Abstract
The aim was to explore the effectiveness of enhanced external counterpulsation (EECP) therapy in patients with severe angina pectoris/ chronic heart failure symptoms, who were not suitable candidates for invasive treatment. This retrospective study employed a comprehensive methodology that includes individualized treatment, continuous monitoring, and thorough pre- and postprogram evaluations to assess the efficacy of EECP therapy. The standard protocol involved 35 one-hour treatments, with flexibility for extensions based on therapeutic progress. When pre- and posttreatment results were analyzed, EECP improved the original functional class compared with pretreatment. The mean difference in the functional class was 1.32 (0.92), p < 0.0001. Six-minute walk (6MW) distance improved from 383.6 m (110.24) to 423.1 m (121.50) with mean difference of 37.1 (44.99), p < 0.0001. Duke Activity Status Index (DASI) score improved from 3.9 (2.75) to 6.0 (4.17) with mean difference of 2.16 (3.8), p < 0.0001. Training metabolic equivalents (METs) improved from 3.0 (0.74) to 4.0 (1.57) with mean difference of 1.04 (1.2), p < 0.0001. Weekly anginal events decreased from 13.1 (13.19) to 3.2 (7.38) with mean difference of –9.78 (11.7), p < 0.0001. EECP resulted in improvement of angina pectoris functional class, the 6MW distance, reduction in the number of hospitalizations in first year posttreatment, a significant decrease in sublingual nitroglycerin use, improvement of systolic and diastolic blood pressure, and improvement of DASI score.
Keywords: angina pectoris, congestive heart failure, coronary artery disease, external counterpulsation therapy, myocardial ischemia
Ischemic heart disease is associated with an inadequate supply of blood to the myocardium. 1 This disease process is secondary to the obstruction of the epicardial coronary arteries, usually from atherosclerosis. Patients may have chronic (stable) or acute (unstable) disease. 2
Most patients are diagnosed early and treated with medications and revascularization therapy. However, some patients are resistant to these treatments and develop refractory angina. Refractory angina is caused by the inadequate response of chest pain to antianginal agents or in cases when the coronary vasculature is not amenable to revascularizations (percutaneous coronary interventions [PCIs] or coronary artery bypass surgery [CABG]). Many of these patients continue to experience residual anginal symptoms despite maximal medical therapy. Furthermore, certain patients are not suitable candidates to undergo cardiac procedures or revascularization due to multiple comorbidities, such as renal disease, severe pulmonary disease, or overall poor health.
Enhanced external counterpulsation (EECP) therapy is a nonpharmacologic, noninvasive outpatient treatment approved by the United States Food and Drug Administration since 1995. The American College of Cardiology/American Heart Association guidelines recommend the use of EECP in patients with chronic stable angina pectoris who remain symptomatic despite optimal medical therapy and those who are not candidates for coronary revascularization. EECP holds a class IIb recommendation according to present guidelines. 3 4 5 6 7 8 EECP therapy has been recommended more commonly for patients with chronic angina due to ischemic heart disease but also for patients with symptomatic heart failure. 6 7 8 Several studies have demonstrated that EECP reduces anginal events per Canadian Cardiovascular Society (CCS) angina classification, improves hemodynamics, increases exercise capacity, improves quality of life, increases time to exercise to induce ST segment depression, and improves myocardial perfusion. 9 10 11 12 13 14 15 16
Despite the improvements in treatment options for coronary artery disease (CAD), the data from various observational studies have provided limited evidence to prove the effectiveness of the EECP. This study aims to provide more data regarding EECP treatment in patients with refractory angina pectoris and heart failure at one of the Mayo Clinic facilities in Southwest Wisconsin.
