In the present study, an algorithm to identify patients that may be at a higher risk of developing future CS was developed. The model can continuously monitor complex patient trajectories in the background. Patients identified as high risk are substantially more likely to develop CS than those in the low-risk cohort. Moreover, high risk patients were identified with lead-time that future studies could use to evaluate if it would alter the course of their treatment and therefore outcomes.
Our method follows in the tradition of identifying risk categories for cardiac patients. Risk prediction models from the Acute Decompensated Heart Failure Registry[19], Get with the Guidelines-Heart Failure[20], and other similar retrospective data[6, 21, 22] predict the risk of in-hospital and out-of-hospital mortality at the time of admission. Since these models do not track the dynamic variables of a hospitalized patient with ADHF but rather provide a single snapshot, they are challenging to use to change management or outcomes. Additionally, they are not automated but require clinicians to calculate a score, which increases work burden. Some of these issues are overcome by early warning systems (EWS)[23, 24] such as the modified EWS, Targeted Real-time EWS (TREWS)[24], which can provide continuous monitoring for adverse outcomes such as cardiac arrest, ICU admission or mortality. Unfortunately, these systems have had variable performance, and alert in close proximity to the outcome event which may not be sufficient to change the trajectory of a patient’s clinical outcome[24].
We also demonstrate that age, systolic blood pressure, heart rate, temperature, blood urea nitrogen, sodium, oxygen saturation, venous pH, hemoglobin, hydralazine use, trend of respiratory rate and trend of systolic blood pressure are each individually associated with increased risk of developing CS in our model. These predictive variables cannot be directly compared with previous risk prediction models as those typically used single time point measurements at admission and evaluated inpatient or post-hospitalization mortality[19–22, 6]. Whereas certain variables such as hemoglobin, sodium and systolic blood pressure have previously been associated with adverse outcomes in ADHF, to our knowledge this is first time that temperature and trends of vital signs have been shown to be associated with risk of developing CS. In our study, individuals who develop CS are more likely to have a lower temperature which may be related to the peripheral vasoconstriction seen in a low output state. Just as importantly, we also demonstrate that most trends (such as heart rate) are not as pertinent for risk prediction.
How does our work translate?
Unlike previous approaches, our method focuses specifically on identifying patients at high risk for CS by continuously monitoring their EHRs over the course of their stay. This method is one of a new generation of technologies that seek to take advantage of the tremendous stores of information in EHRs by combining the strengths of computers and clinicians. Computers have unlimited attention, and can monitor vast quantities of data without tiring, while clinicians have the wisdom to act appropriately when important information is made available to them. We find that a patient characterized as high-risk has a greater than 10 times the odds of developing CS.
Although, this model at a threshold of 0.1 had a positive predictive value of 5%, which at first glance would be concerningly low. However, it is not unusual for certain risk prediction tools to have low positive predictive value[25], for example the CHA2DS2-VASc score for atrial fibrillation has been used with a risk score of 2 as significant, which equates to an estimated annual stroke risk of 2.2% per year[26]. Similarly, any risk prediction model for CS is not designed to be used in isolation but provide clinicians an aid in addition to their clinical evaluation.
We do not believe a model like ours would be implemented as a best practice alert. Instead, we see the future of medicine involving a dashboard for clinicians where algorithms monitor patients for risk stratification for poor outcomes during continuous surveillance. This dashboard would act to aid the clinician during their daily decision making for patients.
To that extent, we ensured that our model could provide timely, automated method of entrance for likely ADHF by using intravenous diuretics as a surrogate to diagnose ADHF. Although this is a very sensitive approach, the specificity for ADHF is reduced and therefore reduces the positive predictive value for CS, e.g., if diuretics are administered incorrectly or for other diagnoses such as renal or hepatic disease. However, we believe that in addition to a clinician evaluation, particularly when the trajectory of a patient is unclear, a risk stratification by an algorithm could aid a clinician to vary their level of concern for CS. For example, does a rise in creatinine suggest overdiuresis or low-output state. In such cases, the risk-cohort classification of a patient may prompt the clinical team to seek a cardiology consult, or otherwise alter patient care.
