Scientists from the California Institute of
Technology (Caltech) have created images of the heart's muscular
layer that show, for the first time, the connection between the
configuration of those muscles and the way the human heart contracts.
More precisely, they showed that the muscular band--which wraps
around the inner chambers of the heart in a helix--is actually a sort
of twisting highway along which each contraction of the heart travels.
Their findings were published in the December issue of the American
Physiological Society journal, Heart and Circulatory Physiology.
Since the days of Leonardo da Vinci, observers of the human body have
known that the heart's beat is not a simple in-and-out movement--that
it has more than a little bit of a twist to it. "The heart twists to
push blood out the same way you twist a wet towel to wring water out
of it," explains Morteza Gharib, the principal investigator on the
study, and the Hans W. Liepmann Professor of Aeronautics and
professor of bioengineering in the Division of Engineering and
Applied Science at Caltech.
Some 50 years ago, anatomist Francisco Torrent-Guasp was the first to
show the helical configuration of the heart's myocardium--its
muscular middle layer, the one that contracts with each heart beat.
But what he and subsequent generations of scientists were unable to
do was to connect that myocardial band to the heart's function--to
prove that the helical shape is important to the effective beating of
the heart. Without that connection, physicians and scientists have
tended to look at the heart as "just a piece of meat," says Gharib.
Until now, that is. Using a technique pioneered by Han Wen and his
team at the National Institutes of Health, Gharib and his colleague
Abbas Nasiraei Moghaddam, a Caltech graduate and visitor in
bioengineering, were able to create some of the first dynamic images
of normal myocardium in action at the tissue level. "We tagged and
traced small tissue elements in the heart, and looked at them in
space, so we could see how they moved when the heart contracts,"
Gharib explains. "In this way, we were able to see where the maximum
physical contraction occurs in the heart and when--and to show that
it follows this intriguing helical loop."
With each beat of the heart, a wave of contraction starts at the
heart's apex--which, despite its name, is actually at the very bottom
of the heart--and then travels up through the myocardium. "The only
time the whole helix shows up in the images is at the end of systole,
which is when the heart is contracting," says Gharib. "This simple
band structure is akin to an engine behind the heart pumping action."
In addition to going a long way toward settling the decades-long
structure/function debate surrounding Torrent-Guasp's work, this
finding also has major implications for the surgical treatment of
heart disease, Gharib says. "It's going to change the way we repair
the heart," he explains. Knowing that the contractile wave travels
along the helical pathway--instead of occurring throughout the heart
all at once--has implications for which parts of the heart will be
most vulnerable to a surgeon's scalpel, for instance. "Seventy-five
percent of the function of the heart depends on this muscle," Gharib
says. "Surgeons now know what to cut and what not to cut. This will
help them to come up with new and more effective surgical procedures."
The work detailed in the paper, "Evidence for the existence of a
functional helical myocardial band," was supported by funding from
the Caltech MRI Center through a Discovery grant.
California Institute of Technology