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EECP/ ENHANCED EXTERNAL COUNTERPULSATION
Noninvasive therapy for patients suffering with angina pectoris
Description
EECP is a Noninvasive, atraumatic procedure that can reduce the
symptoms of angina pectoris, presumably by increasing coronary
blood flow in ischemic areas of the heart.
The beneficial effects of EECP on perfusion of the ischemic myocardium
in patients with coronary artery disease appear to be sustained
between treatments, and may persist long after completion of a
course of therapy.
Enhanced External Counterpulsation involves the use of the EECP
Device to inflate and deflate a series of compressive cuffs wrapped
around the patient's calves, lower thighs, and upper thighs. Inflation
and deflation of the cuffs are modulated by events in the cardiac
cycle via computer-interpreted ECG signals.
During diastole, the cuffs inflate sequentially from the calves
proximally, resulting in augmented diastolic central aortic pressure
and increased coronary perfusion pressure. Compression of the
vascular bed of the legs also increases venous return and cardiac
output. Rapid and simultaneous decompression of the cuffs at the
onset of systole permits systolic unloading and decreased cardiac
workload. In the treatment regimen established to date, patients
are treated with EECP 1 hour daily for a total of 35 hours. At
that start of treatment, external compression is progressively
increased, as needed, to raise diastolic pressures gradually.
Finger plethysmography is used to monitor correct timings.
Concept of external counterpulsation
It has been more than 40 years since Kantrowitz and Kantrowitz
first described the principle of "phase shift diastolic augmentation"
(1953), and a group of physicians and physicists at Harvard and
elsewhere related this principle to the oxygen consumption difference
between flow work and pressure work by the heart. This understanding
led to the concept of mechanically-induced "counterpulsation"
to provide assistance to patients with low cardiac output syndromes.
The concept of counterpulsation is based on a favorable response
of the left ventricle to reduce arterial pressure during the systolic
period. Several investigators demonstrated good correlation between
oxygen consumption of the left ventricle (LVO2) and pressure time
(variously referred to as Tension Time Index [TTI] or pressure
time per minute [PTM]). These indices have been found to correlate
with maximal cardiac oxygen consumption under circumstances of
constant cardiac contractility and ventricular volume.
The heart can be rested, and its demand for oxygen reduced, if
left ventricular pressure can be reduced. However, effective perfusion
pressure must be maintained to meet the metabolic needs of the
body. Under the circumstance of decreased systolic pressure, diastolic
pressure must be increased in order to maintain effective perfusion.
This requires a system that can be synchronized and phased with
cardiac activity.
Studies of the hemodynamic effects of counterpulsation have revealed
that several factors give this modality the potential to assist
patients with low cardiac output syndromes.
- Counterpulsation increases the stroke volume per unit work
and; therefore, the efficiency of the left ventricle. Either
the left ventricular pressure and PTM (pressure time per minute)
are reduced, or the cardiac output is increased, or both.
- Diastolic perfusion pressure and the ratio of the mean diastolic
pressure to the mean systolic pressure are increased.
- Coronary flow increases preferentially with the diastolic
pressure since coronary vascular resistance is minimal during
cardiac diastole.
- The coronary collateral flow to ischemic regions of the myocardium
is increased.
- Modification of the pulse pressure distribution in the aorta
favors increased mean arterial pressure and; therefore, flow
to the vital organs.
Development and progress of counterpulsation
The evolution of counterpulsation techniques has been driven
by the need to improve the technical performance of equipment,
and by the need to explore and demonstrate success in clinical
applications.
Early research used direct counterpulsation techniques first
developed by Harken and associates at Harvard in the late 1950's.
Through femoral cutdown and external pulse actuation, this technique
withdrew and then returned the blood to the arterial system. In
a number of studies this direct technique was used to document
increased coronary flow, decreased coronary AVO2 difference, and
reduced left ventricular pressure work.
In the early 1960's laboratory studies with animals demonstrated
the potential efficacy of counterpulsation as a treatment following
coronary occlusion. This finding provided the first evidence that
counterpulsation could quickly enhance the development of coronary
collateral circulation, suggesting the possible clinical application
of counterpulsation to the treatment of patients with coronary
insufficiency and angina. While promising, it was also evident
that the requirement for femoral cutdown and hemolysis caused
by this technique severely limited the clinical usefulness of
this invasive approach.