We do believe that our model requires continual improvement and further development. For example, future work by ourselves and other groups could include other variables such as echocardiogram data or other imaging tools, ordering of certain tests etc. could help improve the model further. In addition, a suite of algorithms in a clinician dashboard for presentations such as shortness of breath may evaluate for patients at risk of respiratory failure requiring intubation, renal failure requiring renal replacement therapy, and cardiac failure at risk of CS. These approaches will require collaboration between computer science and clinical teams to help us reach the goal of precision medicine leveraging big data and greater computing skills available in the 21st century.
Risk prediction tools are common in the scientific literature, but few are regularly used and implemented into daily practice[27]. Early risk prediction tools are even more relevant as providers spend increasing amounts of time on administrative and documentation activities with frequent interruptions to patient care, and experience increasing volumes of patient data[28, 29]. As our study shows, the overall inpatient mortality for ADHF is low (4% in our study) unless the patient deteriorates into CS, which increased the mortality by more than 8-fold, demonstrating the need to improve care for these patients.
Although mortality after CS has remained stagnant[1, 2, 4, 5, 3, 6], recent evidence in CS after acute myocardial infarction demonstrates that early, coordinated, aggressive treatment improves inpatient mortality[9]. We believe that similar early, tailored treatment in patients identified to have a high-risk of developing CS may improve outcomes. Using the expert consensus from The Society of Cardiovascular Angiography and Interventions, our algorithm attempts to identify patients in Stage B or early in Stage C of shock in comparison to later stages where outcomes are worse[10]. As recently demonstrated, the later the stage of CS the significantly higher the mortality[10, 30]. To that extent, we demonstrate a model with an AUC of 0.77 where positive cases are identified at a median 1.7 days before the diagnosis of CS was made by the clinical team. This early identification of high-risk patients would provide clinicians time to initiate individualized, tailored treatment strategies to proactively prevent further decompensation instead of reactively responding after CS has already developed.
Further, we demonstrate that from the time of high-risk categorization by our model to clinical diagnosis of CS approximately 1/8 patients received therapy that may have worsened their clinical status likely due to lack of recognition of worsening ADHF. In addition, in half of patients there was time and opportunity to undertake early tailored treatment, which may include simple approaches such as discontinuation of negative inotropes or appropriate diuretic adjustments, to more invasive options such as pulmonary artery catheter insertion for hemodynamic guided therapy, or early initiation of inotropes that may reduce length of hospitalization, and mortality. In addition, the patients identified as high-risk while in the emergency department or medicine services may be selectively referred for admission to a cardiology team or referred for an early cardiology consult. Although these treatment options exist, it is unclear if identification of cases ~ 1.7 days earlier would change a patient’s clinical trajectory. What requires further study is to evaluate if such an approach reduces hospital morbidity, mortality and length of stay; as demonstrated in the sepsis literature[31]. Therefore, we propose a new paradigm where clinical acumen is combined with our prediction model to risk stratify patients for individualized, patient-specific treatment (Fig. 3).
Our study has several strengths including the several years of data from three hospitals and the use of novel machine learning tools for risk prediction. Limitations include the moderate number of CS cases that limits the number of variables and learning that is possible. Additionally, we use data from one healthcare system; further studies using data from other systems will be required to improve model generalizability and robustness. As discussed above, several variables are not included such as echocardiogram data as these were not accurately available. Finally, EHR data does have several weaknesses including missing data, non-systematic way of data collection for each patient, and erroneous recording by providers. However, this reflects real-world practice and any model that is to be clinically useful needs to account for these weaknesses[32].
In this study, we present a risk prediction tool that can use continuous EHR data monitoring in patients with ADHF to help identification of patients at a high-risk of CS. Early identification of at-risk patients is essential to allow for enough time to change disease trajectory. CS is a state of not only decompensated cardiac failure but also end-organ dysfunction and is therefore a multi-organ disease. Current approaches in CS have been inadequate in improving outcomes. Future intervention studies are needed using this model to observe how early identification and potential effects on treatment strategies may alter patient outcomes.