Abstract
Although the use of percutaneous circulatory assist devices is gaining increasing acceptance as an adjunct to percutaneous coronary intervention (PCI) in patients with cardiogenic shock, their role in patients with acute myocardial infarction (MI) without hemodynamic compromise and elective high-risk PCI remains controversial. This is reflected by the lack of formal recommendations by the international bodies regarding the use of such devices outside the setting of cardiogenic shock. The purpose of this article was to review the current evidence for the use of these devices in patients presenting with acute MI without cardiogenic shock and in those undergoing elective high-risk PCI.
1
Introduction
Acute left ventricular (LV) failure can accompany both acute myocardial infarction (MI) and percutaneous coronary intervention (PCI). This in turn is accompanied by hypoperfusion of vital organs and initiation of a catastrophic downward spiral leading to multi-organ failure and, ultimately, death. Prophylactic or bailout percutaneous circulatory assist devices (PCADs) have emerged as attractive adjuncts in a population of patients with increasing co-morbidities and complexity of coronary artery disease. Indeed, although the role of such devices may have been controversial in the earlier decades, there is emerging consensus that the approach to these patients must be tailored within a framework in which the risk of catastrophic hemodynamic compromise is minimized .
The development of PCADs is progressing at an extraordinary pace and proponents of this technology anticipate that these devices may revolutionize the therapeutic strategies that will be adopted in high-risk patients undergoing PCI. However, a number of questions must be addressed before the interventional community universally adopts such devices. Firstly, although features such as depressed LV function, previous coronary artery bypass surgery, unprotected left main intervention, three-vessel coronary artery disease, last remaining coronary conduit, and age >70 years have traditionally been considered as “high risk,” there is currently no universal definition of “high risk” and this has been reflected in different studies using different criterion to classify their patients as high risk. Secondly, although PCADs may be an attractive adjunct in the setting of high-risk PCI, the operator must ensure that the morbidity and mortality associated with any such device are far outweighed by the benefits that will be derived both peri- and post-procedurally. In this context, and more recently in patients presenting with ST-elevation myocardial infarction (STEMI), the intra-aortic balloon pump (IABP) (MAQUET Cardiovascular, USA), the Impella Recover LP 2.5 (Abiomed-Impella Cardiosystems AG, Germany), and the TandemHeart (Cardiac Assist, Pittsburgh, PA, USA) have emerged as the PCADs of choice in part due to their safety and efficacy and in part due to their relative ease of use within the cardiac catheterization laboratory ( Table 1 ).
| Author | Number of patients | Primary/main end point | P Value/conclusion |
|---|---|---|---|
| IABP in AMI | |||
| O’Rourke et al. | 30 | Reduction in mortality and infarct size | No benefit with IABP |
| Kono et al. | 45 | Patency of the IRA in patients failing early lytic therapy | 74% vs. 32%; P <.05 |
| Ohman et al. | 182 | Patency of the IRA and MACE | 8% vs. 21%; P <.05 |
| 13% vs. 24%; P <.05 | |||
| Stone et al. | 437 | Composite of death, MI, IRA occlusion, stroke, heart failure, and sustained hypotension | 28.9% vs. 29.2%; P =1.0 |
| Van’t Hof et al. | 238 | Composite of death, MI, stroke, and ejection fraction <30% | 26% vs. 26%; P =.94 |
| IABP in high-risk PCI | |||
| Brodie et al. | 1,490 | MACE | Trend favoring IABP |
| Briguori et al. | 133 | MACCE | 0% vs. 17%; P =.001 |
| Mishra et al. | 115 | MACE | 12% vs. 32%; P =.32 |
| Perera et al. | 301 | MACCE | 14.6% vs. 15.3%; P =.35 |
| Impella in AMI | |||
| Sjauw et al. | 20 | Safety and feasibility | Improved hemodynamics |
| Lam et al. | 6 | Safety and feasibility | Improved hemodynamics |
| Impella in high-risk PCI | |||
| Dixon et al. | 20 | MACE and structural complications | 20% MACE |
| Sjauw et al. | 144 | MACCE | 12% MACCE |
| Henriques et al. | 19 | Safety and feasibility | No complications |
| TandemHeart | |||
| Vranckx et al. | 23 | Safety and feasibility | Improved hemodynamics |
| Gimelli et al. | 11 | Safety and feasibility | No MACE |
| Kar et al. | 5 | Safety and feasibility | No complications |
| Al-Husami et al. | 6 | Safety and feasibility | No complications |
| Aragon et al. | 8 | Safety and feasibility | No complications |
2
Intra-aortic balloon pump
The IABP is an over-the-wire balloon catheter that is inserted through a 7.5F sheath. The catheter has a fiberoptic sensor that allows not only timing accuracy but also beat-to-beat adjustments depending upon the hemodynamic requirements of the patient. The hemodynamic effects of the IABP include decreases in the LV end-diastolic pressure, mean left atrial pressure, pulmonary artery pressure, right atrial pressure, afterload, myocardial oxygen consumption, and an increase in the coronary perfusion pressure .
