criteria for an implanted defibrillator go on to die of sudden cardiac arrest, often in the prime of their lives.

My colleagues and I are now testing whether we can use patient-specific heart models to make better predictions of a persons risk of developing a life-threatening arrhythmia, and hence his or her need for an implanted defibrillator. To do that, we run simulations on the patients virtual heart to assess how prone it is to arrhythmia. We can do risky things to the virtual heart that physicians are reluctant to do to a live patientsuch as generate small electric pulses in different locations and then watch to see whether arrhythmia develops.

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Custom Cardiology: A Virtual Heart for Every Patient