A closer look at Red Sox pitcher Eduardo Rodriguez’s struggle with myocarditis

Eduardo Rodriguez couldn't pitch at all this season after making a major league-high 34 starts in 2019.Jim Davis/Globe Staff

On the surface, it’s difficult to reconcile what Eduardo Rodríguez has been doing in 2020 with the idea of what he’s hoping to do in 2021.

It’s not merely that Rodríguez proved unable to pitch for the Red Sox this year after testing positive for COVID-19 and subsequently being diagnosed in late July with myocarditis, an inflammation of the heart muscle. Once the pitcher was sent home to South Florida at the beginning of August, he was told to stop all exercise, including walks outside the house.

He had more than two months of total inactivity leading up to his reexamination in Boston in late September. As of that time, the team anticipated that in a best-case scenario, it wouldn’t be until at least mid-October that he could start engaging in light exercise on a treadmill.

The reason for caution is obvious. The consequence of stressing the heart when myocarditis is present isn’t merely a threat to a career. It is a potential threat to life.

That worst-case scenario informed a corresponding response, chiefly having Rodríguez avoid physical exertion for a period of three months. Yet despite that restriction — which spanned the 2020 season — the Red Sox and Rodríguez are optimistic about the pitcher’s outlook. He’s expected to have a normal offseason and considered likely to be ready for the start of the 2021 season.

“I was confident, first of all, listening to the doctors that were handling Eduardo and finding out that he was under real good care,” said Rodríguez’s agent, Scott Pucino of Octagon. “Even though it’s frightening to hear about the heart, you know that the care that the Boston Red Sox had with the cardiologists, how confident they were that, hey, shut this down and things will be OK."

Despite that assessment, Rodríguez offers a reminder of the uncertainties that accompany the coronavirus. After all, after testing positive for COVID-19 before reporting for training camp in July, the 27-year-old lefthander was cleared to join the team following multiple negative tests in July.

He’d been able to throw into a net during his quarantine, and once in Boston, had thrown two bullpen sessions while trying to prepare for the season. But fatigue in the second of those sessions at Fenway Park led to the MRI that resulted in the diagnosis of myocarditis.

Much remains unknown about the relationship between COVID-19 and the cardiac health of athletes who are attempting to return to play. Medical researchers are still trying to gain insight into the impact of the virus on cardiac health and the frequency in both the general population and athletes of such impacts.

As such, the effort to define the best practices for how to ensure the safe return of players coming back from COVID-19 infections to their sports remains ongoing.

“There’s still so much of a mystery with COVID in general," said Dr. Jonathan Kim, the chief of sports cardiology at Emory University. “We’re left in this very challenging arena where we obviously know COVID can impact the heart in hospitalized patients. We’re worried about the potential impact on athletes because if myocarditis is present, myocarditis is a common cause of sudden death. Adverse events can happen if you intensely exercise and there is active inflammation in the heart. But there are all these unknown questions as it relates to how much cardiac injury occurs in patients, including athletes, who are not as sick with COVID or may have an asymptomatic infection.

“Hopefully sooner rather than later we’ll have a better idea about how much cardiac injury occurs in athletes who are not as ill with COVID-19. We will learn about the effectiveness of our current screening procedures. We’ll let the science drive us. But in terms of the evidence and published science out there right now, the data are pretty minimal and limited right now.”

Eduardo Rodriguez watched a Red Sox intrasquad game from a Fenway Park suite in July.Jim Davis/Globe Staff

The limited data pool in turn means that there isn’t a definitive playbook to follow, a notion acknowledged by the Red Sox in the case of Rodríguez.

“There’s no precedent for this,” chief baseball officer Chaim Bloom said at the end of the season. “There’s such a limited history of athletes with myocarditis, there’s no history of athletes with COVID myocarditis, and we need to make sure we’re putting Eddie’s health first and foremost.”

The Red Sox appear to be following standard practices for treating athletes who experience myocarditis that isn’t the product of COVID. The prescription of three months of rest is standard for athletes diagnosed with myocarditis. For now, that same period of inactivity — which Kim said yields a full recovery of the heart in the majority of cases — is being prescribed for those who develop myocarditis after testing positive for COVID-19.

“Although uncertainties persist, our current recommendation is that if an athlete has to be restricted from sports due to clear cardiac involvement from COVID, we’re aligning with our current return-to-play myocarditis recommendations. Right now, there’s no evidence to say that you can’t try to get [athletes] back [to physical activity] once you get to that minimum three-month time line. We’re following that algorithm right now,” said Kim. “Now, for an athlete, three months away from sport is obviously a long time, so you’re going to have to have a slow, graded return to sport … But the myocarditis is resolved at that point. So really it’s just a matter of conditioning as long as the repeated testing shows the myocarditis has resolved.”

So long as Rodríguez is free of myocardial inflammation, it’s expected that he can begin a carefully regulated offseason strength and conditioning program in the coming weeks — starting with walking on a treadmill.

That step will represent a modest beginning, and increases in his conditioning program will occur incrementally. That said, with four months until the scheduled reporting date for spring training, a normal course of recovery from a three-month shutdown for myocarditis could still afford enough time for Rodríguez to be ready for the 2021 season.

The Red Sox won’t take that outcome for granted. Pitching coach Dave Bush spoke prior to the end of the season about the possibility that Rodríguez — who made a major league-leading 34 starts in 2019 while logging a career-high 203⅓ innings — might have workload restrictions in 2021 after not pitching this year.

Yet for a pitcher who found his inability to pitch wrenching — “Man, I really miss playing so bad,” he tweeted in August — the medical feedback has offered grounds for hope.

“[Rodríguez] is really excited, to be honest with you,” said Pucino. “He’s following a strict training regimen and just making sure he does whatever the doctors tell him to do. He’ll be ready, 100 percent. We’re very confident about that.”