Maximizing the hemodynamic benefit of enhanced external counterpulsation

A patient-specific modelling method of blood circulatory system for the numerical simulation of enhanced external counterpulsation

Lumped parameter model (LPM) is a common numerical model for hemodynamic simulation of human's blood circulatory system. The numerical simulation of enhanced external counterpulsation (EECP) is a typical biomechanical simulation process based on the LPM of blood circulatory system. In order to simulate patient-specific hemodynamic effects of EECP and develop best treatment strategy for each individual, this study developed an optimization algorithm to individualize LPM elements. Physiological data from 30 volunteers including approximate aortic pressure, cardiac output, ankle pressure and carotid artery flow were clinically collected as optimization objectives. A closed-loop LPM was established for the simulation of blood circulatory system. Aiming at clinical data, a sensitivity analysis for each element was conducted to identify the significant ones. We improved the traditional simulated annealing algorithm to iteratively optimize the sensitive elements. To verify the accuracy of the patient-specific model, 30 samples of simulated data were compared with clinical measurements. In addition, an EECP experiment was conducted on a volunteer to verify the applicability of the optimized model for the simulation of EECP. For these 30 samples, the optimization results show a slight difference between clinical data and simulated data. The average relative root mean square error is lower than 5%. For the subject of EECP experiment, the relative error of hemodynamic responses during EECP is lower than 10%. This slight error demonstrated a good state of optimization. The optimized modeling algorithm can effectively individualize the LPM for blood circulatory system, which is significant to the numerical simulation of patient-specific hemodynamics.

Impact of Enhanced External Counterpulsation on Peripheral Circulation

Enhanced external counterpulsation (EECP) is a noninvasive counterpulsation technique that reduces angina and improves exercise capacity in patients with coronary artery disease. Diastolic coronary perfusion is augmented by pneumatic compression of 3 sets of cuffs wrapped around the lower extremities. Although central hemodynamic changes are well investigated, almost no data exist about the changes of peripheral circulation during EECP. In this study, 12 patients with angina and angiographic evidence of coronary artery disease were treated for 1 hour with EECP. In these patients, peripheral artery disease was excluded by duplex sonography. The patients rested 1 hour before EECP in supine position, and they remained in that position for 1 hour after the procedure. Changes of flow volumes and flow pattern of the posterior tibial artery and the brachial artery were measured by sonography at the end of all 3 periods. Furthermore, we measured the concentration of circulating prostanoids at these 3 time points. Averaged flow volume of the posterior tibial artery decreased to 69% ± 23% (P < .05) during EECP and increased to 133% ± 34% (P < .05) of baseline 1 hour after the procedure. In contrast, the averaged flow volume of the brachial artery increased by 9% ± 4% (P < .05) during EECP and returned to baseline values after EECP. The flow pattern of the posterior tibial artery showed a second early diastolic antegrade flow caused by the cuff inflation and a reverse end-diastolic flow after the deflation of the cuffs. These flow changes caused an increase of the pulsatility index by Gosling (397% during EECP), returning to baseline values in the recovery period. Plasma concentrations of circulating prostanoids showed no significant change during EECP. Thus, pedal flow volume decreased to approximately two thirds of baseline during EECP followed by reactive hyperemia even 1 hour after the procedure; however, this decreased perfusion triggered no change of the prostacyclin/thromboxane ratio and was well tolerated by all investigated patients. The observed 4-fold increase of the peripheral pulsatility index supports the thesis of increase of shear-stress—related improvement of endothelial function during EECP.

Enhanced external counterpulsation improves endothelial function and exercise capacity in patients with ischaemic left ventricular dysfunction

Enhanced external counterpulsation (EECP) therapy decreases angina episodes and improves quality of life in patients with left ventricular (LV) dysfunction (LVD). However, studies have not elucidated the mechanisms of action and overall effects of EECP in patients with LVD. The purpose of the present study was to investigate the effects of EECP on endothelial function in peripheral conduit arteries and exercise capacity (peak Vo2 ) in patients with LVD. Patients with ischaemic LVD (ejection fraction (EF) 34.5 ± 4.2%; n = 9) and patients with symptomatic coronary artery disease (CAD) and preserved LV function (EF 53.5 ± 6.6%; n = 15) were studied before and after 35 sessions (1 h) of EECP. Brachial and femoral artery flow-mediated dilation (bFMD and fFMD, respectively) were evaluated using high-resolution ultrasound. Enhanced external counterpulsation elicited similar significant improvements in the following FMD parameters in the CAD and LVD groups (P ≥ 0.05 between groups for all): absolute bFMD (+53% and +70%, respectively), relative bFMD (+50% and +74%, respectively), bFMD normalized for shear rate (+70% and +61%, respectively), absolute fFMD (+33% and +21%, respectively) and relative fFMD (+32% and +17%, respectively). In addition, EECP significantly improved plasma levels of nitrate/nitrite (+55% and +28%) and prostacyclin (+50% and +70%), as well as peak Vo2 (+36% and +21%), similarly in both the CAD and LVD groups (P ≥ 0.05 between groups for all). Despite reduced LV function, EECP therapy significantly improves peripheral vascular function and functional capacity in CAD patients with ischaemic LVD to a similar degree to that seen in CAD patients with preserved LV function.

Increasing pressure of external counterpulsation augments blood pressure but not cerebral blood flow velocity in ischemic stroke

External counterpulsation (ECP) is a noninvasive method used to augment cerebral perfusion but the optimal use of ECP in ischemic stroke has not been well documented. We aimed to investigate the effects of ECP treatment pressure on cerebral blood flow and blood pressure (BP). We recruited 38 ischemic stroke patients with large artery occlusive disease and 20 elderly controls. We commenced ECP treatment pressure at 150 mmHg and gradually increased to 187.5, 225 and 262.5 mmHg. Mean cerebral blood flow velocities (CBFV) of bilateral middle cerebral arteries and continuous beat-to-beat BP were recorded before ECP and during each pressure increment for 3 minutes. Patient CBFV data was analyzed based on whether it was ipsilateral or contralateral to the infarct. Mean BP significantly increased from baseline in both stroke and control groups after ECP commenced. BP increased in both groups following raised ECP pressure and reached maximum at 262.5 mmHg (patients 16.9% increase versus controls 16.52%). The ipsilateral CBFV of patients increased 5.15%, 4.35%, 4.55% and 3.52% from baseline under the four pressures, respectively. All were significantly higher than baseline but did not differ among different ECP pressures; contralateral CBFV changed likewise. Control CBFV did not increase under variable pressures of ECP. ECP did increase CBFV of our patients to a roughly equal degree regardless of ECP pressure. Among the four ECP pressures tested, we recommend 150 mmHg as the optimal treatment pressure for ischemic stroke due to higher risks of hypertension-related complications with higher pressures.

