The "Dear Doctor" letter, notifying clinicians of interim results from its post-approval study on Impella RP, "adds a question mark" to the Abiomed story, William Blair analyst Margaret Kaczor tells investors in a research note. However, from a fundamental perspective, Impella RP has been a relatively small part of Abiomed's revenues, contributing approximately $6.6M in its fiscal Q3. Thus, the analyst believes Abiomed can continue to grow over 20% over the next several years without significant contribution from Impella RP. Kaczor keeps an Outperform rating on Abiomed.