Also at Harvard, during this same time period, Birtwell and Clauss,
produced counterpulsation by introducing a catheter with a long
slender balloon into the ascending aorta via the femoral artery
(Intra-aortic Balloon Pump [IABP]). Saline was pumped in and out
of this basoon by means of the cournterpulsing actuator. There
have been continuing developments in the design of the IABP and
its inflation/deflation techniques, and, although surgical insertion
is still required, this approach has found clinical application
in support of circulation during and after coronary surgery and
in cariogenic shock. IABP offers advantages over direct counterpulsation
in that its effects are created close to the aorta, and the hemolysis
associated with direct counterpulsation is avoided.
In the mid 1960's, several scientists were involved in the evolution
of counterpulsation to a noninvasive technique using externally
applied pressure generated by hydraulic systems. These systems
used various devices to encase the patient's lower limbs and compress
the vascular bed displacing arterial and venous blood centrally.
Although these early external counterpulsation devices were somewhat
primitive, studies with them demonstrated the potential of this
approach to increase survival in patients with myocardium infarction
and cariogenic shock, and in relief of angina pectoris.
As the evolution of noninvasive external counterpulsation devices
progressed, hydraulic systems were replaced with pneumatics, and
redesign of compression elements sought to improve results and
patient comfort. Clinical applications of this modality, beyond
cardiac or circulatory assistance in acute conditions, were also
explored with varying degrees of success. In a 1986 review of
the progress of external counterpulsation, Soroff and associates
reported that mixed results of clinical trials with these systems
were owing to technical difficulties with the equipment.
All of the external counterpulsation systems used in studies
before the 1970's employed "nonsequenced" pulsation
- that is, compression of the vessels was performed simultaneously
along the full length of the compression element.
During the late 1960', scientists at the National Institutes
of Health suggested that results could be improved if blood was
expressed from the extremities in a sequential manner. Development
and testing of these "sequenced" systems determined
that they achieved greater cardiac output and increased the ratio
of diastolic to systolic pressures than did nonsequenced systems.
During the 1970's, Zheng and colleagues at Sun Yat Sen University
in China, reported on their studies with a newly designed sequenced
pulsation system that used four sets of compression bladders on
the patient's legs, buttocks, and arms. In these trials, effects
of the sequenced system were studied in patients with angina pectoris
and acute myocardial infarction. In more than 90% of the 200 patients
with angina pectoris, this device provided long-term symptomatic
relief with minimal relapse.
These same investigators also compared the hemodynamic effects
of sequenced and nonsequenced compression, and various configurations
of compression devices in healthy volunteers and patients with
coronary heart disease. Results confirmed that sequenced systems
were far more effective in raising diastolic pressures.
Favorable results reported by Chinese investigators, led scientists
at the Health Sciences Center at the State University of New York
at Stony Brook, to reassess the efficacy of this modality in the
treatment of patients with chronic angina pectoris. Their studies,
which included patients with subacute pectoris refractory to other
medical intervention and with evidence of myocardial ischemia,
were performed using a newly developed and "enhanced"
counterpulsation system. Designated EECP - Enhanced External Counterpulsation,
the system employs a three-cuff compression configuration and
sophisticated computerized control of the inflation/deflation
sequence. It has been studied for its ability to provide both
short-term and sustained relief of symptoms of angina pectoris,
and to provide sustained improvements in perfusion of ischemic
areas of the myocardium.