Methods
Participant Characteristics
The study enrolled 93 patients of which 77 patients completed EECP therapy. Patients were screened prior to enrollment using specific inclusion and exclusion criteria. Inclusion criteria included patients aged 21 to 94 years, symptoms consistent with CCS Classification angina levels I IV, documented evidence of CAD or congestive heart failure (CHF), and symptoms consistent with class III and IV as an indication for EECP. Exclusion criteria involved contraindications such as bleeding diathesis, active thrombophlebitis, severe lower extremity vaso-occlusive disease, aortic aneurysm requiring surgical repair, specific arrhythmias, severe aortic or mitral valve issues, and pregnancy. Relative contraindications included conditions like decompensated CHF, uncontrolled blood pressure (BP), history of varicosities, deep vein thrombosis, and warfarin use with an international normalized ratio exceeding 3.5.
Procedure
The study employed EECP therapy, utilizing equipment trademarked by Vasomedical Inc., consisting of three pairs of pneumatic cuffs applied strategically around the calves, thighs, and buttocks. The cuffs were inflated sequentially upward at the onset of diastole and released rapidly before the onset of systole, producing retrograde blood flow or “aortic counter pulsation” in the aorta ( Fig. 1 ). This resulted in diastolic blood flow augmentation, increased venous return, and improved coronary perfusion pressure during diastole. 17 The pressure utilized ranged from 240 to 300 mm Hg, and continuous monitoring of heart rate, rhythm, and pulse oximetry was maintained throughout a 60-minute treatment. Finger plethysmography demonstrating augmentation of diastolic pressure with cuff inflation is shown in Fig. 2 .
Fig. 1.
Mechanism of enhanced external counterpulsation (EECP) showing sequential cuff inflation and deflation.
Fig. 2.
Finger plethysmograms. Comparison of no enhanced external counterpulsation (EECP) versus EECP.
Patients underwent a standard protocol of 35 one-hour EECP treatments, with the option for extensions based on late therapeutic improvements. Posttreatment, the patient's BP was reevaluated, and potential skin irritation on the legs was examined before discharging the patient.
Evaluation of Patients
Patients were assessed in the pre- and postprogram format. The 6-minute walk (6MW) test was completed on all patients unless contraindicated due to fall risk or cognitive impairment. Data points collected from the 6MW test included pre- and postwalk heart rates, oxygen saturation, and BP. Symptoms induced during the 6MW were also measured. The 6MW test was utilized to capture the symptoms of potentially undiagnosed peripheral vascular disease.
Clinical data was reviewed to collect angina pectoris history or heart failure classification. Patients with a primary diagnosis of ischemic coronary heart disease were classified according to the CCS Grading System. Alternatively, patients with a primary diagnosis of CHF were classified per the New York Heart Association Functional Classification. Clinical information was also used to collect data regarding hospitalizations and cardiac rehabilitation training levels (in metabolic equivalents [METs]).
Informed consent is not required as part of the study design. The study was performed per Mayo Clinic's Ethics Committee guidelines.
Statistical Analyses
The descriptive characteristics of the patients who participated in the study are summarized as number (%) for categorical variables and mean (± standard deviation [SD]) for continuous variables. The differences between the pre- and post-EECP outcomes of angina pectoris and CHF variables were compared using the Wilcoxon signed rank test. A two-sided p -value of < 0.05 was considered statistically significant. All analyses were performed independently by the authors using SAS 9.4 (SAS Institute, Cary, NC) and R version 4.1.2 (R Foundation, Vienna, Austria).
Results
We recruited 93 patients between 2009 and 2021 in our EECP laboratory. Only 77 patients completed the therapy and were included in the study. However, 16 patients could not complete the procedure for various reasons such as CHF exacerbation, worsening chest pains, neuropathy pain, exacerbation of chronic obstructive pulmonary disease, and skin breakdown. Two patients died during the therapy period for reasons not related to EECP.
The mean age of the patients was 68.1 (11.00) years. There were 70 males (75.3%) and 23 females (24.7%). Due to extensive and severe CAD, prior revascularization, left ventricular (LV) dysfunction, comorbid conditions, and high-risk profile, none of the patients were candidates for any further revascularization. Sixty-five percent of patients had a primary diagnosis of CAD, and 15% of the patients had a primary history of CHF. All patients were symptomatic in terms of angina or anginal equivalent. There was a high prevalence of cardiac risk factors, including hypertension (77%), diabetes mellitus (40%), and dyslipidemia (78%).