The safety and efficacy of enhanced external counterpulsation as a treatment for angina in patients with aortic stenosis

BACKGROUND

Comorbid aortic stenosis (AS) has been considered a precaution when applying enhanced external counterpulsation (EECP) to individuals with angina due to concerns about treatment-related hemodynamic changes.

HYPOTHESIS

The aim of this study was to determine whether EECP safely reduces symptoms of myocardial ischemia and improves hemodynamics in individuals with AS.

METHODS

Forty-three patients with AS (average age, 73 years; 86% male) and 43 comparison patients without AS were chosen from a database of 1327 EECP patients. Canadian Cardiovascular Society (CCS) Functional Angina Classification, diastolic augmentation ratio, and blood pressure were measured at baseline and on completion of the course of EECP.

RESULTS

Thirty-five of the 43 patients with AS (81%, 95% CI: 66.6% to 91.6%) and 38 of the 43 without AS (88%, 95% CI: 74.9% to 96.1%) improved in angina class (P < 0.0001). There was no statistical difference between the percentages in patients with and without AS (P = 0.54). CCS angina class outcome was not associated with AS severity (P = 0.55). The percentage of patients with diastolic augmentation ratio ≥1.0 was 16.3% in both groups at baseline and improved to 39.5% in AS patients and 37.2% in non-AS patients after EECP (both P = 0.002). The average decreases in systolic blood pressure in subjects with AS (-15 mm Hg, 95% CI: 11 to 20, P < 0.0001) and without AS (-18 mm Hg, 95% CI: 14 to 22, P < 0.0001) were similar (P = 0.31). No major adverse cardiac events were reported.

CONCLUSIONS

Angina patients with AS who undergo EECP had clinically important symptomatic and hemodynamic improvements comparable to their non-AS counterparts.

Vasculoprotective properties of enhanced external counterpulsation for coronary artery disease: beyond the hemodynamics

A growing pool of evidence has shown that enhanced external counterpulsation (EECP) is a non-invasive, safe, low-cost, and highly beneficial therapy for patients with coronary artery disease. However, the exact mechanisms of benefit exerted by EECP therapy remain only partially understood. The favorable hemodynamic effects of EECP were previously considered as the primary mechanism of action. Nevertheless, recent advances have shed light on the shear stress-increasing effects of EECP which are vasculoprotective and anti-atherosclerotic. EECP-induced endothelial shear stress increase may lead to improvement in endothelial function and morphology, attenuation of oxidative stress and inflammation, and promotion of angiogenesis and vasculogenesis. This review summarizes evidence of the potential mechanisms contributing to the immediate and long-term benefits of EECP, from the perspective of its shear stress-increasing effects.

A novel external counterpulsation system for coronary artery disease and heart failure: pilot studies and initial clinical experiences

External counterpulsation (ECP) is a beneficial and noninvasive treatment for coronary artery disease or heart failure; however, it still has a lot of limitations. We used a novel ECP system, Compact CP, the main feature of which is the double-lumen cuff that reduces the impact of cuff inflation and the size of the air compressor. The first lumen was a contact cuff that was attached to the legs with a constant pressure (8 kPa). The second lumen was a main cuff that was inflated and deflated with a driving pressure and synchronized to the cardiac cycle. In this report, we describe the results of four pilot studies in a total number of 39 healthy volunteers and initial clinical experiences of this system in three patients. The pilot studies demonstrated that the ECP system provided significant diastolic augmentation and systolic unloading. It also achieved a satisfactory diastolic/systolic pressure ratio (1.00 ± 0.06) with a high comfort level at a driving pressure of 40 kPa. Higher pressure (50-70 kPa) increased the assist performance but decreased the comfort level. ECP was also applied with a patient with chronic refractory angina and two patients with postoperative heart failure following cardiac surgery. The clinical conditions improved. No adverse effect was observed. Our novel ECP system is safe, effective, and promising in the treatment of coronary artery disease or heart failure. Further clinical investigations are needed to support the significance of this system.

Invasive left ventricular energetics during enhanced external counterpulsation

Enhanced external counterpulsation (EECP) is a noninvasive technique that provides beneficial effects for patients with chronic, symptomatic angina pectoris. However, the direct left ventricular effects of EECP have not been studied invasively. We examined invasive right atrial pressure and left ventricular hemodynamics during EECP. Ten patients referred for diagnostic evaluation underwent left heart catheterization from the radial artery. At baseline and during EECP, left ventricular pressure and volume were measured using a micromanometer pressure-conductance catheter, along with recording of right atrial and central aortic pressures. Hemodynamics were recorded at different lower extremity cuff configuration and cuff inflation pressures. As cuff inflation pressure increased, EECP resulted in a dose-dependent increase in right atrial and aortic diastolic pressure (P < 0.0001). The increase in ventricular preload resulted in increased left ventricular volume. Maximum positive (P = 0.0003) and negative left ventricular dP/dt (P < 0.0001) increased. Left ventricular diastolic pressure decreased. There was a neutral effect on myocardial mechanical efficiency. In conclusion, EECP acutely increased right atrial and central aortic diastolic pressure. The increase in preload attenuated the reduction in left ventricular diastolic pressure resulting from systolic unloading. The increased preload counterbalanced the afterload reduction, resulting in a neutral effect on myocardial efficiency.

Does higher diastolic augmentation predict clinical benefit from enhanced external counterpulsation?: Data from the International EECP Patient Registry (IEPR)

BACKGROUND

Enhanced external counterpulsation (EECP) has been demonstrated to be an effective treatment for stable angina in patients with coronary disease. The hemodynamic effects of EECP are maximized when the ratio of diastolic to systolic pressure area is in the range of 1.5 to 2.0.

HYPOTHESIS

It is hypothesized that patients undergoing EECP who are able to achieve higher diastolic augmentation (DA) ratios may derive greater clinical benefit. This study examines the relationship between the DA ratio and clinical outcomes in patients undergoing EECP.

