Background
The five-stage Society for Cardiovascular Angiography and Intervention (SCAI) cardiogenic shock classification scheme can stratify hospital mortality risk in patients admitted to the cardiac intensive care unit (CICU). We sought to evaluate the SCAI shock classification for prediction of post-discharge mortality in CICU survivors.
Methods
We retrospectively analyzed hospital survivors admitted to a single CICU between 2007 and 2015. SCAI CS stages A through E were classified using CICU admission data using a previously published algorithm. All-cause post-discharge mortality was compared across SCAI stages using Kaplan-Meier analysis and Cox proportional hazards models.
Results
Among 9096 unique hospital survivors, 43.2% had acute coronary syndrome (ACS), 44.6% had heart failure (HF), and 8.7% had cardiac arrest (CA) on admission. The proportion of patients in each SCAI shock stage was: A, 49.1%; B, 30.6%; C, 15.2; D/E 5.2%. Kaplan-Meier survival at 5 years in each SCAI shock stage was: A, 88.2%; B, 81.6%; C, 76.7%; D/E, 71.7% ( P < .001 by log-rank). Each higher SCAI shock stage was associated with increased adjusted post-discharge mortality compared to SCAI shock stage A (all P < .001); results were consistent among patients with ACS or HF. Late hemodynamic deterioration after 24 hours, but not an admission diagnosis of CA, was associated with higher post-discharge mortality.
Conclusions
The SCAI shock classification assessed at the time of CICU admission was predictive of post-discharge mortality risk among hospital survivors, although an admission diagnosis of CA was not. The SCAI shock classification can be used for post-discharge mortality risk stratification.
Cardiogenic shock (CS) is a complex and frequently lethal acute cardiovascular disease with contemporary short-term mortality rates remaining 35% to 40%. Patients with acute myocardial infarction (MI) complicated by CS who survive to hospital discharge appear to have an elevated risk of subsequent mortality compared to patients with MI alone, although studies reporting the effects of CS on long-term outcomes are conflicting. Few published studies have focused specifically on predictors of post-discharge mortality among CS patients who survive to hospital discharge. The majority of studies investigating post-discharge outcomes among patients with CS have examined limited populations, such as Medicare patients ≥65 years or acute MI patients. It remains uncertain whether the initial severity of CS itself influences post-discharge outcomes among hospital survivors. If shock severity was a determinant of post-discharge mortality, this could explain the divergent findings in prior studies comparing long-term mortality in MI patients with and without CS. Patients with concomitant cardiac arrest (CA) in the setting of MI or CS have a substantially increased risk of short-term mortality, yet the presence of CA may not increase post-discharge mortality among hospital survivors with MI.
Recognizing the heterogeneity of CS patient populations, the Society for Cardiovascular Angiography and Intervention (SCAI) recently released an expert consensus statement proposing a novel CS classification scheme, which categorizes patients with or at risk of CS into worsening stages of hemodynamic compromise for the purposes of facilitating patient care and research. The SCAI CS classification consensus statement describes five stages of CS, each of which may have an “A” modifier signifying the occurrence of cardiac arrest (CA). We recently reported that a simplified SCAI shock stages classification algorithm could effectively stratify hospital mortality risk among unselected CICU patients using data from the first 24 hours of CICU admission, in a manner amplified by the presence of CA. Given the lack of prognostic tools for predicting post-discharge outcomes among CS patients, we sought to determine whether the SCAI shock stages classification could also stratify post-hospital outcomes using data from the first 24 hours of the CICU admission.
Methods
Study population
This study was approved by the Institutional Review Board of Mayo Clinic (IRB # 16-000722) as posing minimal risk to patients, and was performed under a waiver of informed consent. We retrospectively analyzed hospital survivors from a database of consecutive unique adult patients aged ≥18 years admitted to the CICU at Mayo Clinic Hospital St. Mary’s Campus between January 1, 2007 and December 31, 2015; patients who died in the hospital were excluded from the primary analysis. The Mayo Clinic CICU is a closed 16-bed unit serving critically ill cardiac medical patients. Postoperative cardiac surgery patients and patients receiving extracorporeal membrane oxygenation (ECMO) support are cared for in a separate cardiovascular surgical intensive care unit and were not included in this study. In order to minimize the risk of survival and treatment biases associated with CICU readmissions, only data from each patient’s index CICU admission were analyzed. According to Minnesota state law statute 144.295, patients may decline authorization for inclusion in observational research studies and such patients were excluded from the study.
