New MIT research on the human heartbeat could lead to less expensive, noninvasive ways to diagnose one form of heart disease.
The work, reported in the October 2 issue of Nature, also resolves a long-standing debate among scientists about the dynamics of the heartbeat.
Contrary to perceptions in the general public, it is an established fact that the human heartbeat, or more specifically, the heart rate, is irregular. The time between each beat of the heart varies by a millisecond here, two there. Many scientists have thought this variability is random. The new MIT work, however, shows that the heart rate actually follows a subtle structure, albeit a complicated one.
This is important because "if there's a structure behind it, and if we can understand that structure, we can learn more about the heart and heart disease," said Dr. Chi-Sang Poon, lead author of the Nature article and a principal research scientist in the Harvard-MIT Division of Health Sciences and Technology.
A finding by the MIT team which is key to the potential diagnosis of heart disease is that individuals suffering from congestive heart failure (CHF) have significantly different heart rate "structures" than people with healthy hearts. Consequently, with further development, the technique that the team used to glean these results could become an aid to diagnosing CHF, which affects more than two million Americans.
Because the technique is essentially a computer program that analyzes the electrocardiograms (EKGs) of patients -- data that are already available -- it does not involve invasive procedures. It could also be very quick and relatively inexpensive, said Dr. Poon.
Using the new technique, the researchers found that the human heart rate is chaotic. Unlike its popular everyday definition, chaos is a scientific phenomenon in which seemingly random, disorderly data actually follow a subtle structure. The phenomenon has been found in many areas of science, from the weather (as established by Professor Emeritus Edward N. Lorenz of earth, atmospheric and planetary sciences) to the orbits of asteroids (as established by Professor Jack Wisdom of the same department).
Whether or not the human heart rate is chaotic has been hotly debated within the scientific community for many years. That's because "until now, there has really been no reliable way of detecting chaotic dynamics in the system," Dr. Poon said.
Enter the technique that he and colleagues reported in the May 16, 1996 issue of Nature (see MIT Tech Talk, June 5, 1996). For the work reported in the current Nature paper, Dr. Poon and his coauthor, Christopher K. Merrill (SB '96), applied the technique to the human heart rate. They used it to analyze heart rate data collected by Dr. Ary Goldberger of Boston's Beth Israel Deaconess Medical Center from eight healthy individuals and 11 suffering from CHF.
The result: "we've definitively shown that the healthy heart beat is chaotic," Dr. Poon said. "Chaos is part of the normal operation of the circulatory system." In contrast, the researchers found that the heart rates of CHF patients "become more regular and less chaotic. Their heartrates appear to be more 'behaved' than those of healthy individuals," he said.
"These findings suggest that cardiac chaos is prevalent in the healthy heart, and a decrease in such chaos may be indicative of CHF," Dr. Poon and Mr. Merrill concluded in their Nature paper:
Dr. Poon, who has filed for a US patent on the technique used in the current work, is working to refine it as a diagnostic aid for CHF.
The work was sponsored by the National Heart, Lung and Blood Institute, the National Science Foundation and the Office of Naval Research.
A version of this article appeared in MIT Tech Talk on October 8, 1997.