Since its first clinical use by Kantrowitz et al. in patients with cardiogenic shock, the use of IABP has expanded to provide circulatory support in patients with decompensated heart failure, postoperative LV dysfunction, STEMI, and high-risk PCI. Given its ease of implantation, low cost, and low complication rate, the IABP remains the most commonly used PCAD with an estimated 30% use in patients undergoing complex procedures in the United States .
2.1
IABP in acute MI
In one of the earliest studies to assess the role of the IABP in patients with acute MI, O’Rourke et al. randomized 30 patients with early transmural MI complicated by acute heart failure to either IABP therapy ( n =14) or standard medical therapy ( n =16). IABP was commenced at a mean of 7.1 h after the onset of pain and remained in situ for an average period of 4.5 days. This study failed to show any beneficial effects of IABP on morbidity, mortality, or modification in infarct size.
Kono et al. subsequently examined the effects of diastolic augmentation with an IABP to improve the late patency of the infarct-related coronary artery post thrombolysis in 45 patients in whom thrombolysis with tissue-type plasminogen activator had failed to establish Thrombolysis In Myocardial Infarction (TIMI)-3 flow. Compared to conservative therapy, IABP was associated with significantly higher rates of TIMI-3 flow (74% vs. 32%; P <.05), lower residual percent stenosis (42±5% vs. 68±6%; P <.01), and larger minimal lumen diameter (1.6±0.1 vs. 0.9±0.2; P <.01) in the infarct-related artery. This study therefore supported the use of IABP in patients who had failed lytic therapy.
Ohman et al. further evaluated the safety and efficacy of the IABP in 182 patients undergoing emergency coronary angioplasty within the first 24 h of an acute MI. In this setting, IABP was associated with significantly lower rates of re-occlusion of the infarct-related artery (8% vs. 21%; P <.05) and the composite clinical end point of death, stroke, re-infarction, need for emergency revascularization, or recurrent ischemia (13% vs. 24%; P <.05). The rates of vascular or bleeding complications were similar in the two groups [5% vs. 2% ( P >.05) and 2% vs. 1% ( P >.05), respectively]. This study further supported the use of IABP in the setting of acute MI.
The beneficial effects of the IABP in the setting of acute MI were not replicated in either the PAMI-II (Behalf of the Second Primary Angioplasty In Myocardial Infarction) trial or the study by Van’t Hof et al. . PAMI-II undertook cardiac catheterization in 1100 patients presenting within 12 h of an acute MI and then categorized patients undergoing primary angioplasty, on the basis of clinical and angiographic variables, into high risk ( n =211) and low risk ( n =226) . High risk was defined as age >70 years, three-vessel coronary artery disease, left ventricular ejection fraction (LVEF) ≤45%, vein graft occlusion, malignant ventricular arrhythmia, and suboptimal angioplasty result. This group received 36–48 h of IABP counterpulsation, while the low-risk group was treated in the conventional fashion. This trial demonstrated no benefit of IABP with regard to the primary combined end point of death, re-infarction, infarct-related artery occlusion, stroke, or new-onset heart failure or sustained hypotension (28.9% vs. 29.2%; P =.95). Although the IABP cohort had a modest reduction in recurrent ischemia (13.3% vs. 19.6%; P =.08) and subsequent unscheduled repeat catheterization (7.6% vs. 13.3%; P =.05), there were no differences in the rates of infarct-related artery re-occlusion (6.7% vs. 5.5%; P =.64), re-infarction (6.2% vs. 8.0%; P =.46), or mortality (4.3% vs. 3.1%; P =.52). Furthermore, IABP was associated with an increased risk of stroke (2.4% vs. 0%; P =.03).
The efficacy of adjunctive IABP therapy in patients undergoing primary angioplasty was further examined by Van’t Hof et al. . A total of 238 patients presenting within 3 h of an acute MI undergoing primary angioplasty were randomized to either concomitant IABP therapy for 48 h ( n =118) or conventional therapy ( n =120). The other inclusion criterion was age <70 years, anterior, or nonanterior infarct location with cumulative ST-segment deviation of more than 20 mm. IABP did not lead to a significant change in the primary end point of the combination of death, recurrent myocardial infarction, stroke, or LVEF <30% at 6 months (26% vs. 26%; P =.94). The secondary end points of enzymatic infarct size, LVEF, and “weighted unsatisfactory outcome score” were also similar in both groups.