METHODS

We analyzed demographic, noninvasive hemodynamic, and clinical outcome data on 1,004 patients enrolled in the International EECP Patient Registry (IEPR) for treatment of chronic angina between January 1998 and August 1999. Blood pressure waveforms were recorded from finger plethysmography. Six-month clinical outcomes were obtained by telephone interview.

RESULTS

At the end of EECP treatment, 370 (37%) patients had a higher DA ratio (defined as > or = 1.5) and 634 (63%) had a lower DA ratio (defined as < 1.5). Factors associated with a lower DA ratio included age > or =65 years (p <0.001), female gender (p < 0.001), left ventricular ejection fraction < 35% (p < 0.05), hypertension (p < 0.01), prior coronary bypass surgery (p < 0.01), noncardiac vascular disease (p < 0.001), multivessel disease (p < 0.01), congestive heart failure (p < 0.01), current smoking (p < 0.01), unsuitability for further revascularization (p < 0.001), and higher baseline angina class (p < 0.001). There were no significant differences regarding diabetes mellitus, prior coronary angioplasty, prior myocardial infarction, or antianginal medication use between patients with higher or lower DA ratios. Based on a multiple logistic regression model, independent predictors of a DA ratio < 1.5 at the end of EECP included current smoking (odds ratio 3.3; 95% confidence intervals 2.0-5.4); multivessel disease (1.7; 1.3-2.3); female gender (2.2; 1.7-3.0); no prior EECP (1.9; 1.1-3.3); noncardiac vascular disease (2.3; 1.7-2.9); age > or = 65 years (1.7; 1.4-2.2), and patients not suitable for revascularization (1.6; 1.2-2.0). By the end of therapy, there were no significant differences in myocardial infarction, revascularization rates, or nitroglycerin use with respect to higher DA ratios. At 6-month follow-up, patients with higher DA had a trend toward a greater reduction in angina class compared with those with lower DA (p = 0.069). There was a significantly higher rate of unstable angina and congestive heart failure in the group not achieving higher augmentation (p < 0.05).

CONCLUSIONS

Patients who are younger, male, nonsmoking, and without multivessel coronary or noncardiac vascular disease are most likely to have higher DA with EECP. Patients with higher DA tended to have a greater reduction in angina class at 6-month follow-up compared with those with lower DA ratios. There is evidence that higher DA ratios are associated with improved short- or long-term clinical outcomes, suggesting that clinical benefit from EECP is associated with the magnitude of DA.

Enhanced external counter pulsation in treatment of refractory angina pectoris: two year outcome and baseline factors associated with treatment failure

Background

Enhanced external counter pulsation (EECP) is a non-invasive treatment option for patients with refractory angina pectoris ineligible to further traditional treatment. The aim of this study was to evaluate the effect of EECP on patients at a Scandinavian medical centre and to investigate if outcome can be predicted by analysing baseline factors.

Methods

86 consecutive patients (70 male, 16 female) were treated with EECP and followed for two years post treatment. Canadian cardiovascular society (CCS) class was analysed, and medication and adverse clinical events were researched prior to EECP, at the end of the treatment, and at six, 12 and 24 months thereafter. Patients responding to therapy by improving at least one CCS class were compared with those who failed to respond. Any differences in background factors were recorded and analysed.

Results

79% of the patients responded to therapy by improving at least one CCS class. In general, the CCS class improved by one class after EECP treatment (3.05 before versus 2.14 after treatment). A total of 61.5% of the initial responders showed sustained improvement at the 12 month follow-up while 29% presented sustained improvement after 24 months. Treatment was most effective among patients suffering from CCS class III-IV angina pectoris, while patients suffering from CCS class II angina pectoris improved transiently but failed to show sustained improvement after the 12 month follow-up. Diabetes mellitus and calcium channel antagonists were more common among the non-responders (p < 0.05).

Conclusion

This study confirms the safety and efficiency of EECP as a treatment option for patients suffering from refractory angina pectoris. The therapy is most beneficial in patients suffering from severe angina (CCS III-IV) while sustained response to therapy could not be verified among patients suffering from CCS class II angina pectoris.

Exercise capability and myocardial perfusion in chronic angina patients treated with enhanced external counterpulsation

BACKGROUND

Enhanced external counterpulsation (EECP) has been shown to improve treadmill times and myocardial perfusion. However, improvement in perfusion defects has been demonstrated only in patients exercised to the same cardiac workload on the post-EECP as the pre-EECP stress test.

HYPOTHESIS

This study was to determine the effect of EECP on exercise capacity and myocardial perfusion by comparing results of maximal exercise radionuclide testing pre- and post-EECP treatment.

METHODS

This prospective study included 25 patients with angina who had performed maximal symptom-limited exercise tolerance tests (ETT) with Bruce protocol and radionuclide perfusion single-photon emission computed tomography (SPECT) study prior to and at completion of EECP treatment.

RESULTS

After 35 h of EECP, 23 patients (93%) improved by at least one functional angina class. There is a significant improvement in their total treadmill times (357 +/- 93 to 449 +/- 97 s, p < 0.001). There was a significant change in their peak double products, from 18,891 +/- 3,939 pre-EECP to 20,464 +/- 4,305 post-EECP ETT (p < 0.03). Pre EECP, 16 patients had ST-segment depression on their initial ETT. After EECP, 13 of these patients (80%) either no longer had ST depression or had a significant increase in their time to ST depression (229 +/- 52 to 315 +/- 60 s, p < 0.001). The radionuclide perfusion scores also showed a significant reduction in ischemic segments (16.36 +/- 10.52 to 14 +/- 10.9, p < 0.05).

CONCLUSIONS

Patients treated with EECP demonstrated a reduction in angina symptoms, improvement in exercise capacity, increase in time to ST-segment depression, and decrease in perfusion defects despite performing at a higher workload.

