After attending the Transcatheter Cardiovascular Therapeutics 2019 meeting, William Blair analyst Margaret Kaczor believes near-term dynamics and timing of a return to 20%-plus growth "remain somewhat unpredictable" as Abiomed moves into the next leg of Impella adoption. Following two weak quarters in a row, Abiomed shares have become a "show-me" story until the company demonstrates it can start to reaccelerate growth sustainably, Kaczor tells investors in a research note. The analyst, however, continues to believe that Impella penetration remains low at less than 15% and that the long-term thesis around hemodynamic support remains intact. She keeps an Outperform rating on Abiomed.