Jennifer Cowger, University of Michigan Health System, AnnArbor, USA, and others reported in the Journal of the American College of Cardiology that a new risk score—the HeartMate II Risk Score—could be used for mortality risk stratification in patients with a HeartMate II (Thoratec) left ventricular assist device
Cowger et al commented that the Integrated Registry for Mechanically Assisted Circulatory Support (INTERMACS) and the Destination Therapy Risk Score (DTRS) were most widely used risk scores in patients with a left ventricular assist device (LVAD), but wrote: “Derived in the pulsatile LVAD era, the DTRS was recently shown to provide poor discrimination for bridge to transplantation patients and only modest discrimination for destination therapy patients supported with continuous flow LVADs.” They added that, therefore, “a reassessment and revision of LVAD candidate risk prediction is warranted. The primary objective of this analysis was to develop and validate a risk model for predicting LVAD outcome in the ‘continuous flow era’ of mechanical circulatory support”.
The investigators assessed data from the HeartMate II bridge to transplantation or destination therapy clinical trials (1,122 patients overall) to identify risk factors for increased mortality after LVAD implantation. Patients were randomised into a derivation cohort (583) and a validation cohort (539).
They found that, in a multivariate analysis of the derivation cohort, increased age, renal dysfunction, greater hypoalbuminemia, coagulopathy, and LVAD implantation in less experienced centres were all associated with increased mortality. Therefore, the factors age, serum creatinine, albumin, international normalised ratio (INR), and LVAD implanting centre were then used to create the HeartMate II Risk Score (HMRS) for predicting 90-day mortality. Low risk was a score of <1.58, median risk was a score of ≤2.48, and high risk was a score of >2.48. Within the derivation cohort, 90-day mortality was 4% for patients considered to be low risk according to the new risk score, 16% for moderate risk patients, and 29% for high-risk patients (p>0.001). Cowger et al commented: “Pair-wise comparisons showed that both the high- and moderate-risk groups had significantly worse outcomes than the low-risk groups (p<0.001).” Similar observations were made in the validation cohort.
Additionally, Cowger et al compared the risk score with the DTRS and by device indication. They found that: “The HMRS provided significantly higher risk discrimination than the DTRS when evaluated in the total HeartMate II sample (p<0.001). When evaluated by device intent (bridge to transplantation or destination therapy), the HMRS was also more discriminative than the DTRS (p<0.05).”
According to the authors, the new risk score can be used to provide “additional knowledge of patient risk to help in education and communication with referring cardiologists, patients, families, and the clinical LVAD team.” They added that it could also highlight important goals for preoperative optimisation and “identify a period of optimal patient ‘fitness’ for surgery.” However, they said the risk score was not meant to “supplant or supersede clinical judgement” or be used to determine whether or not a LVAD procedure should be performed.
Cowger told Cardiovascular News: “In this era of new device technology and evolving patient demographics, it is clear the DTRS is no longer valid for risk stratification for bridge to transplantation or destination therapy LVAD support. The HMRS was devised in a cohort of patients supported with continuous flow technology and, unlike the DTRS, included both bridge to transplantation and destination therapy patients in its derivation. The HMRS components are not novel–they have been identified as risk factors for poor outcome in prior risk analyses.However, their coefficients of risk were drawn from a larger sample size which will hopefully make the model more discriminative. Assessment of calibration with validation studies is imperative. Until then, we do not know how precise the HMRS LVAD mortality risk estimates are.”