Data sources
We recorded demographic, vital sign, laboratory, clinical and outcome data, as well as procedures and therapies performed during the CICU and hospital stay; invasive hemodynamic data, physical examination, symptoms, imaging and ECG data were not available. All relevant data were extracted electronically from the medical record using the Multidisciplinary Epidemiology and Translational Research in Intensive Care Data Mart, a repository storing clinical data from all intensive care unit admissions at the Mayo Clinic Rochester. The admission value of all vital signs, clinical measurements and laboratory values was defined as either the first value recorded after CICU admission or the value recorded closest to CICU admission. In addition, vital signs were recorded every 15 minutes during the first hour after CICU admission. The shock index was defined as the ratio of heart rate to systolic blood pressure. Admission diagnoses were defined as all International Classification of Diseases ( ICD )- 9 diagnostic codes on the day of CICU admission and one day before or after, including acute coronary syndrome (ACS, including all subtypes), heart failure (HF), CA, shock, CS, ventricular tachycardia/ventricular fibrillation (VT/VF), supraventricular tachycardia/atrial fibrillation (SVT/AF), respiratory failure and sepsis.
The APACHE-III score, APACHE-IV predicted hospital mortality and Sequential Organ Failure Assessment (SOFA) score were automatically calculated for all patients using data from the first 24 hours of CICU admission using previously-validated electronic algorithms, with missing variables imputed as normal as the default. The Charlson Comorbidity Index (CCI) and individual comorbidities were extracted from the medical record using a previously validated electronic algorithm. Severe acute kidney injury (AKI) during the CICU stay was defined as KDIGO stage 2 or 3 AKI based on serum creatinine: doubling of serum creatinine from baseline, increase in serum creatinine to ≥4.0 mg/dl or new dialysis initiation; baseline creatinine was defined as either most recent pre-admission creatinine within 1 year or admission creatinine (whichever was lower), and patients with a prior history of dialysis were not considered in this AKI analysis.
Definition of shock stages
We defined hypotension/tachycardia, hypoperfusion, deterioration and refractory shock using data from CICU admission through the first 24 hours in the CICU, as previously described (Supplemental Table 1 ). We mapped the five SCAI shock stages with increasing severity (A through E) using combinations of these variables at presentation (Supplemental Table 2) . Due to the low number of hospital survivors with SCAI shock stage E, patients with SCAI shock stages D and E were combined for this analysis (SCAI shock stage D/E). Late deterioration was defined as an increasing number or dose of vasopressors after 24 hours, and was considered independently of their initial SCAI shock stage.
Statistical analysis
The primary endpoint was all-cause post-discharge mortality up to 5 years; secondary endpoints included CICU and hospital length of stay (LOS), discharge disposition and all-cause rehospitalization within 1 year. The time of hospital discharge was the starting point for follow-up, including for patients not discharged to home. Mortality and other outcome data were extracted from Mayo Clinic electronic databases, the state of Minnesota electronic death certificates and the Rochester Epidemiology Project database. Categorical variables are reported as number (percentage) and the Pearson chi-squared test was used to compare groups. Continuous variables are reported as mean (±standard deviation) and the Wilcoxon rank-sum test was used to compare groups. Post-discharge survival between groups was compared using Kaplan-Meier survival analysis, with groups compared using the log-rank test. Cox proportional hazards models were used to determine the association between SCAI shock stages and 5-year all-cause post-discharge mortality before and after adjusting for age, gender, race, CCI, late deterioration, admission diagnosis of CA, and inpatient coronary angiography and PCI. Two-tailed P < .05 were considered statistically significant. Statistical analyses were performed using JMP Pro version 14.1.0 (SAS Institute, Cary, NC).
Results
Study population
We screened 12,904 adult admissions to the CICU during the study period and excluded 2900 admissions (1877 readmissions, 755 without Minnesota Research Authorization and 268 whose admission did not occur entirely within the study period), yielding 10,004 unique patients in the database ( Supplemental Figure 1 ). A total of 908 (9.1%) patients died in the hospital, leaving 9096 hospital survivors for inclusion in the primary analysis. Hospital survivors differed substantially from inpatient deaths ( Supplemental Table 3 ), including a lower age, fewer comorbidities, lesser severity of illness, a lower prevalence of critical care diagnoses and less frequent requirement for critical care therapies. The distribution of SCAI shock stages differed between hospital survivors and inpatient deaths ( P < .001; Supplemental Figure 1 ).