THE STONY BROOK STUDIES
Cohn and Lawson and Lawon et al studied the efficacy and tolerability
of EECP - Enhanced External Counterpulsation in 18 patients with
chronic, stable exertional angina pectoris. All patient had incapacitating
symptoms, refractory to medical therapy, and exertional myocardial
ischemia documented by thallium-201 perfusion imaging. Eight patients
had previously undergone a total of 19 attempts at revascularization
by coronary bypass or angioplasty. Following an initial symptom-limited
stress thallium study, subjects received a total of 36 one-hour
treatments with EECP over a 7 week period. Antianginal medications
were continued at the initial or reduced doses. At the end of
the treatment period, thallium testing was repeated, followed
by routine maximal stress testing. I all patients, treatment with
EECP was associated with a substantial improvement in symptoms,
and 16 patients reported a complete absence on angina during their
usual activities. Repeat thallium testing showed a reduction in
myocardial ischemia in a significant proportion of patients: 12
(67%) demonstrated a complete absence of perfusion defects, and
2 (11%) demonstrated a reduction in the area of ischemia at the
level of exercise achieved in the baseline study. The mean duration
of exercise during maximal stress testing increased by 1.58 minutes
(p<0.005). In the subgroup of patients with improved thallium
scans, an increase in mean exercise duration of 1.86 minutes (p<0.001)
was observed; this was accompanied by a significant increase in
the double product (heart rate x systolic pressure at peak exercise).
There were no reported adverse effects of the treatments with
EECP.
Subsequent data from a group of 50 angina patients who were treated
with EECP are consistent with the above results. All of these
patients reported a reduction in symptoms, and 80% demonstrated
improvement by radionuclide testing. Patients with one- or two-vessel
disease were significantly more likely to respond than were those
with three-vessel disease.
Data from an initial follow-up study were available for 17 of
the original 18 patients studied, including 13 of the 14 patients
who had previously shown a reduction in myocardial ischemia. One
of these 13 patients suffered a myocardial infarction, and another
underwent a revascularization procedure during the intervening
period. Of the remaining 11 patients, all remained free of limiting
angina. Ten patients underwent stress thallium testing. In these
patients, the mean double product at 3 years was not significantly
different from the baseline value; however, eight patients (80%)
demonstrated persistent improvements in the results of thallium
scintigraphy.
A case history
A 64-year old accountant was sent by his cardiologist for an
exercise stress test and thallium perfusion scan on the basis
of reported chest pain. He was prescribed Tenormin, Cardizem,
and patch nitroglycerin.
Stress testing was performed using the Bruce protocol. The patient
exercised 5.5 minutes, but stopped because of progressive chest
discomfort. Workload reached was 7 METS. The resting heart rate
was 82/min and reached 118/min at peak exercise. Resting and peak
exercise blood pressure readings were 170/88 mm Hg and 150/88
mm Hg, respectively.
The resting electrocardiogram showed ST/T abnormalities. With
exercise, ST segment depression developed in the inferolateral
leads, but was considered nondiagnostic because of the abnormal
baseline. No arrhythmia was noted during or after exercise. The
perfusion scan indicated a large inferoapical defect with redistribution,
consistent with significant ischemia, but no other abnormalities
were seen.
The patient was referred for cardiac catheterization one month
later. Selective coronary arteriography revealed normal left main,
circumflex, and left anterior descending arteries. The proximal
right coronary artery also was normal, but there was a 95% reduction
in the luminal diameter of the mid-right coronary artery adjacent
to the origin of the second right ventricular branch. He had a
normal (65%) LVEF, but left ventricular end diastolic pressure
was severely elevated and moderate anterolateral hypokinesis was
observed in the ventriculogram. Angioplasty was recommended, but
the patient refused.
An offer was made to evaluate the patient for treatment with
EECP, and 7 months after the diagnostic catheterization, the patient
was reevaluated using stress/rest technetium-99m sestamibi with
SPECT imaging, under Bruce protocol. This procedure was repeated
2 months after 18 hours of EECP. Business concerns prevented continuation
of treatment for another 2 months, but thereafter, a further 18
hours of EECP were administered, followed by a post-treatment
stress/rest test with imaging.
Subjective improvements were noted by the patient after the first
18 hours of EECP and there was some indication of reduced
ischemia under stress. At the end of treatment there was further
subjective improvement and noticeable reduction in stress ischemia.
ST segment depression of 1.0 mm to 2.0 mm in the baseline peak
exercise ECG tracings resolved slightly by the end of treatment.
Fig. A. Baseline testing (after catheterization)
Fig. B. Midtreatment with EECP (18 sessions)
Fig. C. Posttreatment with EECP (36 sessions)
The following are pertinent inter-test comparative results.
