Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What: Shares of defibrillation and CPR gear specialist ZOLL Medical (Nasdaq: ZOLL) plummeted today, falling as far as 30.7% on about 10 times their average trading volume.

So what: ZOLL reported earnings last week, sending shares sky-high on terrific sales of the up-and-coming LifeVest wearable defibrillator. Today, ZOLL filed the accompanying 10-Q statement with a new risk factor related to that hot seller: Medicare might not reimburse LifeVest purchases as often as previously assumed.

Now what: The new risk language portends that a recent change to Medicare policies "would limit the indications for Medicare reimbursement for the LifeVest product." Taking the wind out of the sails of ZOLL's hottest product would be terrible for growth projections. But don't cry for ZOLL investors just yet: The stock has still gained more than 80% over the last year after deducting today's crash, which handily beats the market as well as medical device rivals Boston Scientific (NYSE: BSX), Medtronic (NYSE: MDT), and even red-hot robotic surgeon Intuitive Surgical (Nasdaq: ISRG). The LifeVest isn't dead, just a bit tighter than we thought.

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