Enhanced external counterpulsation for the treatment of angina pectoris

The treatment of refractory chronic angina pectoris presents an increasing problem for all physicians caring for patients with coronary artery disease because of the large number of individuals who have either failed multiple revascularization procedures or are not appropriate candidates for such procedures. The aim of this study was to review the safety, efficacy, and clinical applicability of a noninvasive technique (external counterpulsation) for the treatment of angina pectoris. A MEDLINE search for all English language abstracts, meeting presentations, journal articles, and reviews from 1960 through December 2005 was conducted. Of the 194 citations in the literature, 60 appeared before 1983 when the enhanced version of the technique (the one that is presently used) was first reported. Criteria for further evaluation of the 134 post-1983 citations were either (1) randomized trial, (2) observational study of at least 10 patients, or (3) investigations into possible mechanisms. Of the 134 citations, 45 were used for data extraction. Observational studies from the United States, Asia, and Europe have demonstrated improvement in symptoms, reduction in anginal episodes, better quality of life, and improved exercise performance in over 5000 patients. The only randomized study (Multicenter Study of Enhanced External Counterpulsation) confirmed these findings as well as the continuation of clinical benefits at least 1 year posttreatment. Although the mechanisms by which diastolic augmentation achieves these beneficial results are still under investigation, this is a promising noninvasive therapy in a group of patients with limited treatment options.

Effectiveness of repeat enhanced external counterpulsation for refractory angina in patients failing to complete an initial course of therapy

AIMS

This study examined the causes and results of retreatment of patients who failed to complete an initial 35-hour Enhanced External Counterpulsation (EECP) course.

METHODS AND RESULTS

Data of 2,311 successive angina patients from the International EECP Patient Registry were analyzed, 86.5% completed their EECP course (Complete cohort). Of the 13.5% patients failing to complete the initial course (Incomplete cohort), 28.3% had repeat EECP within 1 year vs. 10.1% of the Complete group. The predictors of failure to complete the initial course of EECP were: female gender, heart failure, use of angiotensin-converting enzyme inhibitors or angiotensin receptor blockers, and use of nitroglycerin. For the Complete group, 83.4% had a reduction of at least one Canadian Cardiovascular Society (CCS) class after their initial EECP course, vs. 21.7% in the Incomplete group (p < 0.001). After repeat treatment, 66.2% of the Incomplete group achieved at least one CCS class reduction vs. 69.4% of the Complete group (p = NS) undergoing retreatment. The independent predictors for those who return to successfully complete their second course were patients who stopped their first course because of clinical events, and candidacy for coronary artery bypass grafting at the time of initial treatment.

CONCLUSION

The results of retreatment of those who failed to complete their initial EECP course were comparable to those who completed their initial treatment, with similar reductions of CCS angina class.

Primer: practical approach to the selection of patients for and application of EECP

Over the past decade, the frequency of use of enhanced external counterpulsation (EECP) has increased in patients with angina, irrespective of medical therapy and coronary revascularization status. Many patients referred for EECP have one or more comorbidities that could affect this treatment's efficacy, safety, or both. By use of data from more than 8,000 patients enrolled in the International EECP Patient Registry, we provide practical guidelines for the selection and treatment of patients. We have focused on considerations for patients who have one or more of the following characteristics: age older than 75 years, diabetes, obesity, heart failure, and peripheral vascular disease. We have also reviewed outcomes and treatment recommendations for individuals with poor diastolic augmentation during treatment, for those with atrial fibrillation or pacemakers, and for those receiving anticoagulation therapy. Lastly, we examined relevant data regarding extended courses of EECP, repeat therapy, or both. While clinical studies have demonstrated the usefulness of EECP in selected patients, these guidelines permit recommendations for the extended application of this important treatment to subsets of patients excluded from clinical trials.

The immediate and long-term outcome of enhanced external counterpulsation in treatment of chronic stable refractory angina

BACKGROUND

Treatment of angina recalcitrant to conventional pharmacological therapy and revascularization remains problematic. Safe, effective and affordable treatments with high patient acceptability are desirable. Enhanced external counterpulsation (EECP) may fulfil these criteria better than many other proposed interventions.

OBJECTIVE

To examine the immediate and long-term effect of EECP in treatment of chronic stable refractory angina.

DESIGN

Prospective observational study of consecutive patients treated with EECP and follow-up for 1 year.

SETTING

Teaching hospital.

MAIN OUTCOME MEASURES

Canadian Cardiovascular Society (CCS) angina grading, weekly angina frequency and glyceryl trinitrate (GTN) use.

RESULTS

Sixty-one patients were treated with EECP and 58 completed a course of treatment. Further analysis is confined to those who completed EECP. About 52% of patients suffered from CCS III and IV angina prior to EECP. Immediately post-EECP, angina improved by at least one CCS class in 86% and by two classes in 59%. At 1-year follow-up, sustained improvement in CCS was observed in 78% of the patients. The median weekly angina frequency and GTN use were significantly reduced immediately after EECP [7 (4-14) vs. 1 (0-4) episodes per week and 7 (2-16) vs. 0 (0-2) times per week respectively, P < 0.0001; data in median (interquartile range)]. The reduction was sustained at 1-year follow-up. In 48 patients, their mean exercise time improved significantly after EECP [301 +/- 130 s vs. 379 +/- 147 s, P < 0.0001]. Major adverse treatment-related events were rare.

CONCLUSION

This study shows that for patients who fail to respond to conventional measures, a high proportion gain symptomatic benefit from EECP.

Predictors of benefit in angina patients one year after completing enhanced external counterpulsation: initial responders to treatment versus nonresponders

Enhanced external counterpulsation (EECP) has been shown to reduce Canadian Cardiovascular Society angina class. This study examines the factors that affect the reduction at 1 year, especially in patients who do not demonstrate an initial response. The data of 2,007 consecutive patients enrolled in the International EECP Patient Registry were analyzed. After 36.6 +/- 4.9 h of EECP, angina was reduced by at least one class in 82.7%. At 1 year, 35.4% of initial nonresponders and 70.6% of responders remained improved by at least one angina class and free of major adverse cardiovascular events. Multivariate predictors of 1-year benefit are initial response to treatment (odds ratio 4.5, 95% CI 3.5-5.8), baseline angina class compared with class IV (odds ratios: class I 2.1, CI 0.93-4.81; class II 0.62, CI 0.43-0.87; class III 0.80, CI 0.62-1.01) and no history of congestive heart failure (odds ratio 1.41, CI 1.14-1.74).

