Digital Pulse Wave Analysis Offers
Non-Invasive Early Heart Risk Assessment
By August West
Contributing Writer
Central Aortic Systolic Pressure
(CASP) is one of the most powerful early predictors of cardiovascular risk. New digital pulse wave analysis technology is putting this
valuable test in the hands of prevention-focused primary care doctors.
Safe and non-invasive, pulse wave analysis applies the principles of sonar to
assess the pliability of the vascular tree, including the major central vessels
as well as the small peripheral vessels. Central aortic vascular compliance, or
lack thereof, is a key indicator of vascular health or lack thereof.
"This is a really great test for
people who are seemingly without symptoms, but who are about to have lots of
disease," explained J. Joseph Prendergast, MD, director of the Endocrine
Metabolic Medical Center, Palo Alto, CA. Dr. Prendergast is among the pioneers
of pulse wave analysis, particularly as it applies to the prevention of heart
disease among people with diabetes.
He noted that diabetics tend to show
a pattern of atherosclerosis distinct from what one typically sees in
non-diabetic CVD. "Diabetics get more long artery atherosclerosis, whereas in
non-diabetics, you tend to see the plaque only in smaller branches, and at the
points where the vessels branch off." Pulse wave analysis opens a window into
the condition of the long vessels.
Measuring the Bounce
Arterial pulse wave analysis has been available as a research tool for about ten years,
and has just begun to enter clinical practice. In essence, it measures
reflection of pulse waves off the walls of the aorta and the peripheral
vessels. As the pulse travels down the aortic trunk, it hits smaller
arteries and is reflected back. This bounce-back wave runs headlong into the
oncoming pressure wave from the subsequent heartbeat, augmenting pressure on
the vessel walls.
The general principle is that higher
pulse reflection scores indicate stiffer, more plaque-bound vessels, and
therefore greater imminent risk of cardiovascular events. "It's like dropping a ping-pong ball on a carpeted floor
versus a hard marble floor. The harder surface will give a stronger bounce,
while the carpet will absorb the force."
Dr. Prendergast said
state-of-the-art technology allows assessment of, "all sorts of reflections and
pressure subtleties." But from a practical viewpoint, you really only need to
look at two key measures: the central aortic pulse (CASP) reflection, which
shows the flexibility of the aorta and, by extension, the major vessels, and
the pulse reflection in the small arteries. "The small vessels can tell you
about metabolic syndrome. But the bigger vessels tell you about imminent
cardiovascular risk."
In a certain sense, pulse wave
analysis is a modern elaboration of the ancient art of pulse diagnosis
developed thousands of years ago, and still used by practitioners of
traditional Chinese and traditional Indian medicine. TCM and Ayurvedic
practitioners will spend considerable time evaluating the pulses, sensing in
them subtle indicators of health or disease.
The new pulse wave technology is
based on a similar premise that the health of the vasculature, indicated by its
degree of elasticity, is a key indicator of overall physical health. Pulse wave
analysis quantifies the signals and opens up vast new dimensions of study in
this domain.
"I Had to Re-Think Everything"
Dr. Prendergast's interest in this
field grew out of his effort to meet his own health challenges. Back in the 1970s,
at the age of 37, he was diagnosed with advanced atherosclerosis, though he was
asymptomatic and had fairly normal serum cholesterol. Given that his father had
a stroke at age 42, he became very concerned.
Faced with a serious health threat,
he realized the limitations of his medical knowledge. "Medicine, at that time,
really had nothing for me. I had to re-think everything. I knew I couldn't rely
just on pharmaceuticals," said Dr. Prendergast, who today is in his 70s and
very healthy.
A friend and colleague, Victor Dzau,
MD, now chancellor for health affairs at Duke University, introduced Dr.
Prendergast to L-arginine, an amino acid which, when taken supplementally, can
increase endothelial nitric oxide release. Many researchers and clinicians believe
that when used properly, arginine improves vascular health and reduces CV risk.
Arginine quickly became a cornerstone not only in Dr. Prendergast's own
personal heart health regimen, but also in his treatment protocols for patients
at risk.
He began looking at pulse wave
analysis after meeting Stanford University researchers who were the emerging
technology to detect early signs of Alzheimer's disease, diabetes and CVD. He
saw in it the potential to be a useful guide in determining who really needs
arginine therapy. He is currently consulting with CardioGrade, LLC
(www.cardiograde.com), a California company focused on bringing this emerging
technology into wider clinical use.
Looking Upstream
Conventional treatment of
cardiovascular disease, a complex multi-system aggregation of dysfunction, is
often guided by fairly simplistic measurements: serum LDL, HDL and Triglyceride
levels, and blood pressure as measured by sphygmomanometer cuff readings at the
brachial artery.
