American Heart Journal
Volume 141, Issue 6 , Pages 889-892, June 2001

Aortic counterpulsation in acute myocardial infarction: Physiologically important but does the patient benefit?☆☆☆★

Chapel Hill, NC, and New York, NY

From the aDivision of Cardiology, University of North Carolina at Chapel Hill, NC, and bSt Luke’s-Roosevelt Hospital Center, Columbia University, New York, NY

Received 18 January 2001; accepted 16 February 2001.

Article Outline

 

See related article on page 933 .

Aortic counterpulsation (intra-aortic balloon pump [IABP]) was introduced in the 1970s as a means for supporting patients undergoing surgical revascularization.1 Initial experience documented that this device had important physiologic effects including improvement in cardiac function and diastolic blood pressure and a reduction in systemic acidosis.2 More recently, several investigators have also shown enhanced coronary perfusion with IABP,3 particularly among patients having percutaneous transluminal coronary angioplasty during cardiogenic shock.4 However, this impressive physiologic profile has not been followed by equally important randomized clinical trial data. In the early 1980s two smaller randomized trials failed to show any benefit of IABP compared with control therapy on infarct size or left ventricular function in patients with cardiogenic shock.5, 6 Nevertheless, anecdotal experience with IABP suggested that this therapy could have beneficial effects to warrant it as a class I recommendation by the American Heart Association (AHA)/American College of Cardiology (ACC) Guidelines for the management of acute myocardial infarction for patients with cardiogenic shock.7

Observations from large randomized clinical trials and registries have provided invaluable information on the use and outcomes with IABP among patients with cardiogenic shock. Despite the AHA/ACC guidelines, the use of IABP is infrequent among patients with cardiogenic shock. In the Global Utilization of Streptokinase and Tissue Plasminogen Activator for Occluded Coronary Arteries (GUSTO I) trial, carried out between 1991 and 1993, IABP was used in only 35% of patients with cardiogenic shock in the United States.8 This improved somewhat to 47% in the GUSTO III trial carried out between 1995 and 1997.8 The IABP was more frequently used in patients treated in the United States compared with other countries, and there was suggestion that the higher use in the United States was associated with a lower mortality rate.9 In the registry accompanying the Should We Emergently Revascularize Occluded Coronaries for Cardiogenic Shock? (SHOCK) trial, with predominantly centers in the United States, an IABP was used in 51% of patients.10

Nonrandomized clinical studies have uniformly shown a benefit associated with IABP for patients with cardiogenic shock.9, 10, 11, 12, 13, 14 These are summarized in Table I. However, the patients receiving IABP are in general younger, have fewer comorbid illnesses, and are more aggressively treated with cardiac catheterization and revascularization compared with patients not treated with IABP.9, 10 In the clinical setting of substantial underuse of IABP and recognizing the difficulties in adjusting for biases in the observational series, two randomized trials were started to more conclusively ascertain the treatment effect of IABP in high-risk patients with acute myocardial infarction. Neither study was able to achieve the target enrollment and only one has reported some preliminary outcome data.15, 16

Table I. In-hospital mortality in registries with aortic counterpulsation in cardiogenic shock
StudyIABPControlP value
Moulopoulos et al11 (n = 49)*69%100%NA
Waksman et al12 (n = 85)*54%62%P < .001
Kovack et al13 (n = 46)†33%68%P = .019
GUSTO-I9 (n = 310)† (IABP within 24 h)47%60%P = .06
GUSTO-I and III9 (n = 3,396)† (all shock patients)45%58%P = .001
SHOCK Registry10 (n = 854)†50%70%P < .0001
NRMI-214 (n = 23,180)*48%54%P < .01
*In-hospital mortality. †30-day mortality.

