Shares of

Medtronic

(MDT) - Get Report

dropped by more than 9% Thursday as analysts reacted grumpily to the announcement late Wednesday that growth had slowed for a key product and that third-quarter revenue would fall slightly below previous estimates.

Medtronic's official quarterly financial report will be released Feb. 11.

Only one investment banking firm -- CIBC World Markets -- cut its rating on Thursday; but some other analysts began re-evaluating earnings and revenue projections due to Medtronic's news about implantable cardioverter defibrillators, or ICDs. These devices deliver electrical therapy to treat heart rhythm disorders.

Medtronic's stock closed Thursday at $47.25, losing $4.75 a share, or 9.1%. The stock fell as low as $46.83.

CIBC's John Calcagnini dropped his rating on Medtronic to sector underperform from sector perform. "Last night's pre-announcement will likely serve as a big disappointment to

Wall Street," the analyst said in a prophetic early morning research report to clients.

In December, the company said third-quarter revenue could be at the high end or even exceed a range between $2.15 billion and $2.23 billion. But the company said Wednesday that revenue for the quarter ended Jan. 31 would be a shade under $2.2 billion, based on preliminary figures.

Calcagnini said his conversation with company officials led him to speculate that Medtronic "may be backing off" its third-quarter earnings per share guidance of 40 cents to 41 cents. He cut his quarterly EPS estimate by a penny to 39 cents.

He also cut his full-fiscal year EPS prediction by 2 cents to $1.60. He doesn't own Medtronic shares; his firm doesn't have an investment banking relationship with the company.

"Ugh" was the headline for a Thursday report by Prudential Securities analyst Robert Faulkner, who kept his underweight rating on Medtronic's stock. He said this would be the third consecutive quarter for which the company had missed revenue estimates for the ICD market. He said the ICD revenues would be $462 million, or $18 million below his estimate.

Several other ICD makers recently have missed quarterly estimates, too, he said. Faulkner doesn't own shares; his firm doesn't have an investment banking relationship with Medtronic.

Minneapolis-based Medtronic said late Wednesday that despite the slowdown in ICD growth, the "long-term market prospects" for ICDs and other heart rhythm management products "continue to be positive and that the ICD market has the potential to grow about 20% over time."