Is there a U shaped curve relating exercise volume and risk of atrial fibrillation?

 RS Mishima (1) et al reviewed fifteen studies with a total of 1,464,539 individuals from databases of prospective cohort studies to determine the risk of atrial fibrillation (AF) at various exercise levels compared with those individuals who did not meet guideline recommended activity levels.

The current exercise recommendation are at a minimum 450-500 met minutes per week.However, both the US panel and more recently WHO have also said that higher levels, i.e. 2 or 3 times that amount will likely results in greater health benefits. The health benefits are apparent in large epidemiology studies which have demonstrated a curvilinear relationship between exercise volume  and reduction in cardiovascular and all cause mortality.

500 met-minutes per week is equivalent to 2 1/2 hours of moderate (less than 7 METs) exercise or 1 1/4 hours of vigorous exercise. 

While studies of long time athletes have generally shown longer longevity there have also been reports of an apparent increased risk of atrial fibrillation (AF) in endurance athletes particularly those who exercise at levels many times the minimal recommended level .

Mishima found that at exercise levels up to the 2000 met minutes per week level  ( four times the minimal recommended level )there was a decreased risk of AF but "past that point the benefit is less clear".At levels less than 2000 there was a 6 -11% lower risk of AF. At least in this study the upward arm of the U was not found.

 

(1) Mishima,RS  et al Self reported physical activity and atrial fibrillation risk: A systematic Review and Meta-analysis, Heart Rhythm 2020 Dec. 18 

Octogenarians and exercise capacity

 The average 80 year old who is healthy has a maximal oxygen capacity of about 20 ml.kilo/min. This is sufficient exercise capacity to finish stage 1 of the Bruce treadmill protocol which requires a 02 uptake of about 17.5. A 02 max of 20 should allow an orthopedically competent  person to walk a mile in 16 minutes. 

The 02 max value of 17.5 ( or 5 Mets) has been quoted as being necessary to be able to handle independent living and a value of less than 7  (2 Mets)  has been considered  considered incompatible with life. (I have been unable to find a reference that confirms that value )

The stylized story of maximal 0xygen uptake (V02 max) and human aging is something like the following:

V02max, heart rate and fat free weight begin to decline around age 25. Multiple studies have demonstrated that the average per decade decline in V02 max is about 9 - 10% while some data suggest that with continuing physical activity the decline may be only 5 % per decade (1)

However, the rate of decline appears to greatly increase after age 65 or 70 as the   curve  becomes curvilinear

Trappe et al studied 55 former elite distance runners after a 22 year period. Their data confirm earlier studies indicating there is a 5-7% per decade  decrease in aerobic capacity even in highly trained athletes. They also found that the subset who did not exercise regularly had a greater percentage decrease in V02max.

Viewed from beneath  the apex there is a systolic counter clockwise rotation of the apex and a clockwise rotation of the base of the heart, likening to wringing out a wash cloth. During diastole there is an untwisting most  of which occurs during the isovolumic relaxation phase of the heart (IVRT).This untwisting represent elastic recoil which is said to be due to the release of restoring forces.Decrease in this suction generation is thought to paly a role in so called diastolic heart failure ., now referred to as heart failure with preserved ejection fraction (HFpEF)

 However, data from Ben Levine's group at the Institute for Exercise and Environmental Medicine in Dallas  indicate that while there is some preservation of left ventricular compliance in those with a history of lifelong exercise ( defined as 25  years or more)  an increase  in IVRT occurred in both  the exercisers  and in the sedentary group.So Levine's data indicate that 4-5 hours of aerobic exercise per week maintained over " a lifetime" will preserve to a significant degree left ventricular compliance but not the prolongation of LV relaxation which accompanies old age.

Tanaka and Seals (3)  in their review article challenge Trappe and other researchers who hold the generally accepted position that regular aerobic exercise will blunt the age related decrease in v02 max. Less controversially  they  suggest that the decline in V02 max is mostly likely due to an age related decline in stroke volume. If  V02  =SV x HR x A-V 02 difference and they claim that there is not a significant decrease in maximal HR  nor AV 02 difference with aging, then only suspect variable left is the stroke volume.

