With a weak heart muscle and heart valve problems, Ruben Rivera said he was apprehensive about having a new type of battery-powered defibrillator implanted under his skin that could shock his heart if it sensed an irregular rhythm.

But the 62-year-old San Antonio resident has no regrets since becoming the first patient here to undergo the procedure late last month.

“I feel good,” said Rivera, acknowledging that while his heart is still weak, “I have peace of mind, which makes it feel that much better.”

“I know that if I go into cardiac arrest, this apparatus will take care of my needs,” he told the San Antonio Express-News (http://bit.ly/1k5PdBi).

Rivera is one of hundreds of thousands of patients in the United States that have cardiomyopathy, or a weak heart, which puts them at a higher risk of dangerous abnormal heart rhythms, said Dr. Manoj Panday, director of cardiac electrophysiology at the University of Texas Health Science Center.

Cardiomyopathy can be caused by coronary artery disease, a prior heart attack, a viral infection or an adverse reaction to certain medications, Panday said. Hundreds of thousands more people in the United States may be at risk of life-threatening ventricular arrhythmias, he said.

“Having a defibrillator that’s there as an insurance plan, so to speak, is important because it helps to protect them whenever it may occur but at the same time allows them to live a normal life and not have to think about the defibrillator,” Panday said. “It’s there doing its job silently all the time.”

Panday implanted the new device, created by Boston Scientific and called a subcutaneous internal cardioverter-defibrillator, or S-ICD, in Rivera last month at the Audie Murphy VA Hospital. The company selected the initial physicians for the procedure based on their experience and ability to offer this type of care to patients, he said.

The S-ICD is implanted in the chest wall, Panday said. The traditional implantable defibrillator required puncturing a blood vessel and screwing an electrode or lead into the heart to conduct the charge, he said. The new device was designed to avoid some of the resulting risks, which include puncturing the lung or the heart or introducing bacteria that could cling to the defibrillator and cause a serious infection.

Rivera was a good candidate for the new device because a previous surgery had caused a bacterial infection that entered his bloodstream, Panday said.

At University Hospital on Monday, Panday implanted another such device in Leonardo Perez, 50, of San Antonio.

Perez said he had triple bypass surgery last year and felt lucky to benefit from the new technology.

“Let’s get going,” he said, eager to get the hour-long procedure underway. “I’m ready.”

Once Perez was sedated, Panday cut a pocket a few inches below his left armpit to insert the generator, which is about the size of a deck of cards.

Using two small incisions, Panday ran the lead — a thin, insulated wire — across from the pocket to the center of the chest and then up the chest. The device can deliver 80 joules to the chest wall, “much like you see on a television shows where a doctor will say, ‘Stat,’ and shock a patient with paddles,” Panday said.

The battery lasts about five years before the generator needs to be replaced in an outpatient procedure. The battery runs down faster than the traditional defibrillator because it requires a greater charge — it’s not as close to the heart.

The tensest moment of the procedure came after the device was inserted in the chest. Panday and his team tested it by inducing a cardiac arrest and then watching as the device sent a shock trembling through Perez’s still unconscious body, jolting his heart back into a normal heart rhythm — ready to save his life should he need it again.