The mean age of hospital survivors was 67.0 ± 15.3 years, including 3380 (37.2%) females. An admission diagnosis of ACS was present in 43.2%, HF in 44.6%, and CA in 8.7%. SCAI stage in hospital survivors was: A, 49.1%; B, 30.6%; C, 15.2; D/E 5.2% ( Supplemental Figure 1 ). Baseline characteristics in hospital survivors stratified by SCAI shock stage are shown in Table I . Significant trends were observed across SCAI shock stages in several baseline characteristics, including higher illness severity, more critical care admission diagnoses and greater use of CICU therapies and procedures with increasing SCAI shock stage.
| Variable | % with available data | SCAI stage A (n = 4463) | SCAI stage B (n = 2786) | SCAI stage C (n = 1379) | SCAI stage D/E (n = 468) | P |
|---|---|---|---|---|---|---|
| Baseline demographics | ||||||
| Age | 100% | 66.9 ± 14.7 | 65.8 ± 15.8 | 69.5 ± 16.1 | 67.3 ± 14.2 | <.001 |
| Female gender | 100% | 1511 (33.9%) | 1125 (40.4%) | 565 (41.0%) | 179 (38.2%) | <.001 |
| White race | 100% | 4166 (93.4%) | 2578 (92.5%) | 1250 (90.6%) | 418 (89.3%) | <.001 |
| CICU LOS | 100% | 2.1 ± 4.3 | 2.5 ± 5.4 | 2.4 ± 2.3 | 5.2 ± 6.0 | <.001 |
| Hospital LOS | 100% | 6.4 ± 12.6 | 8.5 ± 11.0 | 8.0 ± 10.0 | 16.4 ± 18.9 | <.001 |
| Comorbidities | ||||||
| CCI | 99.7% | 2.0 ± 2.5 | 2.4 ± 2.6 | 2.7 ± 2.8 | 2.8 ± 2.7 | <.001 |
| Prior MI | 99.7% | 888 (20.0%) | 529 (19.0%) | 262 (19.1%) | 103 (22.1%) | .97 |
| Prior heart failure | 99.7% | 705 (15.8%) | 591 (21.3%) | 280 (20.4%) | 134 (28.7%) | <.001 |
| Prior stroke | 99.7% | 482 (10.8%) | 346 (12.5%) | 198 (14.4%) | 50 (10.7%) | .01 |
| Prior diabetes mellitus | 99.7% | 1186 (26.6%) | 776 (27.9%) | 422 (30.7%) | 150 (32.1%) | <.001 |
| Prior lung disease | 99.7% | 740 (16.6%) | 597 (21.5%) | 299 (21.7%) | 85 (18.2%) | <.001 |
| Prior cancer | 99.7% | 815 (18.3%) | 623 (22.4%) | 335 (24.4%) | 109 (23.3%) | <.001 |
| Prior CKD | 99.7% | 733 (16.5%) | 544 (19.6%) | 356 (25.9%) | 141 (30.2%) | <.001 |
| Prior dialysis | 100% | 121 (2.7%) | 109 (3.9%) | 167 (12.1%) | 67 (14.3%) | <.001 |
| Admission diagnoses | ||||||
| Cardiogenic shock | 98.9% | 142 (3.2%) | 276 (10.0%) | 78 (5.7%) | 211 (45.8%) | <.001 |
| Cardiac arrest | 98.9% | 284 (6.4%) | 229 (8.3%) | 132 (9.7%) | 140 (30.4%) | <.001 |
| VT/VF | 98.9% | 635 (14.4%) | 465 (16.8%) | 214 (15.7%) | 103 (22.3%) | <.001 |
| AF/SVT | 98.9% | 1125 (25.5%) | 1060 (38.4%) | 491 (36.1%) | 199 (43.2%) | <.001 |
| Heart failure | 98.9% | 1598 (36.2%) | 1425 (51.6%) | 647 (47.5%) | 345 (74.8%) | <.001 |
| ACS | 98.9% | 2049 (46.5%) | 1086 (39.3%) | 565 (41.5%) | 185 (40.1%) | <.001 |
| Neither ACS nor HF | 98.9% | 1311 (29.7%) | 26.9%) | 412 (30.3%) | 61 (13.2%) | <.001 |
| Sepsis | 98.9% | 79 (1.8%) | 171 (6.2%) | 75 (5.5%) | 103 (22.3%) | <.001 |
| Respiratory failure | 98.9% | 443 (10.0%) | 540 (19.6%) | 286 (21.0%) | 276 (59.9%) | <.001 |
| Severity of illness | ||||||
| APACHE-III score | 100% | 50.8 ± 17.8 | 59.7 ± 19.7 | 66.2 ± 22.1 | 89.4 ± 27.2 | <.001 |