Enhanced external counterpulsation: a new technique to augment renal function in liver cirrhosis

BACKGROUND

Advanced liver cirrhosis is characterized by cardiovascular changes, such as low arterial blood pressure, peripheral vasodilation and renal vasoconstriction. As a consequence, renal hypoperfusion, impaired diuresis and natriuresis and eventual hepatorenal syndrome may ensue. Previous studies using head-out water immersion to increase central blood volume have demonstrated the functional nature of the renal abnormalities. Enhanced external counterpulsation (EECP) is a new non-invasive cardiac assist device to augment diastolic blood pressure by electrocardiogram-triggered diastolic inflation and deflation of cuffs wrapped around the lower extremities. We investigated whether EECP would improve renal dysfunction of liver cirrhosis.

METHODS

Twelve healthy controls and 19 patients with liver cirrhosis were observed during 2 h of baseline followed by 2 h of EECP. The following parameters of renal and cardiovascular function were measured: renal plasma flow by para-aminohippurate clearance, glomerular filtration rate (GFR) by inulin clearance, urine flow rate, urinary excretion rates of sodium and chloride, mean arterial blood pressure (MAP), renal vascular resistance (RVR) and plasma concentrations of renin, atrial natriuretic peptide (ANP), endothelin-1, antidiuretic hormone, epinephrine and N-epinephrine.

RESULTS

EECP was well tolerated by healthy controls and cirrhotic patients alike. EECP increased MAP (cirrhotic patients: from 74+/-18 to 88+/-20 mmHg, P<0.01; controls: from 89+/-8 to 94+/-5 mmHg, P = NS) and ANP (cirrhotic patients: from 23+/-18 to 30+/-20 ng/l, P<0.05; controls: from 11+/-4 to 16+/-5 ng/l, P<0.01). The plasma renin concentration decreased (cirrhotic patients: from 98+/-98 to 58+/-57 ng/l, P<0.01; controls: from 4.6+/-1.6 to 3.4+/-1.1 ng/l, P<0.01). This was associated with improvement of the urinary flow rate (cirrhotic patients: from 3.6+/-1.8 to 4.6+/-0.7 ml/min, P<0.05; controls: from 1.8+/-1.5 to 2.8+/-1.9 ml/min, P<0.05), as well as of the sodium and chloride excretion rates in both groups. However, in contrast to healthy controls, GFR and renal plasma flow in cirrhotic patients failed to rise significantly. Renal vascular resistance fell numerically in healthy controls (68+/-5 vs 55+/-4 mmHg . min/l; P = NS). In contrast, RVR showed a significant increase by approximately 20% in cirrhosis (67+/-4 vs 80+/-8 mmHg . min/l; P<0.05). Endothelin-1 levels fell in controls (0.38+/-0.42 vs 0.31+/-0.35; P<0.05), whereas they remained statistically unchanged in cirrhotic patients. Epinephrine, N-epinephrine and vasopressin were not altered by EECP in either group.

CONCLUSIONS

EECP is an effective procedure to augment renal excretory function in healthy volunteers as well as in patients with cirrhosis. In healthy volunteers, GFR and renal plasma flow increased during EECP. In contrast, these parameters remained unchanged in the patients and their renal vascular resistance increased during EECP. Therefore, EECP improves diuresis, but does not influence the vasoconstrictive dysregulation of the kidneys in liver cirrhosis.

Enhanced external counterpulsation does not compromise cerebral autoregulation

OBJECTIVES

Enhanced external counterpulsation (EECP) rhythmically augments blood pressure (BP) by diastolic lower-body compression. Recently, we showed decreased mean cerebral blood flow velocity (CBFVmean) in young healthy persons during EECP, but unchanged CBFVmean in atherosclerotic patients. In this study, we assessed EECP effects on dynamic cerebral autoregulation (CA).

MATERIAL & METHODS

In 23 healthy persons and 15 atherosclerotic patients we monitored heart rate (HR), mean BP (BPmean) and CBFVmean before and during 5 min EECP. We analyzed spectral powers of HR, BPmean and CBFVmean in the low (LF: 0.04-0.15 Hz) and high (HF: 0.15-0.5 Hz) frequency ranges to determine CA from the LF-transfer function gain and phase shift between BPmean and CBFVmean oscillations.

RESULTS

EECP increased HR and BPmean, while transfer function gain and phase shift remained stable.

CONCLUSIONS

Stable gain and phase values suggest that EECP does not compromise CA and, therefore, does not seem to bear cerebrovascular risks.

Effectiveness of enhanced external counterpulsation in patients with left main disease and angina

BACKGROUND

Enhanced external counterpulsation (EECP) is a noninvasive device that uses three pairs of sequentially inflated pneumatic cuffs applied to the lower extremities and synchronized with the heart beat to provide diastolic augmentation, increase coronary blood pressure and flow, venous return and cardiac output, and decrease afterload.

HYPOTHESIS

This study examines the safety and effectiveness of EECP therapy in patients with significant left main coronary artery disease (LMD).

METHODS

In all, 2,861 patients enrolled in the International EECP Patient Registry (IEPR) were divided into three groups, those without LMD (n = 2,377), those with LMD and prior CABG (n = 431), and those with unbypassed LMD (n = 53).

RESULTS

Patients with LMD, with or without prior CABG, were significantly more likely to have triple-vessel disease (98.1 and 88.7%, respectively) than patients without LMD (41.9%). Post-EECP, 74% without LMD, 75% with LMD with prior CABG, and 65% with unbypassed LMD improved their Canadian Cardiovascular Society (CCS) angina by at least one class (p = NS). There were no differences in the mean decrease in weekly angina episodes (7.1 vs. 8.0 vs. 7.6) and in the mean frequency of weekly nitroglycerin use (6.6 vs. 8.1 vs. 8.9). At 6-month follow-up, the CCS class improved further in all three groups, and there was a further reduction in mean weekly angina episodes (4.7 vs. 4.6 vs. 5.3) and nitroglycerin use (6.5 vs. 6.8 vs. 8.2). Kaplan-Meier life table analysis 8 months after starting EECP demonstrated a major cardiovascular event rate of 11.2% in patients without LMD, 15.6% in LMD with CABG, and 24.3% in LMD without prior CABG. Late mortality in unbypassed LMD was 13.2% (confidence interval [CI] 3.3-23.1) versus 4.8% (CI 2.7-7.1) in LMD with CABG, and 2.8% (CI 2.1-3.5) without LMD (p = 0.0039 by log-rank test).