A decreased stroke volume with exercise ties in nicely with the observation that the left ventricular relaxation ( as measured by AVRT  which is the time between aortic valve closure and mitral valve opening) is increased even in highly trained older endurance athletes. With prolonged relaxation time there would be less time for ventricular filling with the increased heart rate associated with exercise , so there is  less LV filling with each cardiac cycle leading to less ability to increase stroke volume with exercise.Add to that the decreased compliance of the left ventricle that occurs with sedentary aging and we can understand at least some of why V02 max decreases with aging.

However, there is more at work with the decrease in exercise capacity related to aging tha nthe decrease in  V02 max.One interesting data point in that regard is the observation that Ed Whitlock marathon times decreased from age 70 to age 82 with there being no change in his measured V 02 max.

At age  70  Whitlock  ran a 2:54 marathon and at age 82 his marathon time decreased to3:41This is a change  from  6.62 minutes per mile to 8.4 minutes per mile or a change from  9 miles per hour to 7.11 miles per hour, a 20% decrease.  Yet during that same time period his measured maximal oxygen uptake was unchanged. We also know from  published interviews  that his training did not significantly diminish. So what was the cause(s) of his decreased running speed?

1)Pollack, ML et al Twenty-year follow-up of aerobic power and body composition of older track athletes

J of App Physio 82 (25) 1508

2) Trappe, SW Costill,DL et al Aging among elite distance runners: a 22 yr longitudinal study

J of App Physiol Vol 80 no 1 285 1996.

3) Tanaka,H Seals,DR Invited review. Dynamic exercise  performance in Masters athletes Insight into the effects of primary human aging of physiological functional capacity.  J of Appl Physiology 2003 vol 95 no 5 2152

So should octogenarians doff their masks and not worry?

 The CDC guidelines now say that for persons who are fully vaccinated they can do most anything mask less. Did the CDC mean everyone ?

Did CDC mean that the  recommendation apply to adults of all ages and what about the immunosuppressed? No, not  for the immunocompromised, but I heard no special mention of the  elderly.

Was there find print in the CDC guidelines? Did everyone just hear the headline?

In general terms both the innate and adaptive arms of the immune system are impaired as a function of age. We know that the flu vaccine, for  example is less immunogenic in the  elderly ,What does fully vaccinated mean for the elderly in particular the 80 and over crowd as relates to covid19 vaccination?

Recently published data addresses that question.

Muller et al (1) conducted a cohort study on subjects less than 60 years of age and those over the age of 80 who received the Pfizer vaccine. Specific IgG antibody tiers against SARS-COV-2 spike protein were lower in the elderly and the elderly had no detectable neutralizing antibodies. In the younger group 2.2% had no detectable antibodies.

A large Danish Cohort study (2) compared vaccine effectiveness in health care workers and long term care patients. After the second dose the effectiveness in the patients was 64% ( 95% CI  14-84) while in  health care workers the   effectiveness was 95% (95% CI  82 -95. The median age of the 39 040 patients was 84 and there were 488 PCR confirmed cases of SARS-COV 2 cases. If this study can be generalized the widely quoted 90 % plus vaccine effectiveness does not apply to the elderly.

So how safe is it for fully vaccinated octogenarians to toss their masks? Is there risk for the 30% who have no  neutralizing antibodies. Going mask less assumes than only the fully vaccinated are going to go mask free? How valid is that assumption. Viewing baseball, hockey and basketball crowds televised from areas in the country in which there is at most 40 % vaccination rate and seeing everyone without a mask leads me to think not very valid.

The Danish and German studies are not the final word but , in my opinion, are sufficient for the over 80 crowd to consider it may not quite be time to throw the masks away and join the crowds.