| APACHE-IV mortality | 100% | 0.094 ± 0.109 | 0.147 ± 0.156 | 0.190 ± 0.179 | 0.418 ± 0.270 | <.001 |
| Day 1 SOFA score | 99.9% | 2.2 ± 1.9 | 3.3 ± 2.6 | 4.1 ± 2.7 | 8.4 ± 3.6 | <.001 |
| Severe AKI in CICU | 90.3% | 227 (5.5%) | 287 (11.3%) | 193 (16.7%) | 190 (48.1%) | <.001 |
| Late deterioration | 100% | 155 (3.5%) | 148 (5.3%) | 67 (4.9%) | 116 (24.8%) | <.001 |
| Therapies and procedures | ||||||
| Invasive ventilator | 100% | 267 (6.0%) | 398 (14.3%) | 186 (13.5%) | 274 (55.6%) | <.001 |
| Noninvasive ventilator | 100% | 493 (11.0%) | 425 (15.2%) | 219 (15.9%) | 149 (31.8%) | <.001 |
| Vasoactive drugs | 100% | 581 (13.0%) | 734 (26.4%) | 118 (8.6%) | 435 (93.0%) | <.001 |
| >1 vasoactive drug | 100% | 189 (4.2%) | 296 (10.6%) | 27 (2.0%) | 250 (53.4%) | <.001 |
| Vasopressors | 100% | 407 (9.1%) | 612 (22.0%) | 101 (7.3%) | 392 (83.8%) | <.001 |
| Inotropes | 100% | 279 (6.2%) | 285 (10.2%) | 27 (2.0%) | 155 (33.1%) | <.001 |
| IABP | 100% | 248 (5.6%) | 300 (10.8%) | 57 (4.1%) | 122 (26.1%) | <.001 |
| PAC | 100% | 227 (5.1%) | 219 (7.9%) | 42 (3.0%) | 122 (26.1%) | <.001 |
| Dialysis | 100% | 100 (2.2%) | 104 (3.7%) | 51 (3.7%) | 80 (17.1%) | <.001 |
| Coronary angiogram | 100% | 2628 (58.9%) | 1387 (49.8%) | 661 (47.9%) | 246 (52.6%) | <.001 |
| PCI | 100% | 1807 (40.5%) | 890 (32.0%) | 401 (29.1%) | 137 (29.3%) | <.001 |
| RBC transfusion | 100% | 277 (6.2%) | 365 (13.1%) | 168 (12.2%) | 154 (32.9%) | <.001 |
| Admission vital signs | ||||||
| Systolic BP | 99.5% | 130.9 ± 22.9 | 115.0 ± 25.9 | 124.1 ± 27.2 | 113.4 ± 28.0 | <.001 |
| Diastolic BP | 96.5% | 72.2 ± 14.5 | 67.4 ± 18.5 | 69.3 ± 17.5 | 65.9 ± 18.8 | <.001 |
| Mean BP | 96.5% | 87.3 ± 15.1 | 79.9 ± 19.4 | 83.7 ± 18.5 | 80.2 ± 20.2 | <.001 |
| Heart rate | 99.5% | 72.3 ± 13.9 | 93.2 ± 27.1 | 84.1 ± 25.5 | 88.3 ± 25.1 | <.001 |
| Shock index | 99.5% | 0.57 ± 0.15 | 0.83 ± 0.29 | 0.71 ± 0.28 | 0.82 ± 0.31 | <.001 |
| Respiratory rate | 96.2% | 17.3 ± 5.2 | 19.0 ± 5.9 | 19.0 ± 5.8 | 20.0 ± 6.0 | <.001 |
| Oxygen saturation | 99.5% | 96.6 ± 4.1 | 95.8 ± 5.1 | 95.7 ± 6.4 | 93.6 ± 7.7 | <.001 |
| Glasgow Coma Scale | 98.0% | 14.6 ± 1.8 | 14.0 ± 2.7 | 13.9 ± 2.9 | 10.6 ± 4.9 | <.001 |
| Admission laboratories | ||||||
| BUN | 96.4% | 23.2 ± 16.1 | 26.3 ± 18.3 | 28.6 ± 19.0 | 33.8 ± 21.0 | <.001 |
| Creatinine | 96.6% | 1.16 ± 0.78 | 1.29 ± 1.03 | 1.73 ± 1.72 | 1.81 ± 1.36 | <.001 |
| Bicarbonate | 96.9% | 24.6 ± 3.6 | 24.0 ± 4.2 | 23.5 ± 4.3 | 21.5 ± 5.5 | <.001 |
| Anion gap | 90.9% | 11.0 ± 2.9 | 11.4 ± 3.1 | 12.4 ± 3.7 | 14.0 ± 4.3 | <.001 |
| Lactate | 17.6% | 1.2 ± 0.4 | 1.3 ± 0.4 | 2.7 ± 1.9 | 3.5 ± 2.6 | <.001 |
| Arterial pH | 27.6% | 7.39 ± 0.08 | 7.37 ± 0.08 | 7.37 ± 0.09 | 7.33 ± 0.10 | <.001 |
| Arterial base deficit | 30.2% | −0.5 ± 4.9 | 0.5 ± 5.0 | 2.0 ± 5.0 | 4.3 ± 5.5 | <.001 |
| Hemoglobin | 96.7% | 12.5 ± 2.0 | 11.9 ± 2.2 | 11.9 ± 2.3 | 11.8 ± 2.4 | <.001 |
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