OBSERVED CLINICAL EFFECTS
Based on observed response in clinical trials, therapy with EECP
can offer symptomatic and clinical relief in patients with angina
pectoris, including:
- Reduced need for antianginal medications
- Reduced frequency and intensity of chest pain
- Increased exercise tolerance
- Immediate and sustained improvement in myocardial perfusion
of ischemic areas
AS a result of symptomatic and clinical improvements, patients
have reported an improved sense of well-being and overall improvement
in quality of life.
Also, in a limited pilot study of psychosocial response to treatment
with EECP in the 18-patient initial Stony Brook study, investigators
noted that 67% of patients felt that their "family life had
improved" as a result of the treatment.
Why the effects of treatment with EECP may be
sustained
It is postulated that the repeated and pulsed increases in diastolic
pressure during therapy with EECP may enhance or stimulate the
opening of collateral channels in the coronary vascular system,
increasing perfusion of ischemic areas.
While the exact stimuli and mechanisms for the development of
coronary collaterals in humans in unknown, a report of an animal
study has shown that when diastolic pressures were raised above
systolic pressures, sequential external counterpulsation was effective
in increasing myocardial perfusion and promoted the formation
of collateral circulation.
Data from the follow-up studies at Stony Brook, demonstrate that
some of these patients have had initial and sustained (3-year)
improvement in myocardial perfusion of ischemic areas as demonstrated
through thallium-201 imaging, and suggest that these patients
may have responded to therapy with EECP through enhanced coronary
collateral development or function.
PATIENT SELECTION
EECP is a noninvasive external counterpulsation device
for the treatment of patients suffering from stable or unstable
angina pectoris.
Treatment with EECP offers potential clinical benefits
to patients who generally have little else than medical therapy
as a recourse. Studies have shown that treatment with EECP
improves angina symptoms and perfusion of ischemic regions
of the myocardium (assessed through scintigraphy) for up to 3
years following initial treatment.
Precautions
EECP should not be used for the treatment of patients
with, or who develop the following disorders during the course
of treatment with EECP:
- Uncontrolled congestive heart failure
- Severe valvular disease
- Uncontrolled arrhythmia
- Hemorrhage
- Coagulopathy
- Thrombophlebitis and peripheral vascular diseases involving
iliofemoral arterial obstruction
Patients with blood pressure higher than 180/110 mm Hg or a heart
rate of more than 120 beats per minute should have these conditions
brought under control before treatment commences.
PATIENT PREPARATION FOR TREATMENT
It is recommended that at each visit and before treatment begins,
the patient's resting blood pressure readings should be taken
and recorded. Sitting pulse and respiratory rates should also
be measured and recorded. The patient's legs should be examined
for areas of redness, ecchymosis, and/or signs of other vascular
problems.
For their comfort, and to prevent "chafing", patients
should be instructed to wear tight-fitting, seamless athletic
"tights" or bicycle pants made of stretchy, elastic
material during treatment.
Patients should be advised that is the pulsating sensation becomes
uncomfortable, they must advise the treatment supervisor immediately
so that treatment may be halted.
Patients should be advised to urinate immediately prior to treatment.
Treatment supervisors are advised to instruct patients about
the importance of keeping a daily "diary" of their angina
symptomology. Each patient should be instructed to record each
anginal attack, its time of occurrence, duration, severity, its
relationship to precipitating factors, and the number of nitroglycerin
tablets used to ease the attack. Patient diaries should be checked
throughly for accuracy and completeness at each visit for treatment.
ADVERSE EFFECTS
In studies to date, therapy with EECP has been well tolerated
by all patients enrolled. No patient withdrew after enrollment,
and there have been no reported complications.
Patients should not experience pain during treatment with EECP.
Discomfort from the pulsatile movement and pressure on legs and
buttocks may be eliminated or minimized through use of suitable
protective clothing, such as tights or bicycle pants worn during
treatment.
Contact Information
Gordon Fung M.D.
Program Director
Andrew Michaels, M.D.
Clinical Research Director
Dorothy Ruggles Stern RN
Program Coordinator
UCSF Medical Center at Mount Zion
1600 Divisadero Street, Rm. 222
San Francisco, Ca 94115-1609
Telephone: (415) 885 3636
Fax: (415) 885 3657
Email: EECP@ucsfmedctr.org
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