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Letter by Mirwais et al Regarding Article, "Lower Rates of Heart Failure and All-Cause Hospitalizations During Pulmonary Artery Pressure-Guided Therapy for Ambulatory Heart Failure".

To the Editor: The use of CardioMEMS pulmonary artery pressure sensor is increasing given the findings of the randomized controlled CardioMEMS Heart Sensor Allows Monitoring of Pressure to Improve Outcomes in NYHA Class III Heart Failure Patients trial and financial pressures to reduce heart failure rehospitalization.1 Shavelle et al2 recently published findings from the CardioMEMS postapproval study entitled “Lower Rates of Heart Failure and All-Cause Hospitalizations During Pulmonary Artery Pressure-Guided Therapy for Ambulatory Heart Failure” in Circulation: Heart Failure. The authors found significant reductions in the rates of heart failure and all-cause hospitalizations with risk reduction of 57% and 27%, respectively. The data were analyzed using the Andersen-Gill method for analyzing recurrent events, and events were recorded as before versus after the intervention (CardioMEMS insertion). There seems to be a major limitation that we did not find reported in the article or supplementary material. By design, patients only underwent implantation of the CardioMEMS device if they had at least 1 heart failure hospitalization in the 12 months before the sensor implantation. Therefore, the pre-CardioMEMS hospitalization rate will be at least 1.0 for all patients for the 12 months before the implant. In general, after an index heart failure hospitalization, about half of the patients would be expected to be rehospitalized in the following 12 months. Based on the Get With The GuidelinesHeart Failure, the 1-year rehospitalization rate is 57.9%.3 Therefore, if receiving the intervention is predicated on being hospitalized at least once in the prior 12 months, and this is also the outcome being measured, it should be expected that the rehospitalization rate will decrease after any intervention. This requirement of hospitalization in the year before the intervention is a bias in favor of any intervention. Was this accounted for in the statistical analysis? If not, should this reported reduction in rehospitalization be ignored?