2005

Enhanced External Counterpulsation: An Effective Noninvasive Outpatient Treatment for Select Refractory Angina Patients

Points to Remember

• As the population ages and medical care improves, the number of patients who survive coronary events and experience refractory angina will increase.
• This patient group needs alternatives to standard revascularization procedures.
• Enhanced external counterpulsation (EECP) is the only truly noninvasive outpatient therapy alternative clinically available for refractory angina.
• Data from small trials and a large international registry indicate EECP provides both short-term and long-term relief of anginal symptoms and improved quality of life for many patients with symptomatic ischemic heart disease.
• Mayo Clinic's EECP lab is a leading center in the clinical application and research investigation of this technology.

Scope of Problem

Approximately 6.4 million US patients have symptomatic coronary artery disease (CAD). Another 400,000 new cases occur each year. The total number of CAD patients is likely to increase with the documented increase in obesity and as the population ages. In addition, as survival after primary coronary events improves, the incidence of patients with unrevascularizable CAD and medically refractory angina also continues to increase, and alternative therapies are urgently needed.

Standard Treatments and Their Limitations

Medically refractory angina is generally treated by revascularization procedures such as coronary artery bypass graft surgery or percutaneous coronary intervention. Yet for a considerable segment of this population, standard revascularization procedures are not appropriate because of previous revascularization attempts, unsuitable coronary anatomy, or other comorbid conditions. Although alternatives exist, such as neurostimulation and laser revascularization techniques, they are invasive and may be contraindicated in certain patient conditions.

A New Approach: EECP

Enhanced external counterpulsation (EECP) is an effective, noninvasive symptom-control strategy with an excellent safety profile. EECP both reduces angina symptoms and improves objective measures of myocardial ischemia. It is approved by the US Food and Drug Administration for the treatment of patients with angina and accompanying cardiac diseases.

EECP uses a series of pneumatic cuffs on each leg to apply sequential pressure pulses that increase blood flow. By so doing, the cuffs essentially exercise the patient's circulatory system. A standard EECP course consists of 35 EECP treatments of 1 hour each over a 7-week period.

During each session, the patient's legs are wrapped in 3 pairs of pneumatic cuffs around the calves, around the lower thighs, and around the upper thighs. Compressed air is used to inflate the cuffs sequentially, from distal to proximal, in early diastole. The cuffs are then rapidly deflated at the onset of systole. The sequential cuff inflation raises the diastolic pressure while the rapid cuff deflation promotes "arterial runoff" to the lower extremities.

This effect is similar to intra-aortic balloon counterpulsation (IBC). However, unlike IBC, EECP also enhances venous return, which increases cardiac output.

EECP Benefits

Because of its noninvasive and outpatient nature, EECP offers substantial savings in terms of financial, physical, and psychosocial costs compared with invasive and minimally invasive revascularization procedures. Several small trials demonstrate a consistently positive clinical response to EECP. Among these desirable effects are:

• Reduction of angina
• Reduction in nitrate use
• Increased exercise tolerance
• Enhanced quality of life and favorable psychosocial effects
• Prolongation of the time to exercise-induced ST-segment depression
• Enhanced coronary perfusion
• Increase in organ blood flow
• Improvement in endothelial function Follow-up data suggest that clinical benefits may last for up to 5 years in patients who show an initial favorable response.

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EECP Disadvantages

Despite the obvious advantages of EECP, its use has some limitations:

• Limited availability in the United States
• Commitment of 35 hours for treatment over a 7-week period
• Mechanism is not well understood. Possible explanations include:
  1. hemodynamic effects of EECP that lead to increased blood flow in multiple vascular beds, including coronary arterial circulation;
  2. enhancement of vascular sheer stress, which in turn favorably affects endothelial function and collateral development;
  3. reduction of oxidative stress, which is associated with various cardiovascular risk factors and is considered a key factor in developing atherosclerosis and endothelial dysfunction.

Indications for Use

EECP provides symptomatic benefit in a broad range of clinical states. It is particularly useful in patients with severe, limiting symptoms of ischemic coronary disease despite an optimal medical regimen and for whom standard revascularization is not an option. Safety and efficacy in other disease states, including vasospastic angina, endothelial dysfunction, and heart failure, are under investigation.

Contraindications for Use

Standard contraindications to EECP include active deep venous thrombosis, clinically significant aortic regurgitation, and severe, uncontrolled hypertension.