The superiority of an ERV over an IMS strategy did not reach statistical significance at 30 days in the SHOCK trial (Figure 2). This was because the 9% absolute difference in 30-day survival seen with ERV was less than the expected 20% benefit predicted at the time of the trial design. However, the potential for nine absolute lives saved per 100 treated appears to support this approach. A larger sample size would be required to formally prove this, and future conduct of randomized trials appears unlikely. This ERV strategy is further supported by long-term follow-up survival data. ERV was clearly superior to IMS at 6 months, with 13 lives saved per 100 patients treated. This beneficial effect was stable at 1 year of follow-up (Figure 2). The increasing survival benefit with ERV between 1 and 6 months is in contradistinction to the parallel lines beyond 30 days for thrombolysis over placebo and the decreasing benefit of primary PTCA over thrombolysis at 6 months in patients with acute MI and no shock.[18,19] It is similar to the divergence in the long-term survival curves for patients with normal coronary flow (TIMI III) and those with abnormal flow (TIMI 0-II) in the GUSTO trial.
Overall survival at 1, 6, and 12 months of follow-up. ERV=emergency revascularization; IMS=initial medical stabilization
Only 15% of hospitals in the United States have the capability to perform PTCA. Consequently, adopting a universal strategy of ERV in the setting of CS is difficult. Our experience in the SHOCK study indicates that benefit with an ERV strategy is greatest for those less than 75 years of age, with 20 lives saved at 6 months per 100 patients treated (Figure 3). On the basis of this evidence, we advocate emergent transfer to tertiary facilities for this younger subset of patients. The recently updated American College of Cardiology/American Heart Association (ACC/AHA) guidelines adopt a similar stance, based on current evidence. When transfer is unfeasible and in those greater than 75 years of age, an IMS approach similar to that in the SHOCK trial should be advocated. In the trial, the IMS strategy, which included thrombolysis (63%), IABP support (86%), and physician-directed delayed revascularization (25%), resulted in lower mortality rates than historical controls. This IMS strategy proved equivalent to an ERV strategy among the elderly and seems to be an acceptable initial strategy. Alternatively, selective use of an ERV strategy in patients over 75 years of age was associated with an excellent outcome in the SHOCK registry.
Survival for patients less than 75 years of age. ERV=emergency revascularization; IMS=initial medical stabilization
The mode of revascularization in the setting of CS is best guided by coronary anatomy, and both PTCA and CABG play pivotal roles. In the SHOCK trial, percutaneous intervention was performed in 55% (n=83/152) of patients in the ERV group. The 77% procedural success with percutaneous intervention in this setting is consistent with that of earlier reports and lower than that reported with primary angioplasty in the setting of all ST elevation MIs.[3,24,25] This is presumably due to a combination of diffuse multivessel disease, large thrombus burden, and coronary hypoperfusion. Furthermore, the no reflow phenomenon may occur more often in CS. Successful percutaneous intervention in this setting is clearly associated with a superior outcome and procedural failure is associated with increased 30-day mortality (38% vs.79%; p=0.003). Overall mortality with percutaneous intervention in this randomized trial was 40% (n=105). This is similar to the 44% cumulative mortality (n=1167) reported in 24 previous trials. The use of coronary stents and platelet glycoprotein IIb/IIIa receptor antagonists has revolutionized percutaneous intervention in the past 5 years. A number of single-center experiences in the setting of shock have been reported.[27,28,29,30] In SHOCK, stent and IIb/IIIa receptor antagonist use increased from 0% in 1993-1994 to 74% and 59% in 1997 and 1998, respectively. No increased survival benefit was apparent in these small subsets of patients.
The feasibility of CABG in the setting of CS has been previously reported. In the SHOCK trial, CABG was recommended for severe triple-vessel coronary artery disease, left main artery disease, and failed percutaneous intervention. Thirty-eight percent (n=57/152) of patients in the ERV group underwent this procedure. Despite more extensive coronary disease, mortality with CABG was similar to that with percutaneous intervention in both the SHOCK trial (41% vs. 40% for patients assigned to ERV or IMS) and registry (28% vs. 46%). The ability to perform complete revascularization and the myocardial protection offered by cardiopulmonary bypass may have contributed to this favorable outcome. CABG appears to be an excellent revascularization option in this scenario.
IABP support was strongly advocated in both arms of the SHOCK trial and played an integral role in the medical stabilization arm. The overall utilization of IABP in this group was 86%, considerably higher than the 24% and 25% balloon pump utilization rates seen with shock in GUSTO-1 and GUSTO-III, respectively. Although conclusions are speculative, IABP may have been largely responsible for the favorable historical outcome seen in this group. This is because there is experimental evidence suggesting enhanced thrombolytic efficacy in this setting. This positive experience is also supported by the large National Registry of Myocardial Infarction (NRMI) database and the randomized, multicenter Thrombolysis and Counterpulsation to Improve Cardiogenic Shock Survival (TACTICS) trial. TACTICS was terminated prematurely because of insufficient patient recruitment, but the results suggest a 9% absolute reduction of mortality at 6 months (p=0.23) with the combination of thrombolysis and IABP. According to these findings, IABP should be used in the management of CS. Unfortunately, IABP use is uncommon in community hospitals. Reasons for this may include lack of physician expertise and cost. Physician education and regional expertise are potential solutions. Results of the SHOCK and TACTICS trials may help to rectify this problem.
CHF. 2003;9(1) © 2003 Le Jacq Communications, Inc.
Cite this: Cardiogenic Shock: A Summary of the Randomized SHOCK Trial - Medscape - Jan 01, 2003.