A subsequent meta-analysis of the randomized trials of IABP therapy in high-risk STEMI patients has also failed to demonstrate any benefit of IABP in the 30-day mortality (risk difference, 1%; 95% confidence interval, −3.0% to 4.0%; P =.75) or changes in LVEF (mean difference, −0.1%; 95% confidence interval, −2.2% to 2.0%; P =.93). However, the IABP was shown to be associated with increased rates of bleeding (6%; 95% confidence interval, 1.0–11%; P =.02) and stroke (2%; 95% confidence interval, 0–4%; P =.03) . It therefore appears that, on the basis of current evidence, the routine prophylactic use of an IABP in patients with acute MI without hemodynamic instability cannot be supported.
2.2
IABP in elective high-risk PCI
In contrast to the use of IABP in the setting of acute MI, there is limited data regarding its potential benefits in elective high-risk PCI. In a registry of 1490 consecutive patients with acute MI undergoing primary angioplasty, Brodie et al. showed that the use of IABP prior to intervention was a significant predictor of freedom from major adverse cardiac events (MACE). Although this beneficial effect was most pronounced in patients with cardiogenic shock, a clear trend toward fewer events with prophylactic IABP was also noted in those with congestive heart failure or low LVEF.
One of the earliest randomized studies to address this issue was performed by Briguori et al. who randomized 133 consecutive high-risk patients undergoing elective PCI to either prophylactic IABP insertion ( n =61) or conventional PCI ( n =72). High risk was defined as an LVEF ≤30% and at least one of the following: jeopardy score ≥8, ongoing ischemia, severe disease in a vessel giving collaterals to a totally occluded second vessel supplying at least 40% of the LV myocardium, and left main equivalent disease. The IABP was associated with a significant reduction in the rate of intraprocedural major adverse cardiac and cerebral events (MACCE) (defined as MI, severe hypotension and/or shock, urgent CABG, stroke, and death) (0% vs. 17%; P =.001). Using stepwise logistic regression, the group identified elective IABP support, jeopardy score, and female sex as correlates of intraprocedural events. This study therefore supported the concept of prophylactic IABP insertion in high-risk elective PCI.
The beneficial effects of prophylactic IABP in this setting were further supported by Mishra et al. who compared the outcome of high-risk patients undergoing elective PCI and who either had a prophylactic IABP ( n =69) or an emergency IABP ( n =46) because of an intraprocedural complication. High-risk patients were defined as those having ≥1 of the following: acute coronary syndrome with stable hemodynamics, congestive cardiac failure, LVEF ≤30%, multivessel disease, left main intervention, PCI of ≥1 saphenous vein graft, and pulmonary capillary wedge pressure (PCWP) ≥15. Patients with cardiogenic shock, STEMI, or ventilated patients were excluded. In this study, the prophylactic insertion of an IABP was associated with a reduction in in-hospital mortality (0% vs. 22%; P <.01) as well as in mortality (8% vs. 29%; P <.01) and MACE (12% vs. 32%; P =.02) at 6 months. The incidence of vascular complications was similar except for major bleeding which was more common in the prophylactic group (15% vs. 3%; P =.03).
The landmark randomized trial addressing the efficacy of elective IABP insertion before elective high-risk PCI has been the BCIS (Balloon pump-assisted Coronary Intervention Study)-1 trial . The study randomized 301 high-risk patients, defined as LVEF <30% and one of BCIS-1 myocardial jeopardy score ≥8, left main stenosis, or a target vessel that provided collaterals supplying an occluded vessel that supplies >40% of myocardium, to either prophylactic IABP prior to PCI ( n =151) or conventional PCI ( n =150). The results, presented at TCT 2009, showed that the elective use of IABP in this population did not alter either the primary end point of MACCE (14.6% vs. 15.3%; P =.35) or the major secondary end point of 6-month mortality (4.6% vs. 7.3%; P =.32). Although major bleeding was similar in the two groups (3.3% vs. 4%; P =.77), the incidence of minor bleeding was greater in the IABP group (15.9% vs. 7.3%; P =.02).
Although at first glance it appears that the IABP may have no application as an adjunct in the management of high-risk patients undergoing PCI, it is tempting to speculate that, in patients with severely depressed LV function and a very high jeopardy score, the IABP may at least have favorable intraprocedural effects and minimize the risk of hemodynamic collapse.
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