CONCLUSION

Enhanced external counterpulsation is equally effective in relieving angina in patients with or without LMD. However, the significantly increased late mortality in patients with LMD without prior CABG suggests that early revascularization should be considered in these patients.

ACCELERATED REPERFUSION OF POORLY PERFUSED RETINAL AREAS IN CENTRAL RETINAL ARTERY OCCLUSION AND BRANCH RETINAL ARTERY OCCLUSION AFTER A SHORT TREATMENT WITH ENHANCED EXTERNAL COUNTERPULSATION

BACKGROUND

To date, no satisfactory therapy has become available for patients with acute central retinal artery occlusion (CRAO) or branch retinal artery occlusion (BRAO). Enhanced external counterpulsation (EECP) is a new noninvasive procedure that increases perfusion of inner organs. In the current study, the authors measured the impact of EECP on reperfusion in ischemic retinal tissue.

METHODS

In a prospective, randomized study, 20 patients with CRAO or BRAO were included. Ten patients were given hemodilution therapy and 2 hours of EECP, and 10 patients were given regular hemodilution therapy only. Quantification of changes in retinal perfusion was carried out by means of scanning laser Doppler flowmetry (in arbitrary units).

RESULTS

Enhanced external counterpulsation caused no observable adverse events. A significant increase in perfusion occurred immediately after EECP in the ischemic retinal areas (57 +/- 19 arbitrary units versus 99 +/- 14 arbitrary units). In contrast, no change was measured in the group not treated with EECP (83 +/- 19 arbitrary units versus 89 +/- 44 arbitrary units). Forty-eight hours later, a significant increase in perfusion could be shown in the ischemic retina of both groups, and no significant difference of perfusion was found between the two groups any longer.

CONCLUSION

The current study suggests that EECP could be a clinically useful and safe procedure in patients with CRAO or BRAO to accelerate recovery of perfusion in ischemic retinal areas.

Enhanced external counterpulsation improves skin oxygenation and perfusion

BACKGROUND

Enhanced external counterpulsation (EECP) augments diastolic and reduces systolic blood pressures. Enhanced external counterpulsation has been shown to improve blood flow in various organ systems. Beneficial effects on skin perfusion might allow EECP to be used in patients with skin malperfusion problems. This study was performed to assess acute effects of EECP on superficial skin blood flow, transdermal oxygen and carbon dioxide pressures.

MATERIALS AND METHODS

We monitored heart rate, blood pressure, transdermal blood flow as well as oxygen and carbon dioxide pressures in 23 young, healthy persons (28 +/- 4 years) and 15 older patients (64 +/- 7 years) with coronary artery disease before, during and 3 min after 5 min EECP. Friedman test was used to compare the results of 90-s epochs before, during and after EECP. Significance was set at P < 0.05.

RESULTS

Enhanced external counterpulsation increased heart rate and mean blood pressure. During EECP, transdermal oxygen pressure and concentration of moving blood cells increased while transdermal carbon dioxide pressure and velocity of moving blood cells decreased significantly in both groups. After EECP, transdermal carbon dioxide pressure was still reduced while the other parameters returned to baseline values.

CONCLUSIONS

Improved skin oxygenation and carbon dioxide clearance during EECP seem to result from the increased concentration and reduced flow velocity, i.e. prolonged contact time, of erythrocytes. The increased concentration of moving blood cells and the decreased velocity of moving blood cells at both tested skin sites indicate peripheral vasodilatation.

Successful treatment of symptomatic coronary endothelial dysfunction with enhanced external counterpulsation

Enhanced external counterpulsation (EECP) is a valuable therapeutic option for patients with coronary artery disease and refractory angina. Although the exact mechanisms by which this technique exerts favorable effects remain unclear, improvement in endothelial function is considered a potential mechanism contributing to the clinical benefit associated with EECP. We describe a young woman with severely symptomatic coronary endothelial dysfunction in the absence of obstructive coronary artery disease who experienced a dramatic and sustained reduction in symptoms in response to a standard 35-hour course of EECP.

Practicability and limitations of enhanced external counterpulsation as an additional treatment for angina

BACKGROUND

An increasing number of clinical studies indicates reduction of angina and myocardial ischemia by enhanced external counterpulsation (EECP) therapy. However, given the wide range of contraindications and the long duration of treatment, eligibility and practicality issues have not been addressed systematically.

HYPOTHESIS

Of all candidates for EECP (patients with drug-refractory angina without possibility of revascularization), the majority either have contraindications or have practical problems complying with the time demands that this therapy imposes. In the rest, EECP leads to satisfactory results.

METHODS

During 18 months, every consecutive patient with angina despite medical and interventional therapy was evaluated for EECP at one center. Treated patients underwent a bicycle exercise test and perfusion imaging before and after the standard course of 35 h of EECP. In addition, patients were asked about frequency of angina and nitroglycerin usage before and after EECP, and all patients filled out a final questionnaire 1 year after the end of therapy.

RESULTS

Overall, 48 patients were considered candidates for EECP. Of these, 24 were excluded for medical reasons: poor ejection fraction (4), peripheral artery disease (4), anticoagulation (4), and atrial fibrillation (3). Eight further patients declined EECP for lack of time or accommodation. Another 3 of the 16 remaining patients dropped out because of side effects. In the 13 patients who finished the treatment course, weekly anginal episodes were reduced by 48% (p < 0.05), on-demand nitroglycerin puffs were reduced by 51% (p < 0.05), work capacity was improved by 22% (p < 0.05), and the number of reversible perfusion defects in perfusion scans decreased nonsignificantly (-28%). However, 4 of 13 treated patients determined 1 year later that the detriment of loss of time exceeded the benefits of EECP.

CONCLUSION

Similar to previous reports, our study confirms the reduction of angina and improvement of work capacity after EECP. However, using established contraindications, approximately two-thirds of patients considered to be candidates had to be excluded, and one-third of the treated patients regarded EECP therapy retrospectively as too time consuming.

Analysis of baseline factors associated with reduction in chest pain in patients with angina pectoris treated by enhanced external counterpulsation

Data from the International Enhanced External Counterpulsation (EECP) Patient Registry were analyzed to determine which patient characteristics influence improvement in angina class with EECP treatment. Patients with severely disabling angina at baseline, men, and those without a history of smoking are more likely to improve their angina class after EECP, whereas those with diabetes mellitus, prior bypass surgery, and heart failure were less likely to benefit.

