A longtime reader who was a senior official government in a previous Democratic administration sent me this:

I’m sorry if this question strikes people as impolite. A 78-year old man who had a heart attack less than five months ago and refuses to release his complete medical records is the frontrunner for the Democratic presidential nomination. If Bernie Sanders is nominated and elected president, what are the odds he can complete a full term? The answer is about 50-50.

A team of nine cardiologists recently published a study in the Journal of the American Heart Association that can help answer that question.Their study tracked the expected mortality and life expectancy of people who survive a first heart attack (myocardial infarction) at ages 65 and older. The scientists’ data are comprehensive, covering what happened to 22,295 heart attack patients admitted to U.S. hospitals from October 2004 to December 2006.

Their analysis provides two ways to estimate a person’s expected mortality and life-expectancy based on age and cardiac history. Both methods produced nearly identical results. The likelihood that a person of Senator Sanders’ age and heart history will die within one year – that takes us through September 2020 – is 25 percent. Further, the median period of survival for those patients is about five years, so the likelihood that someone of Senator Sanders’ age and heart history will survive through the next presidential term is about 50-50.

This is far from typical. According to the CDC, the odds that a 78-year old American will die within one year are just over 4 percent, and the odds over five years are less than 23 percent. Moreover, 45 people have served as President of the United States, and four of them died in office from natural causes. The historical likelihood that a president will die in office for medical reasons, therefore, is less than 9 percent.

The analysis of Senator Sanders’ prospects could be more precise than 50-50, if we knew a common indicator of his current cardiac status, called the “the left ventricular ejection fraction.” This measures the blood volume a person’s heart pushes out with each heartbeat. According to an interview by NBC News with the president of the American College of Cardiology, Dr. Richard Kovacs, the results are closely associated with a patient’s expected mortality rate. By this measure, the normal blood volume level is 60 percent. At 40 to 50 percent, the functioning of the heart’s left ventricle is said to be mildly impaired; at 30 percent to 40 percent, moderately impaired; and at 30 percent or less, severely impaired.

It is certainly reasonable that voters know those results for a 78-year old potential nominee with a heart condition. Thus far, Senator Sanders has refused. If he persists and is nominated, voters will have to consider very carefully his choice for vice president, since the odds that a vice president would succeed a President Sanders for medical reasons during his first term will jump from an average 9 percent to 50 percent.