Antiplatelet, beta-blockers, calcium-channel blockers, angiotensin-converting enzyme inhibitors, angiotensin receptor blockers, lipid-lowering drugs, and diuretics were similar at baseline and 2 years' follow-up.
Post-EECP therapy, improvement in the functional class, 6MW distance difference, pre- and post-Duke Activity Status Index (DASI) score, training METs, weekly angina events, heart failure (HF) symptoms, nitroglycerin (NTG) use per week, and systolic (SBP) and diastolic BP (DBP) were improved. The mean number of hospitalizations decreased from 1.3 (1.28) to 0.6 (0.79). See Fig. 3 .
Fig. 3.
Statistical analyses of data in pre- and post-enhanced external counterpulsation (EECP) groups in patients with coronary artery disease (CAD) (mean and standard deviation [SD]).
The treatment of EECP improved the functional class of angina pectoris in comparison to the classification before the treatment. The mean difference in the functional class was: 1.32 (0.92 SD), p < 0.0001. 6MW distance improved from 383.6 m (110.24 SD) to 423.1 m (121.50 SD) with mean difference of 37.1 m (44.99 SD), p < 0.0001. DASI score improved from 3.9 (2.75 SD) to 6.0 (4.17 SD) with mean difference of 2.16 (3.8 SD), p < 0.0001. Training METs improved from 3.0 (0.74 SD) to 4.0 (1.57 SD) with mean difference of 1.04 (1.2 SD), p < 0.0001. Weekly anginal events decreased from 13.1 (13.19 SD) to 3.2 (7.38 SD) with mean difference of –9.78 (11.7 SD), p < 0.0001. HF symptoms improved from 30.0 (36.17 SD) to 7.8 (9.55 SD) with mean difference of –25.3 (36.35 SD). The weekly NTG usage was decreased after treatment, mean decreased from 1.8 (4.13 SD) to 0.4 (1.09 SD) with a difference of –1.36 (4.0 SD), p < 0.0006. Average SBP decreased from 121.0 (11.85 SD) to 117.1 (13.94 SD) with difference of –3.97 (12.8 SD), p < 0.01. Average DBP decreased from 69.0 (9.83 SD) to 67.0 (6.70 SD) with mean difference of – 2.17 (9.2 SD), p = 0.046. Health-related quality of life improved from 40.6 (10.25 SD) to 45.4 (9.22 SD) with mean difference of 5.34 (7.8 SD), p = 0.003. Posttreatment 1 year hospitalization rates decreased from 1.3 (1.28 SD) to 0.6 (0.79 SD), difference of –0.65 (1.3 SD), p = 0.005. See Table 1 and Figs. 4 5 6 .
Table 1. Pre- and post-EECP results in CAD patients ( p -values) with angina pectoris .
| Variable | Mean (SD) | Median | IQR | p -Value a |
|---|---|---|---|---|
| Difference 6-minute walk | 37.13 (45) | 33.55 | 50.1 | < 0.0001 |
| Difference functional class | –1.32 (0.92) | –1.00 | 1.0 | < 0.0001 |
| Difference DASI score | 2.16 (3.8) | 1.25 | 3.8 | < 0.0001 |
| Difference training METs | 1.04 (1.2) | 0.90 | 1.2 | < 0.0001 |
| Difference weekly anginal events | –9.78 (11.7) | –4.00 | 15.0 | < 0.0001 |
| Difference NTG per week | –1.36 (4.0) | 0.0 | 1.0 | 0.0006 |
| Difference systolic BP | –3.97 (12.8) | –3.0 | 18.0 | 0.01 |
| Difference diastolic BP | –2.17 (9.2) | –2.17 | 6.0 | 0.046 |
| Difference HRQOL | 5.34 (7.8) | 4.0 | 12.0 | 0.003 |
| Difference hospitalizations | –0.65 (1.3) | –1.0 | 1.0 | 0.005 |
Abbreviations: BP, blood pressure; CAD, coronary artery disease; DASI, Duke Activity Status Index; EECP, enhanced external counterpulsation; HRQOL, health-related quality of life; IQR, interquartile range; MET, metabolic equivalent; NTG, nitroglycerin; SD, standard deviation.