Enhanced external counterpulsation for refractory angina pectoris

Enhanced external counterpulsation (EECP) is a non-invasive outpatient treatment used for angina pectoris. In patients with intractable angina refractory to aggressive surgical and medical treatment, several novel strategies are considered including EECP, transmural laser revascularisation, and spinal cord stimulation. EECP produces an acute haemodynamic effect that is presumed to be similar to that produced by the invasive intra-aortic balloon pump. By applying a series of compressive cuffs sequentially from the calves to the thigh muscles upon diastole and rapidly deflating the cuffs in early systole, an increase in diastolic and decrease in systolic pressure is created. Although data indicate improvement in angina in patients undergoing EECP, the role of EECP in the treatment of angina pectoris has not yet been well defined. At present, EECP use should be limited to patients with debilitating (functional class III and IV) refractory angina pectoris who are not candidates for revascularisation, are symptomatic despite being on maximal antianginal pharmacotherapy, and have no contraindications to EECP use.

Enhanced external counterpulsation for ischemic heart disease: what's behind the curtain?

Enhanced external counterpulsation (EECP) has been shown to reduce angina and to improve objective measures of myocardial ischemia in patients with refractory angina. Prospective clinical studies and large treatment registries suggest that a course of EECP is associated with prolongation of the time to exercise-induced ST-segment depression and resolution of myocardial perfusion defects, as well as with enhanced exercise tolerance and quality of life. With a growing knowledge base supporting the safety and beneficial clinical effects associated with EECP, this therapy can be considered a valuable treatment option, particularly in patients who have exhausted traditional revascularization methods and yet remain symptomatic despite optimal medical care. However, although the concept of external counterpulsation was introduced almost four decades ago, and despite growing evidence supporting the clinical benefit and safety of this therapeutic modality, little is firmly established regarding the mechanisms responsible for the beneficial effects associated with this technique. Suggested mechanisms contributing to the clinical benefit of EECP include improvement in endothelial function, promotion of coronary collateralization, enhancement of ventricular function, peripheral effects similar to those observed with regular physical exercise, and nonspecific placebo effects. This review summarizes the current evidence for a contribution of these mechanisms to the clinical benefit associated with EECP.

Changes of cerebral blood flow velocities during enhanced external counterpulsation

OBJECTIVES

Intra-aortic counterpulsation is the most frequently used cardiac assist device. However, there are only few studies of the effects of counterpulsation on cerebral blood flow and these report conflicting outcomes. The new enhanced external counterpulsation (EECP) technique reproduces non-invasively the effects of intra-aortic counterpulsation. In this study, we evaluated effects of EECP on blood pressure (BP) and on cerebral flow velocity (CBFV).

SUBJECTS AND METHODS

Twenty-three healthy controls and 15 atherosclerotic patients each underwent a 5-min session of EECP. Before, during and after EECP we monitored heart rate, beat-to-beat radial artery BP and CBFV.

RESULTS

EECP induced a second increase in BP and CBFV during diastole with a significant increase of mean BP and a decrease of systolic BP in patients and controls. Mean CBFV increased in both groups during the first 5 s of EECP. After 3 min of EECP, diastolic CBFV was still higher than at baseline, but systolic CBVF was lower than at baseline; mean CBFV was as low as before EECP in the patients and lower than the baseline values in the controls. Three minutes after ending EECP, mean and systolic BP were lower in the patients than the corresponding baseline values. Otherwise, CBFV and BP values did not differ from baseline in patients and controls.

CONCLUSION

Cerebral autoregulation ensures the constancy of cerebral blood flow even though EECP creates marked systemic changes. In the patients, the decrease of BP after EECP with maintained CBFV indicates an improved BPCBFV relation and a more economic autoregulation.

Enhanced external counterpulsation improves endothelial function in patients with symptomatic coronary artery disease

OBJECTIVES

The goal of this study was to examine the effect of enhanced external counterpulsation (EECP) on endothelial function.

BACKGROUND

Enhanced external counterpulsation improves symptoms and exercise tolerance in patients with symptomatic coronary artery disease (CAD). However, the exact mechanisms by which this technique exerts its clinical benefit are unclear.

METHODS

Reactive hyperemia-peripheral arterial tonometry (RH-PAT), a noninvasive method to assess peripheral endothelial function by measuring reactive hyperemic response in the finger, was performed in 23 patients with refractory angina undergoing a 35-h course of EECP. In each patient RH-PAT measurements were performed before and after the first, at midcourse, and the last EECP session. In addition, RH-PAT response was assessed one month after completion of EECP therapy; RH-PAT index, a measure of reactive hyperemia, was calculated as the ratio of the digital pulse volume during reactive hyperemia divided by that at rest.

RESULTS

Enhanced external counterpulsation led to symptomatic improvement (>/=1 Canadian Cardiovascular Society class) in 17 (74%) patients; EECP was associated with a significant immediate increase in average RH-PAT index after each treatment (p < 0.05). In addition, average RH-PAT index at one-month follow-up was significantly higher than that before EECP therapy (p < 0.05). When patients were divided by their clinical response, RH-PAT index at one-month follow-up increased only in those patients who experienced clinical benefit.

CONCLUSIONS

Enhanced external counterpulsation enhances peripheral endothelial function with beneficial effects persisting at one-month follow-up in patients with a positive clinical response. This suggests that improvement in endothelial function may contribute to the clinical benefit of EECP in patients with symptomatic CAD.

Left ventricular systolic unloading and augmentation of intracoronary pressure and Doppler flow during enhanced external counterpulsation

BACKGROUND

Enhanced external counterpulsation (EECP) is a noninvasive, pneumatic technique that provides beneficial effects for patients with chronic, symptomatic angina pectoris. However, the physiological effects of EECP have not been studied directly. We examined intracoronary and left ventricular hemodynamics in the cardiac catheterization laboratory during EECP.

