The dose of Atenolol you are taking seems to be appropriate for you. Had a doctor simply given you the same dose as a patient with an entirely different heart problem you would have trouble standing up at all. It does happen, and I've seen it.
Unfortunately, cardiologists tend to see their job as keeping your heart beating as long as possible, regardless of what is taking place in other organ systems, or what restrictions they place on your activity. There's a reason your heart began behaving weirdly in common situations, and we don't have an answer for why.
This brings us to a second blind spot in cardiology: recognition of degenerative processes prior to explicit heart damage. Part of this has to do with the drastic nature of the surgical interventions which are a major (and lucrative) part of the profession. About all they can do otherwise is to keep blood pressure or heart rate from going too high, or prescribe statins for evidence we are forming atherosclerotic plaques. Many of us have trouble tolerating statins and/or medication for bp.
Despite many advances in the field, the ability to predict trouble prior to a heart attack or catheterization is still poor, in the absence of an annual echocardiogram and stress test. (These are required if your business has a multi-million dollar insurance policy on you as CEO. None of us here are likely in that situation. You can be sure the CDC will oppose such diagnostic tests because of cost.)
Since we are likely to have low bp, we are not considered at risk. Diffuse problems with endothelial function are likely to be dismissed as trivial right up to the point where a blockage is detected and bypass is needed. (To the man who has only a hammer everything is either a nail or nothing.) Endothelial problems also affect the parts of the circulatory system inside the heart. While the muscle is fine on the systole it may be slow to relax during diastole. This results in reduced filling and reduced stroke volume. Measuring stroke volume accurately is tricky. This is where we run into the medical tendency to cast things in dichotomies based on thresholds: either you have a problem I need to do something about, or you don't have a problem at all.
At one time diastolic dysfunction was considered a minor problem, and you can probably find cardiologists who have not changed their opinions. Research now shows that
serious left-ventricular diastolic dysfunction is just as lethal as systolic dysfunction. Either one strongly predicts death within 3 years without intervention. Most of us fall in the category of mild diastolic dysfunction,
which is not associated with increased mortality on that time scale. This is the point where cardiologists generally tune out. Whatever is wrong with us is somebody else's problem.
You can probably see the catch here. We aren't going to die as long as we don't push ourselves far beyond our limits, but our limits are unusually narrow. If the condition is progressive there is a real danger to life, but we have apparently fought the pathological process to some kind of impasse. Many of us performed much, much better prior to onset, but we were not studied at that time. If a doctor had followed those changes the condition might have been considered progressive, until it leveled off after six months or more. With current definitions it is effectively impossible to study ME/CFS patients in that significant interval.
All I've said here is the opinion of an educated layman. I've concentrated on heart function because that is where the discussion was going at the time. I want to emphasize that none of us, doctors or patients, know what causes the dramatic change in function so many of us have experienced. These changes affect the heart, but are certainly not limited to it. You can find weird stuff going on in a variety of organ systems.
From my own perspective this illness resembles sudden aging. People in their teens, twenties or 30s, suddenly behave like they are 40 years older. It is likely the relevance to the rest of the population will be that it illuminates the processes which make aging degenerative. I strongly suspect this will shed light on the causes of "serious diseases" like heart problems which are now poorly predicted in the general population.
