At the start of the COVID-19 pandemic, heart surgeons warned that fewer people were coming in for bypass operations, valve replacements, and other cardiac procedures, in some cases dying as a result.

In a new nationwide analysis, researchers determined that the consequences may have been even worse than many realized — particularly in hard-hit hot spots in New Jersey, New York, and Pennsylvania.

During April, the number of heart surgeries plunged by 71% in those three states and by 53% in the country as a whole, when compared with monthly averages in 2019.

And those who did undergo heart surgery were less likely to survive it, according to the analysis, drawn from comprehensive data collected by the Society of Thoracic Surgeons.

The study did not identify reasons for the lower survival rates, but two explanations are likely, said lead author Tom C. Nguyen, chief of cardiothoracic surgery at the University of California-San Francisco:

Patients who did undergo surgery may have waited before seeking medical attention due to concern about the coronavirus — potentially resulting in worse outcomes, he said. And in those three Northeastern states, many hospitals were struggling to cope with the first surge of COVID-19, in some cases diverting intensive-care beds and personnel who were normally assigned to heart surgery and other complex medical conditions.

“Cardiac surgery is complicated,” he said. “There’s a routine and a cadence in what we do that involves a lot of moving parts. Sometimes, all it takes is for one or two parts to be off-axis, and other things can break down pretty quickly.”

Heart surgeons at two Philadelphia-area health systems said they saw no decline in their patient survival rates, yet agreed that the drop in the number of surgeries was unmistakable.

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Delaying surgery might have been OK in some nonemergency cases, provided that those patients came in later in the year to get it done, said Paul Burns, chair of cardiothoracic surgery at Deborah Heart and Lung Center, in Browns Mills, Burlington County. And sure enough, heart-surgery numbers have rebounded at Deborah and elsewhere in the region since April.

But the increase has not been enough to make up for the sharp drop in that first month, Burns said. That suggests some people never made it to the hospital.

“Probably a lot of people died who needed urgent care,” he said.

Basel Ramlawi, chief of cardiac surgery for Main Line Health and codirector of the Lankenau Heart Institute, agreed.

“Many of them, I suspect, were dying at home,” he said.

Both stressed that although it remains wise to be vigilant about COVID-19, no one should hesitate to seek medical help for chest pain and other signs of heart trouble. Hospitals have strict infection-control protocols in place, such as limiting visitors and isolating COVID patients from those with other conditions.

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“The risks of not coming in are much higher than the risks of contracting COVID,” Ramlawi said.

The number of heart surgeries in April was 20% lower than usual at Lankenau, Main Line Health’s primary location for heart surgery, and 50% lower than usual at Deborah, the surgeons said.

Ramlawi said Main Line’s decreased volume was not as pronounced as the decline for the region as a whole in part because most of its heart surgeries are minimally invasive. That means surgeons make a small incision through the rib cage instead of cutting open the patient’s chest, allowing for a faster recovery and, with less time in the hospital, less potential for disruption due to the COVID-19 surge, he said.

The percentage declines at those hospitals (and in the study) include both emergency heart surgery and nonemergency cases, or what the study authors called elective. That makes it sound as if the patient has a choice in “electing” to undergo surgery, but what it really means is that the procedure was scheduled in advance — as opposed to an unplanned surgery that took place after a trip to the ER.

While the numbers for both types of surgery declined in April compared with the monthly averages for 2019, the drop in elective, nonemergency surgery was higher, in part because physicians counseled patients to postpone them when it was medically advisable, the study authors said.

In Pennsylvania, New Jersey, and New York, for example, the number of elective surgeries dropped by 75% in April, while the number of nonelective procedures dropped by 59%, for an overall drop of 71%.

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The impact on patient survival was measured as a ratio between observed number of deaths to the expected number, based on the type of procedure and characteristics of the patient population. Patients at hospitals in Pennsylvania, New Jersey, and New York generally fare better than expected, meaning their mortality ratio is less than 1.

But during the April COVID-19 surge, the region’s ratio climbed above 1, as did the ratio for New England, another early hot spot. In the two regions combined, the mortality ratio climbed from about 0.7 in February to nearly 1.2 in April, the study authors found. The findings were presented Jan. 30 at the annual meeting of the Society of Thoracic Surgeons.

The heart-surgery numbers were tallied only through June, and do not include the fall and winter, when the second surge of COVID-19 was, in many parts of the country, even worse than in the spring.

Yet anecdotal evidence suggests that hospitals managed better the second time around, said Nguyen, the study author. Hospitals now have more reliable supplies of protective equipment, and they have established routines to reduce the risk that heart-surgery patients could be exposed to COVID-19.

As in April, the most important takeaway for the general public remains the same, Nguyen said. In cases of chest pain or tightness, unexplained arm pain, or other signs of a heart attack or other cardiac trouble, seek immediate help. And remember that for women, symptoms of a heart attack may be different, including other signs such as nausea.

“The hospital,” he said, “is still the safest place to be if you’re sick.”