How Parkison’s disease affects the heart
It has long been understood that Parkinson’s disease (PD) does not just cause movement, or motor, symptoms, but also causes a litany of non-motor symptoms with effects throughout the body. One of the organ systems that is affected is the cardiac system, encompassing the heart, as well as the major and minor blood vessels.
Understanding the neurologic control of the cardiac system
Before we explore this connection between Parkinson’s disease and the heart, let’s first learn a bit about the autonomic nervous system (ANS) and about the cardiac system’s place within it. The ANS is part of the peripheral nervous system, a network of nerves throughout the body. The ANS exerts control over functions that are not under conscious direction such as respiration, heart function, blood pressure, digestion, urination, sexual function, pupillary response, and much more.
The ANS is further subdivided into the parasympathetic nervous system and the sympathetic nervous system. Both the parasympathetic and sympathetic nervous systems regulate most major organs. Often, they have opposite effects, with the sympathetic nervous system activating a system and the parasympathetic system calming it down.
One of the systems controlled by the ANS is cardiac regulation. Blood pressure sensors, known as baroreceptors, reside in the heart as well as in the carotid artery, the major artery in the neck. If the baroreceptors sense a change in the blood pressure, a signal is sent to particular areas in the brain. From there, the autonomic nervous system sends signals to the heart to control heart rate and cardiac output. Signals are also sent to the blood vessels to change the size of their diameter, thereby regulating blood pressure.
How Parkinson’s disease affects the autonomic nervous system and the heart
Neurogenic orthostatic hypotension (nOH)
In PD, there are two major reasons why the automatic control of the cardiac system is impaired. First, areas of the brain that control this system often contain Lewy bodies and have undergone neurodegeneration. In addition, the autonomic nervous system itself is directly affected by Lewy body-like accumulations and neurodegeneration. This means, when the baroreceptors in the heart and carotid artery sense a drop in blood pressure and try to generate a signal to the heart and blood vessels to increase the blood pressure, the message may not get through.
This results in neurogenic orthostatic hypotension (nOH), or drops in blood pressure upon standing due to autonomic nervous system dysfunction, in which case you may experience dizziness, blurred vision, and even fainting. While there are no medications that can cure nOH by restoring the autonomic nervous system in PD, nOH can be treated.
Read our factsheet about nOH and its treatments, and be sure to talk with your doctor if you are experiencing these symptoms.
Heart rate variability (HRV)
Typically, when discussing the cardiac effects of PD, the common focus is on nOH. However, another cardiac effect in Parkinson’s disease is changes in heart rate. Heart rate variability (HRV), which is a measure of the variation in the time interval between heart beats, was found to be less pronounced in patients who eventually developed Parkinson’s than those who did not, suggesting that cardiac autonomic dysfunction can be an early non-motor symptom of Parkinson’s disease.
A recent study demonstrated that Parkinson’s patients who have freezing of gait have more HRV than those who do not have freezing of gait. This observation implies that freezing of gait and autonomic dysfunction may be linked.
Other studies have shown that people with PD tend to have certain features on their electrocardiogram. These features include a prolonged PR interval and possibly a prolonged QTc interval, referring to longer than normal segments of the tracing of the heart. It remains unclear what the clinical consequences of these changes are, although they are not thought to commonly lead to cardiac rhythm abnormalities.
Cardiovascular disease and PD
The most common form of heart disease in the general population is not autonomic dysfunction of the heart, but rather cardiovascular disease, which refers to a group of disorders of the heart and blood vessels that lead to poor perfusion in various parts of the body. Cardiovascular disease is the most common cause of death in the United States. Poor blood flow in the blood vessels of the heart can lead to a heart attack, which in turn decreases how well the heart functions. Poor blood flow in the blood vessels of the brain can lead to strokes, which, depending on the location of the stroke, can have profound effects on brain function. Reducing cardiovascular risk factors which include high blood pressure, diabetes, high cholesterol, and obesity are therefore vital for everyone with or without PD.
The relationship between cardiovascular disease and PD was explored in a recent paper. Whether cardiovascular disease is even more common in PD than in the general population is not completely clear and warrants more investigation. There is some data that newly diagnosed people with PD may be at a small increased risk for heart attack and that a previous diagnosis of stroke is more prevalent in people with PD than in non-PD controls. Regardless, even if there is no direct link between cardiovascular disease and PD, reducing a person’s cardiovascular burden is good for brain health and keeping the brain as healthy as possible is good for someone with PD.
There may be a more specific relationship between diabetes, one of the key risk factors of cardiovascular disease, and PD, which we explored in a previous blog. A category of medications used for diabetes control is being studied for its effects on PD.
Imaging of the nervous system of the heart
Although not readily available, it is possible to image the sympathetic nervous system of the human heart by injecting a radioactive tracer, [123I]meta-iodo-benzyl-guanidine, (MIBG). Development of this technique, known as MIBG cardiac imaging, holds much promise as a test to confirm the diagnosis of PD (a state in which MIBG detection in the heart is diminished or absent), to identify those who are at risk of developing PD in the future, and to distinguish PD from related disorders. MIBG cardiac imaging is still considered an experimental procedure for detection of PD and is not yet in use as a clinical tool for this purpose.
Tips & Takeaways
- Lewy body pathology and neurodegeneration in both the brain and the autonomic nervous system can have early and profound effects on the cardiac system in people with PD.
- The most well-understood effect of this is neurogenic orthostatic hypotension (nOH) or drops in blood pressure upon standing.
- There are many lifestyle modifications as well as medications that can help with nOH, a very common non-motor symptom of PD. Be sure to talk to your doctor if you are experiencing dizziness, blurred vision, and/or fainting.
- Changes in heart rate, such as reduced heart rate variability, may possibly be an early non-motor symptom of Parkinson’s disease.
- Routine cardiologic care makes sense for patients with PD. A cardiologist can help manage nOH and ensure that the heart rhythm is normal. He or she can also screen for additional cardiologic problems that may be linked to PD