Introduction
Hyperdynamic left ventricular ejection fraction (HDLVEF) on transthoracic echocardiography (TTE) is a frequent finding in the intensive care unit (ICU). In spite of the growing use of TTE in the critical care setting, limited information exists on the etiology, prevalence, and significance of HDLVEF in the ICU.
Prior studies have suggested increased prevalence of HDLVEF in certain patient populations and disease processes. For instance, female gender and obesity have been associated with a higher prevalence of HDLVEF without any clear mechanism. Furthermore, HDLVEF has not been shown to be associated with aerobic fitness[5], which suggests that HDLVEF may be due to a physiologic or pathophysiologic response rather than cardiovascular conditioning. One study demonstrated that in patients with septic shock, HDLVEF was more common in the subset of patients with concurrent cirrhosis. Some research has suggested that HDLVEF in patients with non-traumatic shock is highly specific, but not sensitive, for sepsis. These studies have provided some insight, but the significance of HDLVEF remains grossly undefined.
There have not been any studies that compared outcomes of patients with HDLVEF to those with normal ejection fraction (EF). Using a large, public, de-identified critical care database, we studied the prevalence, characteristics, and outcomes of patients with HDLVEF in an ICU setting.
Methods
We conducted a longitudinal, single center, retrospective cohort study of adult patients who underwent TTE during an ICU admission at the Beth Israel Deaconess Medical Center between 2001 and 2008. Data was extracted from the Multi-parameter Intelligent Monitoring in Intensive Care II (MIMIC II) database. MIMIC II is freely available in the public domain and contains information from electronic medical records of 32,425 patients admitted to the ICUs at the Beth Israel Deaconess Medical Center between 2001 and 2008. Social security death records provided 28-day mortality information. The creation and use of the MIMIC database for research was approved by the institutional review boards of both Beth Israel Deaconess Medical Center and Massachusetts Institute of Technology (IRB protocol 2001-P-001699/3).
All adult patient records in the database were screened for the purpose of inclusion. Data regarding age, gender, simplified acute physiology score (SAPS) [19], laboratory values, vital signs, Diagnosis-Related Group (DRG) codes, and International Classification of Diseases-Ninth Revision (ICD-9) diagnoses were extracted. Medical co-morbidities were represented by the Elixhauser scores for 30 co-morbidities as calculated from the DRG and ICD-9 codes from the respective hospital admission. The maximum values of common pertinent laboratory results were also extracted, including white blood cell count (WBC), lactate, and creatinine. The SAP score is derived
For patients with multiple ICU stays, the first ICU admission was used. Patients in the database were admitted to a variety of ICUs including medical ICU (MICU), surgical ICU (SICU), cardiac ICU (CCU), and cardiac surgical ICU (CSRU). The study was limited to MICU and SICU patients in order to exclude elective admissions. Patients with at least one TTE were included in the cohort. HDLVEF was defined as EF greater than 70% and normal EF was defined as 55-70%. Those with EF less than 55% were excluded from the analysis as these patients are theoretically less likely to tolerate a physiologic insult, treatment or both.
Inclusion and Exclusion Criteria
Of the 23,467 MICU and SICU admissions, 3,851 had a TTE during that admission. Per TTE reports, EF could not be estimated in 100 patients due to poor windows, body habitus or patient positioning; these patients were excluded. 884 patients with depressed EF were also excluded. The final cohort had 2,867 patients, of which 324 had HDLVEF. The time to TTE varied, but the median was approximately 1 day after arrival to ICU, which was similar between the groups with normal EF and HDLVEF.