Application of Wilcoxon signed ranked test.
Fig. 4.
Pie chart showing groups of patients with coronary artery disease (CAD) in New York Heart Association (NYHA)/Canadian Cardiovascular Society (CCS), functional class 1–4, pre- and post-enhanced external counterpulsation (EECP). Note that post-EECP treatment, all functional classes improved.
Fig. 5.
Nitroglycerin use decreased after enhanced external counterpulsation (EECP) treatment in coronary artery disease (CAD) patients.
Fig. 6.
DASI (Duke Activity Status Index) pre- and post-enhanced external counterpulsation (EECP) therapy in coronary artery disease (CAD) patients. DASI score improved significantly after EECP treatment.
Discussion
This retrospective study with a 1-group pretest-posttest design examined the pre- and post-EECP follow-up effects in patients with severe refractory angina or anginal equivalents, who remained symptomatic following conventional medical treatments including but not limited to PCI, CABG, and maximal medical management. A total of 93 patients (23 females, 70 males, 38–93 years of age) with chronic stable refractory angina pectoris or anginal equivalent who were consecutively treated with EECP at the Mayo Clinic Health System, La Crosse, WI, were included in this study. All the patients were referred for EECP by their cardiologists if they had exhausted options for optimal medical management or could not undergo additional coronary interventions for various reasons. Some of the patients who refused traditional therapies were also referred for EECP. American College of Sports Medicine-certified clinical exercise physiologists administered the treatment under the supervision of a board-certified cardiologist. The usual side effects were equipment-related, including leg pain, back pain, skin abrasions, blistering, claustrophobia, and paresthesia. The criteria for chronic stable refractory angina were defined as “a chronic condition characterized by the presence of chronic angina (more than 3 months' duration) caused by coronary insufficiency in the presence of CAD which cannot be controlled by a combination of medical therapy, angioplasty, and coronary bypass surgery.” 2 More specifically, as stated by the Centers for Medicare and Medicaid Services in the National Coverage Database: As of July 1, 1999, coverage is provided for the use of EECP for patients who have been diagnosed with disabling angina (class III or class IV, CCS Classification or equivalent classification) who, in the opinion of a cardiologist or cardiothoracic surgeon, are not readily amenable to surgical intervention, such as percutaneous transluminal coronary angioplasty or cardiac bypass, because: (1) Their condition is inoperable, or patients were at high risk of surgical complications or postoperative failure; (2) Their coronary anatomy was not readily amenable to such procedures; or (3) They had comorbid states, which posed an excessive risk. 17
As a result of this treatment, most patients experience increased time until the onset of ischemia, increased exercise tolerance, and a reduction in the number and severity of anginal episodes. Evidence was presented that this effect lasted well beyond the immediate posttreatment phase, with patients becoming symptom-free for several months to 2 years.
