ECP is not a new invention. In fact, the basic theory and techniques of counterpulsation were developed more than 50 years ago by researchers at Harvard University and the Massachusetts General Hospital USA. These scientists sought to capitalize upon well-known hemodynamic and physiologic principles, by using them in the clinical setting to improve the care of patients with cardiovascular disease. Like any other muscle in the body, the heart depends upon a robust blood supply for the provision of oxygen and nutrients. As the coronary arteries and their tributaries penetrate and traverse the wall of the heart to deliver blood to the innermost portions of the muscle, the high pressures that are generated during systole are more than sufficient to impede, stop or even reverse the flow of blood through some of these vessels. Consequently, unlike the rest of the body, the heart receives approximately 80% of its blood supply during diastole, while it is at rest. The amount of oxygen that the heart uses to sustain its work is determined by the heart rate, contractility (a measure of the force of each contraction), and systolic wall tension (also referred to as “afterload”).

The amount of oxygen that is supplied to the myocardium is proportional to coronary blood flow, which is determined by diastolic blood pressure and coronary perfusion pressure. Based upon these facts, it follows that the ratio of myocardial oxygen supply to myocardial oxygen consumption is increased by lowering systolic blood pressure (systolic unloading) and/or by increasing diastolic blood pressure (diastolic augmentation). These physiologic principles are the basis for Counterpulsation (CP) Therapy.

The first attempts at CP utilized a femoral artery cannula, which was attached to an extracorporeal pump. The pump withdrew blood from the circulation during systole and returned it during diastole. This technique was shown to increase coronary artery blood flow and to reduce the workload and, subsequently, the oxygen consumption of the left ventricle. Unfortunately, the pumping mechanism resulted in an unacceptable amount of hemolysis, making this technique unsuitable for clinical use.

This work led to the development of an internal CP device known as the intra-aortic balloon pump (IABP). This device, basically a catheter with a balloon attached to its end, was inserted through the femoral artery and advanced to the descending aorta. By inflating the balloon during diastole, the IABP was shown to increase blood flow and oxygen to the heart through the coronary arteries. By deflating the balloon just before systole, both afterload and the heart’s overall workload were reduced. Not only did the IABP provide immediate relief to patients whose hearts were ischemic due to diseased coronary vessels, it also stimulated both the recruitment and the development of collateral vessels around the heart, providing new and permanent pathways for the delivery of blood and oxygen.

The mid-1960s saw the development the first external CP device. Taking advantage of the same physiology as the IABP, researchers designed a system that was extra-corporeal and completely noninvasive. This machine consisted of large, steel chambers that housed inflatable cuffs, which were part of a hydraulic circuit. The cuffs were wrapped around subject’s calves, thighs and buttocks and were inflated and deflated in synchrony with diastole and systole, respectively. As observed with intravascular or internal CP, external CP resulted in increased coronary blood flow and decreased left ventricular work and oxygen consumption. Unlike internal CP, however, external CP afforded the additional benefit of increased venous return (preload). In clinical application, external CP was shown to improve survival rates for patients with acute myocardial infarction, cardiogenic shock, and angina pectoris, but the results were not obtained consistently and the technique to did not gain much favor among clinicians. In addition, these initial results were significantly overshadowed by the even more impressive successes achieved through coronary artery bypass grafting and angioplasty, as these procedures were invented and refined in the 1970s. 

 Studies in China

Although interest in counterpulsation waned in the US, physicians in China remained very interested in the therapy. The medical establishment in China appreciated the cost-effectiveness of CP, and they felt that the principles of the therapy were congruent with the philosophy of Eastern medicine, which seeks treatments that aid and enhance the body’s innate ability to heal itself.

In the 1970s, Zheng and colleagues refined the technology behind external CP, ushering in the era of External Counter Pulsation or ECP. The hydraulic system that had been used to inflate and deflate the lower extremity cuffs in prior models was replaced with a pneumatic system, which made the system much less cumbersome. Their most important improvement to the procedure, however, was that their system was computerized and programmed to inflate the sets of cuffs sequentially, from the calves to the buttocks. This modification ensured that blood would flow retrograde, back toward the heart and the coronary vessels, during diastole.

 In the early 1980s, they reported on their extensive experience in treating angina with ECP. ECP reduced the frequency and severity of anginal symptoms during normal daily functions and exercise, furthermore, these benefits were sustained for years after therapy, in some cases.

By 1990, there were 1,800 ECP centers operating in China, and a study of more than 6,000 patients reported that this treatment had resulted in improvement for 90% of participants. Another study by Xu et al showed that 74% of ECP patients experienced improvement in symptoms of heart disease seven years after completing treatments and were four times less likely to suffer death from heart disease than patients treated with medication alone. This was extraordinary news for the medical world.

The United States Takes Notice

These results prompted a group of investigators (Lawson WE, Hui JCK, Soroff HS, et al) at the State University of New York at Stony Brook (SUNY) to undertake a number of open-label studies with the ECP system between 1989 and 1996 to see if they could reproduce the Chinese results, using both objective and subjective endpoints. Eighteen patients who suffered from debilitating angina, despite surgical intervention and medication, received 35 one-hour sessions of ECP over a period of 7 weeks. At the end of these treatments, all eighteen patients showed improvement in angina. Results showed that

	Sixteen patients (89%) could perform their normal daily activities without symptoms
	Twelve (66%) tested completely normal on nuclear stress tests following treatment, showing that normal blood flow had been reestablished in the heart, and
	Two (11%) had stress tests that, while still abnormal, were significantly improved.
	Stress test results were unchanged in four patients (22%).

A three-year follow up study by Lawson WE, Hui JCK, Zheng ZS, et al showed that eleven (79%) of participants still remained symptom free. The only treatments the subjects had received during that time had been adjustments to their medications and additional ECP treatments (8 patients).

By 1995 enough of a body of research had accumulated for ECP to received FDA approval as a treatment for chronic stable angina, cardiogenic shock, and for use during a heart attack. Most recently, in June of 2002, the FDA approved the use of ECP for congestive heart failure.

 The MUST-EECP Trial

For many years critics claimed that no double-blind studies existed to prove the effectiveness of ECP, but this changed in 1995 when Vasomedical Inc., USA began a large, randomized, controlled, doubleblinded clinical trial called the “Multicenter Study of Enhanced External Counterpulsation (MUST- EECP).

Cardiologists at seven leading university hospitals, including Columbia, Yale, and Harvard, conducted research on 139 participants. Half of these patients received thirty-five real ECP treatments and the other half received thirty-five placebo treatments (cuffs squeezing only minimally while the patient lay on the treatment bed).

Patients received treadmill stress tests both before and after receiving each ECP treatment. Following treatments, the participants in the group who had received ECP were able to exercise significantly longer without symptoms or change to their EKG, had less angina symptoms, and used less nitroglycerin. This proved that they had more blood and oxygen circulating through their hearts. Both at the completion of the thirty-five-hour course of treatments and when patients were retested one year later, those who had actually received ECP continued to show sustained improvement in their ability to work and perform daily activities. They also reported less pain, more energy, greater ability to socialize, less anxiety and depression, and lower levels of angina (Arora et al).

The results of the MUST-EECP study were presented at the annual Scientific Sessions of the American Heart Association in November of 1997 and the American College of Cardiology in March of 1998. The Journal of the American College of Cardiology, a major peer-reviewed medical journal, published the results of the MUST-EECP trial in June 1999.