| Summary: | Introduction: Reversible myocardial depression (RMD) is a transient impairment of left ventricular systolic function. This has been described in sub populations of patients experiencing critical illness, but it is unclear if the epidemiological features are generalisable to the broader populations of critically ill adults. Previous work has identified that RMD is not benign and has been associated with a range of adverse sequelae such as arrhythmia, left ventricular outflow tract obstruction, and intra-ventricular thrombus. Consequently, studies were designed to determine the incidence, time course, and associated risk factors for the development of myocardial depression in the general population of adults experiencing critical illness. Methods: Myocardial depression was defined as a decrease in left ventricular ejection fraction =5% from AICU baseline and was assessed using serial transthoracic echocardiography. Three studies were conducted - two prospective observational cohort studies and a retrospective analysis. The incidence, absolute decrease in ejection fraction, and time course of myocardial depression was described. Routinely available demographic and clinical variables were collected. These were then rationalised and trialled as candidate explanatory variables in a logistic regression model to predict the development of myocardial depression. Results: The incidence of myocardial depression was between 16.3 - 34%, which occurred around day four of AICU admission. The median decline in LVEF at the onset of myocardial depression was between 6.5 - 14.7%, which progressed to between 10 - 17.5% at the nadir. Myocardial depression was not entirely reversible, with between 43.7 - 71.4% of participants demonstrating some degree of recovery, with LVEF improving between 13.3 - 20.2% across the studies. The probability of development of myocardial depression can be determined using five routinely collected variables, expressed as a factor; heart rate, systolic blood pressure, the presence of severe sepsis, cardiovascular organ dysfunction and sinus rhythm. Increasing systolic blood pressure, the presence of severe sepsis, and cardiovascular organ dysfunction were associated with increased risk. Increasing heart rate and the presence of sinus rhythm were associated with decreased risk. Model diagnostics indicated that the model was a good fit of the data. The model had a modest discriminating ability, with the area under the receiver operating characteristic curve = 0.69. Conclusion: The incidence of myocardial depression was between 16.3 - 34% of participants, and usually developed around day four of AICU admission. The decreases in left ventricular ejection fraction were considerable and were not always reversible. Myocardial depression can be predicted using routinely collected haemodynamic and clinical variables that are available within the first 24 hours of AICU admission.
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