Many patients with refractory angina are so severely symptomatic and physically limited that they cannot exercise to the degree where cardiovascular benefits are elicited. 18 The limitations that patients experience are classified based on symptoms (chest pain, dyspnea, and palpitations) concerning their physical activity. The patient's functional limitation is graded according to the CCS Classification (CCS score class I to IV), where a higher class indicates more significant physical limitation. Presence of anginal symptoms in daily life is also strongly associated with mental stress. 19 Cardiac anxiety, a subtype of anxiety, is related to perceived cardiac sensations and the patient's feelings of hypersensitivity in these regards. This sometimes chronic, heightened anxiety can lead to a more negative quality of life for the patient. 20 21 22 The primary goal of therapy for these patients is to improve anginal symptoms, thereby relieving the associated physical and psychological stress, resulting in improved quality of life. 23
Our results corroborate some previous results indicating that EECP therapy significantly reduces the angina class in patients with chronic angina pectoris. 11 In addition, there was a significant improvement in the 6MW distance, DASI score, training METs, weekly anginal events, and frequency of hospitalizations at 1- and 2-year follow-up. The mechanisms leading to the clinical benefit of EECP are incompletely understood. However, it is known that EECP increases the venous return, increases the diastolic aortic pressure, reduces the systolic pressure, and overall improvement in the cardiac output, like intra-aortic balloon pump mechanics proposed as a primary reason for clinical improvement. 17 The current evidence suggests that EECP also improves endothelial function by increasing the blood flow in multiple vascular beds, including the coronary circulation, resulting in endothelial shear stress, thereby stimulating the release of vasodilators like nitric oxide, thereby reducing the release of vasoconstrictors like endothelin-1. Shear stress is known to be a significant stimulus for collateral blood vessel development and recruitment. It is already established that EECP therapy has been associated with the release of angiogenic factors such as vascular endothelial growth factors, fibroblast growth factors, and hepatocyte growth factors. This evidence suggests that EECP benefits by enhancing coronary collateral vascularization. 17
The CCS functional class improvement noted in this study was seen across the board from class II through IV. Posttreatment, we noted more patients in class I (from 3.8 to 39%) due to improvement from a higher class. The M-EECP trial, the first randomized control study to evaluate EECP, reported that EECP can reduce angina and extend the time to ischemia in patients with symptomatic CAD. 10
The results of our study also show that EECP treatment improved the BP in patients with refractory angina. It was noted that EECP treatment decreases SBP and DBP compared with patients receiving optimal medical treatment only. It was also noted that BP response did correlate with a reduction in anginal frequency.
Soran et al published data from the International EECP Patient Registry and summarized 2-year clinical outcomes after EECP therapy in patients with refractory angina and LV dysfunction. 24 The study included a sample of 363 subjects. Of those, 77% demonstrated an improvement of at least anginal class, with 18% of those patients having no angina following a course of EECP. Additionally, 52% of the subjects had discontinued their NTG usage. At 2-year follow-up, 83% of the subjects had survived, with 43% of those having no hospitalizations. Of the patients who reported improvement of anginal symptoms after therapy, 55% of those reported maintenance of those improvements.
It is essential that additional prospective studies be done to corroborate these positive outcomes. It would be helpful to conduct studies with follow-up periods of more than 1 year to obtain more reliable performance measures regarding the therapeutic role and long-term benefits of EECP. The limitation of our study is that there is no control group of patients with refractory angina receiving subtherapeutic level EECP (or no EECP treatment) for comparison. Multicenter studies would be particularly advantageous in proving the significance of findings. However, such studies would be complex due to the need for uniformity of outcomes collection.
Conclusion
This review shows that in patients with angina pectoris/CHF, EECP shows symptomatic improvement. For patients with severe angina who are intolerant or not responding adequately to optimum treatment, EECP resulted in improvement of angina pectoris functional class, the 6MW distance, reduction in the number of hospitalizations in first year posttreatment, a significant decrease in sublingual NTG use, improvement of SBP and DBP, and improvement of DASI score. Although our results show the safety and efficacy of EECP in patients with chronic severe angina pectoris despite optimal medical therapy, there is a need for more controlled studies to validate the results in larger trials.
Acknowledgment
We acknowledge the expert statistical help and analysis of the data by Ramy Mehta, Principal Statistician, Mayo Clinic, Rochester, MN 55905.
Funding Statement
Funding None.
Conflict of Interest None declared.
Note
All authors had access to the data and a role in writing this manuscript. The concept and design of the study was planned and completed by T.T.
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