Indianapolis-based health insurance giant WellPoint Inc. on Monday named a new chief of its Medicare businesses in hopes of reversing recent struggles in that key sector.

Venkata Rajamannar Madabhushi will take control of the various Medicare Advantage plans WellPoint runs around the country, replacing Brian Sassi, whom WellPoint fired last month. Rajamannar will also oversee WellPoint’s international, marketing and product innovation divisions, as well as its corporate development functions.

WellPoint is staking much of its future on serving beneficiaries of Medicare, the federally funded health insurance plan for seniors. Enrollment in Medicare is predicted to grow rapidly as baby boomers retire, even as employer-sponsored health plans stagnate or shrink.

In June, WellPoint agreed to pay a reported $800 million to acquire a West Coast Medicare business called CareMore. But problems in a California Medicare plan last year cost WellPoint $150 million, and analysts are worried the problems are not contained for 2012.

Sassi remains at WellPoint to help with the transition until Rajamannar gets up to speed.

Rajamannar will not oversee WellPoint’s Medicaid and individual insurance plans, as Sassi did. Instead, those divisions are now headed up by Ken Goulet, who is CEO of WellPoint's commercial business unit.

Before joining WellPoint, Rajamannar, who goes by the nickname "Raja," served as chief innovation and marketing officer at Humana Inc., a WellPoint competitor based in Louisville. He also spent 15 years in senior-level business management and marketing roles at Citigroup.

"Raja’s extensive experience in global business management, marketing, product development and consumer engagement will be a great asset to our company, especially at a time when consumers are taking a more active role in the selection and management of their health care options,” WellPoint CEO Angela Braly in a prepared statement.