Earnings season isn't over, but the quarters from health care companies that have already reported have given us a great look at how the medical device sector's faring. Numerous companies have reported good results, but one constant remains: The cardiac rhythm management, or CRM, industry -- which handles everything from pacemakers to defibrillators -- is facing off with a tough market. Sales are falling across the industry yet again, perpetuating a worrying trait that hasn't eased up after tough results in the third quarter of 2012, as well.

Is there hope for a turnaround for companies in the CRM space, or is this an industry on the decline that you should keep your investment far away from?

Sales on the decline Just a few years ago, the CRM market was on the rise, growing by double digits. Now, however, the market across the world has dried up -- in both the U.S. and internationally, sales are falling for CRM products.

St. Jude Medical, Inc. (NYSE:STJ) has traditionally been among the powers in this business, but the company's reliance on CRM sales has come back to bite it. St. Jude's CRM division supplies around 50% of total company sales, and when that division's suffering, it's tough sledding for the company.

St. Jude's CRM department has already been on the downslide, with sales falling 4% on a constant currency in the third quarter -- a significant year-over-year slide. With the company's full-year results now out, we can see just how hard the division has fallen: CRM sales at a constant currency fell 5% year over year in St. Jude's fourth quarter, near the high end of the business' guidance, with sales down 3.5% over the course of the full year.

Fortunately, St. Jude's largest segment in the CRM business -- its ICD (or implantable cardioverter defibrillator) segment -- hasn't been hit quite as bad. Currency issues have really plagued this business, as the ICD segment only lost 2% over the course of the year at a constant currency. Falling pacemaker revenue has really hit St. Jude hard, but this company is hardly alone in its CRM troubles.

Boston Scientific Corporation (NYSE:BSX) doesn't rely as heavily on CRM sales as its rival, but its sales are no less concerning. After losing 4% in its CRM revenue for the third quarter, Boston Scientific's business dropped another 4% in Q4 for a total loss of 7% year-over-year for 2012.

Even the industry's biggest major player, Medtronic, Inc. (NYSE:MDT) , has witnessed its CRM business losing sales, particularly among pacemakers. Things aren't so good in this sector, but why are sales falling -- and what should you account for in the future?