Chronic fatigue syndrome (ME/CFS) is considered a multi-system illness with dysfunction in the immune system, central nervous system and hormones. However, research is suggesting that the abnormalities don't stop there -- ME/CFS is being tied to several irregularities in the heart.
These irregularities include:
- Low nocturnal heart rate variability
- Small left ventricle (in one subgroup)
- Postural tachycardia
- Short QT interval
- Abnormal cardiac wall motion with exercise (in certain subgroups)
- Low blood volume & reduced cardiac function
These irregularities may be to blame for some of the key symptoms of ME/CFS. They may also point to the importance of working to maintain heart health to lower the risk of cardiac problems.
Low Noctural Heart Rate Variability
In a small 2011 study on the sleep-wake patterns of people with ME/CFS, researchers monitored overnight heart rate. They discovered low heart rate variability (HRV) in ME/CFS participants as compared to healthy controls.
If you feel your pulse and then breathe in and out slowly, you'll notice that your heart rate changes slightly, speeding up when you breathe in and slowing down when you breathe out. That's heart rate variability.
Low HRV can indicate either problems with brain and/or nerve signals going to and from the heart or a problem with a portion of the cardiac conduction system called the sinus node. Researchers hypothesize that the low HRV in ME/CFS is tied to the brain via the autonomic nervous system, which regulates the body's automatic functions. Dysregulation of the autonomic nervous system is called dysautonomia and is believed to be a feature of ME/CFS.
In the study, low HRV was directly linked to unrefreshing sleep, leading researchers to conclude that it's an important issue for further study.
Small Left Ventricle & Orthostatic Intolerance
The heart has four chambers -– a left and right ventricle and a left and right atrium. A 2011 study linked a small left ventricle with a subgroup of ME/CFS patients that have a symptom called orthostatic intolerance (OI).
OI makes people feel dizzy when they stand up. Normally, when we get up from a seated or lying position, the blood pressure rises briefly to counter gravity and keep the blood flowing properly to the brain. Someone with OI, however, experiences a dip in blood pressure upon standing. That makes them feel lightheaded and sometimes causes fainting (syncope).
The study suggested that people with OI have a small left ventricle that doesn't pump out as much blood as normal, and the trait was more pronounced in the people who had ME/CFS in addition to OI.
Researchers concluded that the small left ventricle may contribute to the development of OI and ME/CFS symptoms through low blood flow to both the brain and body. They also stated that ME/CFS+OI appears to be a well-defined and significant subgroup of ME/CFS.
Like low HRV, OI is believed to be related to dysautonomia.
Postural tachycardia is similar to OI except that it involves the pulse rate and not the blood pressure. It's also tied to dysautonomia.
Tachycardia is an abnormally rapid heart rate. Postural tachycardia means your heart rate speeds up abnormally when you stand. It's sometimes diagnosed as postural orthostatic tachycardia syndrome (POTS).
Postural tachycardia is common in people with ME/CFS. In a study of adolescents with ME/CFS, it was correlated with low vitamin D levels. Other studies have linked ME/CFS to vitamin D deficiency.
Short QT Interval
When you have an EKG (electrocardiogram), a common test of heart health, the machine maps out your heart's electrical cycle in a zig-zaggy line. To measure specific aspects of it, points on the line are marked with letters. Differences between certain points –- the intervals –- can provide information for your doctor.
The interval between the points marked Q and T is one of those that's sometimes important. A 2006 pilot study suggested that a short QT interval is rare in the general population but common in ME/CFS because of dysautonomia.
Abnormal Cardiac Wall Motion
The way the walls of the heart move can be an important indicator of cardiac health. Chronic fatigue syndrome researcher A. Martin Lerner, MD, has done multiple studies on abnormal cardiac wall motion (ACWM) in ME/CFS and, in his practice, tests cardiac wall motion (among other things) to gauge the effectiveness of treatment.
Lerner's work, however, is controversial and focuses only on ME/CFS subgroups of his own designation.
According to Lerner's 2004 study, ACWM is present in some cases of ME/CFS related to Epstein-Barr virus and/or cytomegalovirus. The study showed that 11.5% of people in that subgroup have ACWM when resting, compared to just 2% in a control group.
In a 2007 study, Lerner and colleagues suggest that the anti-viral drug valacyclovir decreased both ACWM and sinus tachycardia in ME/CFS patients with Epstein-Barr. This work has not been validated by other studies.
ACWM is sometimes linked to ischemia (impaired blood flow).
Low Blood Volume & Diminished Cardiac Function
In the earlier study, researchers said that those with severe ME/CFS had the lowest blood volume. Tests indicated that diminished heart function was likely a consequence of low blood volume and not due to structural defects in the heart.
Some ME/CFS doctors believe that low blood volume contributes to many symptoms of ME/CFS by depriving cells of the oxygen they need to produce energy. However, this theory has not been proven by research.
What It Means for You
In a small survey of causes of death among people with ME/CFS, researchers found that heart failure was a common cause of death among the cases examined, accounting for just over 20% of deaths. The mean age of death from heart failure was about 59, which is more than 15 years earlier than the mean for the greater population.
So far, we don't fully understand the contributions of possible cardiac abnormalities toward the causes of death for people with ME/CFS. Other things -- such as weight and sedentary lifestyle -- may be a part of the equation as well.
It's important to remember that most of these studies are small and have not been replicated, meaning we don't know a lot about these possible abnormalities or what they mean. A lot more work is needed for us to answer the questions these findings raise.
Meanwhile, the possibility of heart problems is something you may want to discuss with your doctor. Certainly, it's a good idea for everyone to be aware of heart hearth and try to minimize the risk of cardiac disease.
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