Dr. Prendergast sees brachial artery
pressure measurement as convenient but primitive. Over-reliance on it (brachial aartery pressure) is one
reason that anti-hypertensive therapy often fails to prevent life-threatening
CV events. "When you put the cuff on someone's arm, all you're really looking
at is the download pressure back into the hands. All it really tells you is the
condition of the vessels in the wrist. You need to go upstream into the central
vessels." He added that many drugs will lower brachial pressure but not reduce
risk.
Pulse wave devices also take readings
from the wrist, but there is no arterial occlusion as with a standard pressure
cuff. "The wave forms of the pulse tell you what's going on in the aorta and
the other vessels," he said. It gives a very different type of information than
standard BP measurements.
The discrepancy between the brachial
arteries and the central aortic trunk was underscored in the Conduit Artery
Function Evaluation (CAFÉ) study. Researchers compared beta-blockers plus
diuretics versus calcium-channel blockers in hypertensive, high-risk people,
and found that while both treatments gave similar and significant reductions in
standard brachial artery pressure, the central aortic systolic and pulse
pressures were substantially lower in patients on calcium-channel blockers
(Williams B, et al. Circulation. 2006; 113(6): 1213-25).
"You can get similar pressures in
the arm but very different pressures in the central arteries, depending on what
the drugs do to the wave reflections," explained Bryan Williams, MD, of the
University of Leicester, UK, who led the CAFÉ study. "Beta blockers and
diuretics, which we use very commonly, while they lower blood pressure and
reduce risk, are less effective…in preventing the reflected wave from coming
back at the wrong time. You get a slightly higher central pressure with those
drugs than you do with amlodipine and perindopril."
Dr. Williams had high praise for
pulse wave analysis, which in the CAFÉ trial was done with the Spygmocor system
(www.atcormedical.com). "I think this type of technology is going to be
increasingly used in clinical trials because it gives us information that we
haven't had before. It can be easily used and can produce very effective
results."
A Surge of Research
Pulse wave analysis has attracted
vigorous research interest of late, with well over 50 studies published just in
the last 6 months.
Investigators at Fukuoka University
Hospital, Japan showed a strong correlation between aortic augmentation index,
a type of pulse wave measurement, and severity of atheromatous plaques in a
cohort of 96 patients with paroxysmal atrial fibrillation. High augmentation
scores correlated with age, plasma LDL, aortic stiffness scores, and other risk
indicators, leading the researchers to conclude that this represents, "a novel
tool for determining the severity of central aortic atheromatous lesions."
(Sako H, et al. Circ J. 2009; Apr 16; Epub ahead of print).
Augmentation index and central
aortic pressure also correlates with smoking, according to researchers at
Dokkyo Medical University, Japan. They looked at 443 otherwise healthy
normotensive men, and found that the augmentation index was markedly higher in
current smokers compared with never- and former- smokers. Central systolic
pressure was higher in current and former smokers compared with lifelong
non-smokers. Interestingly, brachial systolic pressure was not significantly
different among these groups (Minami J, et al. Am J Hypertens. 2009; Mar 26,
epub ahead of print).
The good news is that most aortic
pressure risk indicators will normalize when people quit smoking. A multicenter
Portuguese study looking at pulse wave patterns in 71 long-term heavy smokers
showed that after 6 months, those who quit showed significant reductions in
peripheral systolic pressure, augmentation index, pulse wave velocity and other
risk indicators compared with the men who continued smoking (Polonia J, et al.
Blood Press Monit. 2009; 14 (2): 69-75)
Dr. Prendergast noted that because
pulse wave analysis is noninvasive, it is an excellent office-based tool for
tracking patients' response to treatment over time. In his clinic, the therapy
revolves around diet and lifestyle change, as well as intensive use of
nutraceuticals like L-arginine, vitamin D, resveratrol, and others. "People
still need to change their diets. You cannot totally over-ride a bad diet with
arginine or any other supplements," he said.
Currently, digital pulse wave
analysis systems cost roughly $10,000, said Dr. Prendergast. But he expects the
prices to come down as the technology improves and gains in popularity.
Ultimately, he hopes to see the systems streamlined and simplified to the point
where they can be used by patients at home. "We're not there yet, but we're
working on it!"
END
Digital Pulse Wave Analysis Offers Non-
Central Aortic Systolic Pressure (CASP) is one of the most powerful early predictors of cardiovascular risk. New digital pulse wave analysis technology is putting this valuable test in the hands of preventive primary care doctors.
Vol. 10, No. 2 Summer 2009