external counter pulsation therapy

7/28/2019 External Counter Pulsation Therapy

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EXTERNAL COUNTER PULSATION THERAPY

External Counter pulsation therapy is a non-invasive technique employing sequential inflation ofthree sets of lower extremity cuffs during diastole, with deflation at the onset of systole. Counter

pulsation Therapy increases venous return, augments diastolic pressure and provides pre systolic

unloading. Counter pulsation provides benefits of decreased anginal frequency, improvedexercise tolerance and improved stress myocardial perfusion in patients with chronic angina. It

has been postulated from its similarities to the IABP that the hemodynamic effects of Counter

pulsation result in collateral recruitment and/or development.

DESCRIPTION

EECP is a Noninvasive, a traumatic 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 aftercompletion of a course of therapy.

Enhanced External Counter pulsation 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 simultaneousdecompression 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 progressivelyincreased, as needed, to raise diastolic pressures gradually. Finger Plethysmography is used to

monitor correct timings.


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CONCEPT OF EXTERNAL COUNTER PULSATION

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 counter pulsation 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 referredto 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 bereduced. 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 besynchronized and phased with cardiac activity.

Studies of the hemodynamic effects of counter pulsation have revealed that several factors give

this modality the potential to assist patients with low cardiac output syndromes.


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Counter pulsation increases the stroke volume per unit work and; therefore, the efficiency

of the left ventricle. Either the left ventricular pressure or 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 counter pulsation

The evolution of counter pulsation techniques has been driven by the need to improve the

technical performance of equipment, and by the need to explore and demonstrate success inclinical applications.

Early research used direct counter pulsation techniques first developed by Harken and associatesat Harvard in the late 1950's. Through femoral cut down 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 counter

pulsation as a treatment following coronary occlusion. This finding provided the first evidence

that counter pulsation could quickly enhance the development of coronary collateral circulation,suggesting the possible clinical application of counter pulsation to the treatment of patients withcoronary 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 counter pulsation

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 counter pulsing actuator. There have been continuing developments in the design ofthe 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 coronarysurgery and in cariogenic shock. IABP offers advantages over direct counter pulsation in that itseffects are created close to the aorta, and the hemolysis associated with direct counter pulsation

is avoided.

In the mid 1960's, several scientists were involved in the evolution of counter pulsation to a

noninvasive technique using externally applied pressure generated by hydraulic systems. These


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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 counter pulsation devices were somewhat primitive, studies withthem 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 counter pulsation devices progressed, hydraulic systems

were replaced with pneumatics, and redesign of compression elements sought to improve resultsand 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 counter pulsation, Soroff and associates reported that mixedresults of clinical trials with these systems were owing to technical difficulties with the

equipment.

All of the external counter pulsation systems used in studies before the 1970's employed

"nonsequenced" pulsation - that is, compression of the vessels was performed simultaneouslyalong 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 outputand 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 andnonsequenced 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 Centerat 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 patientswith subacute pectoris refractory to other medical intervention and with evidence of myocardialischemia, were performed using a newly developed and "enhanced" counter pulsation system.

Designated EECP - Enhanced External Counter pulsation, the system employs a three-cuff

compression configuration and sophisticated computerized control of the inflation/deflationsequence. 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.


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THE STONY BROOK STUDIES

Cohn and Lawson and Lawon et al studied the efficacy and tolerability of EECP - Enhanced

External Counter pulsation in 18 patients with chronic, stable exertional angina pectoris. Allpatient 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 ofexercise achieved in the baseline study. The mean duration of exercise during maximal stress

testing increased by 1.58 minutes (p


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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 segmentdepression developed in the inferolateral leads, but was considered nondiagnostic because of the

abnormal baseline. No arrhythmia was noted during or after exercise. The perfusion scanindicated 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 luminaldiameter 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 2months, 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 therewas 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 oftreatment.

Fig. A. Baseline testing (after catheterization)


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Fig. B. Mid treatment with EECP (18 sessions)

Fig. C. Post treatment 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


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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 senseof 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 humansin 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 EECPoffers potential clinical benefits to patients who generally have little else

than medical therapy as a recourse. Studies have shown that treatment with EECP improvesangina 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 followingdisorders during the course of treatment with EECP:

Uncontrolled congestive heart failure

Severe valvular disease

Uncontrolled arrhythmia


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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 beatsper 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 bemeasured 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 mustadvise the treatment supervisorimmediately 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 anginalattack, 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 checkedthroughly 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 ofsuitable protective clothing, such as tights or bicycle pants worn during treatment.

external counter pulsation therapy

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