Adds details about procedure forecast in paragraphs 8 and 9, updates share price in paragraph 6

By Michael Erman and Puyaan Singh

July 15 (Reuters) - Johnson & Johnson JNJ.N said on Wednesday that its medical device unit underperformed in the second-quarter, even as strong sales of Tremfya for autoimmune conditions and cancer treatment Darzalex helped it beat Wall Street estimates.

U.S. demand for its Impella heart pumps, acquired through its $16.6 billion 2022 buyout of Abiomed, dropped during the second quarter by 2% after having grown 14% during the first quarter, it said.

CFO Joseph Wolk said in an interview that Abiomed revenue took a hit following the release of a U.K. study that raised questions about the use of Impella pumps during certain high-risk coronary procedures.

Wolk said J&J expects the franchise to return to growth, aided by additional data expected in the first half of next year that could further demonstrate the usefulness of the pumps.

"When you have 28 platforms that generate at least $1 billion in revenue on an annual basis, we're not dependent on one asset," Wolk said.

Shares fell 0.4% to $252.80 in morning trading.

BROAD MEDTECH DEMAND STABLE

Still, the company said it is not seeing evidence of a slowdown of procedures using its medical devices after Hospital operator HCA Healthcare HCA.N warned on Tuesday of weaker surgical volumes and more patients dropping out of Affordable Care Act plans. That pushed shares down in J&J and other medtech companies such as Stryker SYK.N and Intuitive Surgical ISRG.O.

"Procedure volumes continue to be stable," J&J Executive Vice President Tim Schmid said on a conference call with investors. "We have not observed any meaningful impact on procedure volumes across our portfolio related to the ACA."

Sales at J&J's medtech unit came in at $8.93 billion, below analysts' average estimate of $8.97 billion, according to data compiled by LSEG.

"Overall medtech procedures were solid as shown by strength in ortho, vision and stability in surgery," Evercore ISI analyst Vijay Kumar said.

Kumar said the results could help ease concerns around broad demand for medical devices.

RAISES ANNUAL SALES FORECAST

J&J's second-quarter sales grew nearly 7% to $25.31 billion, above analysts' average estimate of about $25.05 billion.

The pharmaceutical unit helped boost total sales. It generated $16.38 billion in quarterly sales, ahead of analysts' estimate of $16.1 billion.

Adjusted earnings per share stood at $2.90, topping expectations of $2.85.

The company now expects annual sales of about $101.1 billion at the midpoint, compared with $100.8 billion previously. It also raised its adjusted earnings per share forecast to $11.68 at the midpoint, from $11.55 previously.

Sales of its psoriasis and inflammatory bowel disease drug, Tremfya, jumped 72.5% to $2 billion, well above estimates of $1.74 billion. Tremfya has become increasingly important as J&J works to replace lost sales from Stelara.

Revenue from Stelara, which treats psoriasis, Crohn's disease and other autoimmune conditions, fell over 55% to $740 million in the quarter.