METHODS AND RESULTS

Ten patients referred for diagnostic evaluation underwent left heart catheterization and coronary angiography from the radial artery. At baseline and then during EECP, central aortic pressure, intracoronary pressure, and intracoronary Doppler flow velocity were measured using a coronary catheter, a sensor-tipped high-fidelity pressure guidewire, and a Doppler flow guidewire, respectively. Similar to changes in aortic pressure, EECP resulted in a dramatic increase in diastolic (71+/-10 mm Hg at baseline to 137+/-21 mm Hg during EECP; +93%; P<0.0001) and mean intracoronary pressures (88+/-9 to 102+/-16 mm Hg; +16%; P=0.006) with a decrease in systolic pressure (116+/-20 to 99+/-26 mm Hg; -15%; P=0.002). The intracoronary Doppler measure of average peak velocity increased from 11+/-5 cm/s at baseline to 23+/-5 cm/s during EECP (+109%; P=0.001). The TIMI frame count, a quantitative angiographic measure of coronary flow, showed a 28% increase in coronary flow during EECP compared with baseline (P=0.001).

CONCLUSIONS

EECP unequivocally and significantly increases diastolic and mean pressures and reduces systolic pressure in the central aorta and the coronary artery. Coronary artery flow, determined by both Doppler and angiographic techniques, is increased during EECP. The combined effects of systolic unloading and increased coronary perfusion pressure provide evidence that EECP may serve as a potential mechanical assist device.

Enhanced external counterpulsation in patients with heart failure: a multicenter feasibility study

To assess the feasibility of using enhanced external counterpulsation to treat patients with heart failure, 26 patients with stable heart failure (New York Heart Association classes II-III), with a left ventricular ejection fraction at or below 35%, and without fluid overload, were treated with enhanced external counterpulsation (1 hour daily, 5 days a week, to a total of 35 hours). Patients were followed for 6 months after completing the course of enhanced external counterpulsation. The primary parameter was safety as reflected by adverse events or by changes in laboratory parameters. Secondary end points included changes in exercise capacity and quality of life. There were no clinically significant problems associated with the administration of enhanced external counterpulsation. Significant improvements were seen in exercise capacity (peak oxygen uptake and exercise duration), and in quality of life assessments, at 1 week and 6 months after the course of enhanced external counterpulsation. This study suggests that enhanced external counterpulsation is safe and well tolerated in patients with stable heart failure, and that a randomized, controlled study of enhanced external counterpulsation in these patients is warranted.

Effects of enhanced external counterpulsation on stress radionuclide coronary perfusion and exercise capacity in chronic stable angina pectoris

Enhanced external counterpulsation (EECP) is an effective noninvasive treatment for patients with coronary artery disease (CAD). EECP has been demonstrated to improve anginal class and time to ST-segment depression during exercise stress testing. This study assesses the efficacy of EECP in improving stress-induced myocardial ischemia using radionuclide perfusion treadmill stress tests (RPSTs). The international study group enrolled patients from 7 centers with chronic stable angina pectoris and a baseline ischemic pre-EECP RPST. Patients' demographic and clinical characteristics were recorded. A baseline pre-EECP maximal RPST was performed within 1 month before EECP treatment. The results were compared with a follow-up RPST performed within 6 months of completion of a 35-hour course of EECP. Four centers performed post-EECP RPST to the same level of exercise as pre-EECP, whereas 3 centers performed maximal RPST post-EECP. The study enrolled 175 patients (155 men and 20 women). Improvement in angina, defined by > or =1 Canadian Cardiovascular Society angina class change, was reported in 85% of patients. In the centers performing the same level of exercise, 81 of 97 patients (83%) had significant improvement in RPST perfusion images. Patients who underwent maximal RPST revealed improvement in exercise duration (6.61 +/- 1.88 pre-EECP vs 7.41 +/- 2.03 minutes post-EECP, p <0.0001); 42 of the 78 patients (54%) in this group showed significant improvement in RPST perfusion images. Thus, EECP was effective in improving stress myocardial perfusion in patients with chronic stable angina at both comparable (baseline) and at maximal exercise levels.

Acute hemodynamic effects and angina improvement with enhanced external counterpulsation

Enhanced external counterpulsation (EECP) is an effective noninvasive treatment for coronary artery disease. The mechanism of action is felt to be hemodynamic. The complex hemodynamic effects have been simply quantified by calculating a previously described effectiveness ratio (ER). The EECP Clinical Consortium, a clinical registry of 37 centers, prospectively enrolled 395 chronic stable angina patients (79 women, 316 men, mean age 66 years) to examine the relation of the ER to posttreatment improvement in Canadian Cardiovascular Society angina class (CCS). Women and the elderly underwent planned subgroup analysis. The ER was calculated during the first and last hours of a 35-hour course of EECP treatment. After EECP, CCS improved by at least 1 class in 88% of patients, 87% of men and 92% of women (p = NS), and in 89% of patients < or = 66 years and 88% of patients > 66 years old (p = NS). The initial and final ER were similar in patients with and without improvement in CCS. Significant first-hour ER differences were seen between men and women (0.96 +/- 0.03 vs 0.76 +/- 0.04, p<0.005), and between ages < or = 66 and > 66 years old (1.04 +/- 0.04 vs 0.81 +/- 0.03, p<0.0001). However, all subgroups responded equally well to EECP treatment. EECP is effective in improving CCS in chronic stable angina patients; it has comparable effects in men and women and across a broad range of ages. The hemodynamic effect of EECP (ER) does not predict improvement in CCS and may indicate that other factors, such as neurohormonal changes, may have a significant role in mediating the observed EECP benefits.

Psychosocial effects of enhanced external counterpulsation in the angina patient: a second study

Enhanced external counterpulsation (EECP) is a noninvasive technique that has shown promise in the treatment of ischemic coronary artery disease. Patients undergoing EECP were tested for alterations in psychosocial state associated with treatment. Overall perception of health and quality of life improved with EECP. There was also significant improvement in levels of depression, anxiety, and somatization but no change in levels of anger or hostility. On most measures, change was more significant for subjects who showed objective evidence of resolution of ischemia. Given the known predictive relationship between depression and mortality from cardiac disease, the improvement in depression scores through EECP indicates a finding of potential importance that may warrant further study in future research.

Comparison of hemodynamic effects of enhanced external counterpulsation and intra-aortic balloon pumping in patients with acute myocardial infarction

This study compared the hemodynamic effects of enhanced external counterpulsation and intra-aortic counterpulsation in patients with acute myocardial infarction. Results demonstrated similarity between these 2 methods, except enhanced external counterpulsation had a transient effect of increasing right atrial pressure, pulmonary capillary wedge pressure, and cardiac index.