It has been estimated there are 6 million immunosuppressed patients in the US? How effective are the Covid 9 vaccines in that group? There are sub groups, including organ transplant patients,patients with IBD and with psoriasis and lupus etc  who may be on medications impairing  the immune system. There are also patients on chemotherapy for various hematologic diseases. 

Data is available indicating that some of these patients do not have adequate vaccine mediated immune responses.? A large study from Johns Hopkins found that 46% of solid organ transplant patients had no response to covid19 vaccination. A study from Mt Sinai in New York found good immune response in IBD patients on therapy.

Both the CDC and the FDA have not recommended checking antibody levels nor getting a booster shot if the levels were low or absent. The American Society of Transplantation also agree with that position. Their reasoning escapes me. 

Addendum 6/23/2021 A more optimistic view of the effectiveness of Covid 19 vaccination in the elderly is found here. The article describes national  surveillance data regarding the administration of the Pfizer-BioNtech mRNA vaccine.They report effectiveness of 95.2 to 97.6  %for symptomatic cases in people 85 years of age or older. I am not able to offer an explanation of the large  discrepancy between this study and the Danish data. 

Addendum: 6/26/2021 As of at least 6/25/21 The health authority in Israel has reissued the indoor mask mandate following some cases reports of Covid 19 in fully vaccinated people .At about the same time WHO has stated that immunized people should wear masks  based on concern of the widespread incidence of the Delta ( India) variant. 

1)Muller,L et al Age-dependent immune response to Biotech/Pfizer BNT 162b2 COVID-19 vaccination Clin infectg Dis 2021 Apr 27

 2)Moustsen-Helms,IR et al Vaccine effectiveness after 1st and 2 nd dose of the BNT162b2 Covid-19 Vaccine in long term care facility residents and healthcare workser A Danish cohort study. Pre Print from Medrxiv 09 March 2021.

 

More evidence that the IPhone 12 can significantly impact pacemakers and ICD function

 Dr. Fahd Nadeem and colleagues at Brown University Cardiology studied the effects of the Apple iPhone 12 Pro max model on several pacemakers and ICDs made by Medtronic,Abbott and Boston Scientific, (1)

The iPhone 12 uses a charging device than can charge  wirelessly. It uses a charging bases that generates a magnetic field inducing voltage in the cell phone,

Nadeem demonstrated that placing the iPhone 12 directly over the CIED ( within 1.5 cm  of the unit ) inhibited the  capacity of the ICD to deliver a shock and when placed over a pacemaker caused  the unit to switch to an asynchronous mode.

CIED units are designed to respond to a magnet placed over the unit.It is a feature  and not a bug. An ICD is designed to respond to magnet application by "activation of the magnet mode" which mean that a certain pacing rate is set and the the tachytherapies are inhibited. Simply put, the ICD will not deliver a shock. Pacemakers are designed to respond to a magnet by reverting to a asynchronous pacing mode at a certain rate.The standard donut magnet is sometimes used in surgery when radiofrequency energy is used for cauterization.

Models manufactured by Medtronic and by Abbott  responded to the iPhone as described above but  models from Boston Scientific seemed less susceptible to the magnetic effect of the iPhone.

Magnetic mode activation has been reported to occur with as little a a 10G field magnet.The authors tested the IPhone 12 with a magnetometer and found a magnetic field of  50G.

An earlier study quoted by Nadeem found that an earlier model of iPhone did not trigger magnet mode reversion .

Take home message seems to be do not put an iPhone 12 in your breast pocket if you have a pacemaker or ICD.

Nadeem 's study appears to contradict Apple's advisory stating that the iPhone 12 does not pose a greater risk of magnetic interference than older generation of iPhones. Apple has made a variety of Phones  and the Nadeem article only provided data on the iPHone 12 and by reference the iPhone 6. 

1) Nadeem,F Magnetic interference on cardiac implantable electronic devices from Appl, iPone MagSafe Technology J Am Heart Jan 12 2021. e020818  (full text available)