In this issue of the Journal, Barron and colleagues report the largest experience with IABP in cardiogenic shock. The series comes from the Genentech-sponsored National Registry of Myocardial Infarction (NRMI) that was initiated in 1990.14 In the second NRMI registry (1994-1998), 23,180 patients were identified with cardiogenic shock in which IABP was used in 7268 (31%). The overall mortality was 70%, which is consistent with other community registries in the United States.17 Patients who were treated with IABP were a healthier cohort as evidenced by younger age (10 years on average) and lower rates of diabetes mellitus, heart failure, or stroke before admission. The majority of patients who did receive IABP were more likely to have undergone reperfusion therapy compared with those who did not (thrombolysis 30% vs 22% and primary angioplasty 28% vs 6%). The in-hospital mortality rate was significantly lower among patients receiving IABP and thrombolysis in cardiogenic shock compared with those receiving thrombolysis alone (67% vs 49%). This effect (P < .01) was maintained after adjustment for the differences in baseline clinical characteristics of the patients. On the other hand, patients treated with primary angioplasty had a significantly lower mortality rate of 42%, but IABP use was not associated with any benefit in this group (47% mortality). There was also a statistical significant interaction between the reperfusion strategy used, IABP use, and mortality, suggesting a differential treatment effect of IABP.

The outcome from this registry has several important implications for the management of cardiogenic shock. First, it underscores the significant underuse of IABP that exists despite the guidelines. The low use is consistent with the findings from the GUSTO trials and the Worcester community, where 36% and 25%, respectively, of patients with cardiogenic shock had IABP inserted.9, 17 Second, as documented in the NRMI experience, the use of IABP appears linked to the availability of expertise with cardiac catheterization and angioplasty; only 6% of patients not receiving IABP were treated with primary angioplasty whereas 72% had no reperfusion therapy at all. However, Kovack et al13 have documented that survival can be improved with IABP use in a community hospital setting, as shown in Table I. Their study has also shown that early IABP insertion facilitates transport to a tertiary care center, where revascularization can be performed. The importance of this “stabilize, treat, and transfer” concept is further underscored by the substantial reduction in 1-year mortality observed in the randomized SHOCK trial.18 In this study, where 55% of patients where transferred to a tertiary care center for revascularization, the patients randomized to early revascularization had a 53% mortality rate compared with 66% among those treated with initial medical stabilization. Both groups were supported with IABP (86%) and the latter group received thrombolysis (63%) and subsequent revascularization (25%). The benefit of rapid revascularization after shock onset was the same for transferred patients and those admitted directly to the tertiary care facility. Importantly, this more aggressive approach to cardiogenic shock, as supported by the findings from a randomized trial, appears to also have an impact in the community. Observations from the Worcester community have identified that the increasing use of IABP and revascularization are associated with improved cardiogenic shock survival.17 During a 22-year period, there was a substantial increase in IABP use from 5% to 42%, angioplasty (0%-28%), and coronary artery bypass grafting (0%-14%), with a 23% relative fall in mortality.17 These findings would suggest that more physicians should receive formal training in IABP use and therapy so that this form of therapy could be available in all acute care hospitals. If this is coupled with rapid transfer to regional centers that specialize in the management of cardiogenic shock, similar to regional trauma care centers, there could be a substantial number of lives saved annually.

Third, there was a substantial reduction in mortality among patients treated with IABP and thrombolysis. It is postulated that the reason for low reperfusion rates with fibrinolytic therapy among patients with cardiogenic shock is the lack of perfusion pressure in the infarct-related artery.19, 20 Gurbel et al21 have documented that IABP can enhance coronary flow after thrombolysis, whereas Gu et al20 and Prewitt et al22 found that the rate of clot lysis was enhanced with increasing diastolic blood pressure (by IABP or pharmacologically) in animal models. Although there is no confirmation of this in humans, there is indirect evidence of enhanced coronary perfusion with IABP with use of Doppler flow wires.4 On the basis of the available physiologic data and observational information as shown in Table I, it would appear that using IABP in conjunction with thrombolysis could enhance reperfusion and clinical outcome in cardiogenic shock, particularly in hospitals that do not perform acute myocardial infarction angioplasty.

It is of note that patients who were in cardiogenic shock on arrival to the hospital were less likely to receive an IABP (odds ratio [OR] 0.63, 95% confidence interval 0.59-0.68) in the NRMI experience. This was also noted in the GUSTO trial, where it was partly explained by the fact that the majority of patients who arrived in shock and did not receive an IABP died within 7 hours of hospital arrival.23 Recent observations both from community hospitals and clinical trials have suggested that IABP can be inserted with the aid of fluoroscopy in the emergency department in the majority of patients within 3 hours of hospital arrival.15 Thus it is possible to quickly stabilize the patients if critical pathways are developed for cardiogenic shock in acute myocardial infarction. This is the concept that is central to the “golden hour” concept in trauma care. This approach has been successful for establishing reperfusion therapy in acute myocardial infarction by use of thrombolysis in a timely manner.24 Similar pathways need to be developed for cardiogenic shock that incorporates rapid stabilization with IABP and emergency early mechanical reperfusion therapies.

Among patients in cardiogenic shock treated with primary angioplasty, there was a statistically higher mortality with IABP (47% vs 42%; OR 1.27, P < .01). It is not clear why a higher mortality rate was observed in this cohort in cardiogenic shock. It has previously been documented that patients receiving IABP have more major bleeding complications after thrombolysis.25 No information on bleeding is available in the NRMI report, but in randomized trials of IABP among patients without cardiogenic shock treated with acute MI angioplasty no increase in major bleeding or vascular complications was observed.26, 27 It would seem that this is not the cause in this study. It is likely that statistical adjustments for the differences in baseline characteristics could not fully adjust for the healthier status of 33% of patients with cardiogenic shock treated with primary angioplasty who did not receive an IABP. Cardiac index and pulmonary capillary wedge pressure are highly correlated with outcome and were not adjusted for in this study. IABPs are typically used in patients with greater hemodynamic instability. Furthermore, there is no information on the timing of insertion of IABP. Previous randomized trials of IABP in high-risk patients without cardiogenic shock have suggested a lower morbidity, particularly among the patients with several high-risk features.28, 29 These studies were too small to be able to address mortality, but directionally they favored a better outcome with IABP. One observational study in cardiogenic shock from Duke University documented a survival benefit among patients treated with IABP and angioplasty.30 The NRMI experience should not deter the use of IABP during primary angioplasty because the beneficial effect of early revascularization on 6- and 12-month survival in the SHOCK trial was observed in the context of most patients receiving IABP. For patients who remain hemodynamically unstable, IABP offers the angioplasty operator the chance to have a less complicated angioplasty procedure with a higher technical success.31

The use of IABP has evolved greatly since the 1970s. Although there are few randomized trials that clearly ascertain the relative treatment effect, there is a wealth of physiologic and outcomes data to support the use of early IABP therapy in cardiogenic shock. Randomized trials of IABP in cardiogenic shock are clearly needed, but several have been attempted but have not been completed because of physician bias and difficulties in obtaining consent among critically ill patients. The observation by Barron and colleagues strengthens the case for more “proactive” care among patients with cardiogenic shock. The ability to implement the benefits of a “stabilize with IABP, treat with reperfusion, and transfer for complete revascularization” is now only limited by a lack of an organized health care system that can deliver these facets to improve outcomes for patients with cardiogenic shock. We can learn from our surgical colleagues and imitate the trauma care approach for cardiogenic shock. The golden-hour concept for cardiogenic shock has yet to be realized, but it will be “golden” for our patients when more cardiologists take on this approach.

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References 

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☆ E. M. O. has served as ad hoc consultant and has received research grants from Datascope Corp and Genentech Corp.

☆☆ Reprint requests: E. Magnus Ohman, MD, Division of Cardiology, University of North Carolina at Chapel Hill, 324 Burnett-Womack Bldg, CB #7075, Chapel Hill, NC 27599. E-mail: Ohman001@mc.duke.edu

★ Am Heart J 2001;141:889-92.

PII: S0002-8703(01)35227-4

doi:10.1067/mhj.2001.115296

Refers to article:

  • The use of intra-aortic balloon counterpulsation in patients with cardiogenic shock complicating acute myocardial infarction: Data from the National Registry of Myocardial Infarction 2

    Hal V. Barron, Nathan R. Every, Lori S. Parsons, Brad Angeja, Robert J. Goldberg, Joel M. Gore, Tony M. Chou, for the Investigators in the National Registry of Myocardial Infarction 2
    American Heart Journal June 2001 (Vol. 141, Issue 6, Pages 933-939)

American Heart Journal
Volume 141, Issue 6 , Pages 889-892, June 2001

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