Neurocardiology

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Neurocardiology is the study of the neurophysiological, neurological and neuroanatomical aspects of cardiology, including especially the neurological origins of cardiac disorders. [1] The effects of stress on the heart are studied in terms of the heart's interactions with both the peripheral nervous system and the central nervous system.

Contents

Clinical issues in neurocardiology include hypoxic–ischemic brain injury, neurogenic stress cardiomyopathy, cerebral embolism, encephalopathy, neurologic sequelae of cardiac and thoracic surgery and cardiac interventions, and cardiovascular findings in patients with primary neurological disease. [2]

Overview

Neurocardiology refers to the pathophysiological interplays of the nervous and cardiovascular systems. [3] The constant communication between the heart and the brain have proved invaluable to the interdisciplinary fields of neurological and cardiac diseases. [4]

The fundamental understanding of the communication between the heart and the brain via the nervous system has led scientists towards an understanding of its elaborate circuitry. The brain emits neurological signals of oscillating frequencies. The neural rhythms provide information on the steady-state conditions of healthy individuals. Variations in the neural rhythms provide evidence that a problem is present regarding physiologic regulation and help physicians to more quickly determine the underlying condition based on the given symptoms. [5]

The neurocardiac axis links the cardiovascular and nervous systems to physiological problems such as arrhythmias, epilepsy and stroke. These problems are related to the fundamental factor of stress on the body. As stated previously, the changes in neural oscillations can contribute to the knowledge of what a steady state in an individual looks like, especially because it changes based on the person, as well as contributing to the imbalance of the nervous system and physiological function. Moreover, the brain can control the heart rate through the sympathetic nervous system. [5]

Map between cardiovascular system and nervous system

The cardiovascular system is regulated by the autonomic nervous system, which includes the sympathetic and parasympathetic nervous systems. A distinct balance between these systems is crucial for the pathophysiology of cardiovascular disease. An imbalance can be caused by hormone levels, lifestyle, environmental stressors and injuries. [6]

The complicated link between the brain and the heart can be mapped out from the complex of higher nervous system influences descending down to the heart. This complex innervates key autonomic structures from the brain's cortex to the heart along the neurocardiac axis. The heart is both the source of life and a source of cardiac arrhythmias and complications. The information originates in the brain's cortex and descends down to the hypothalamus. The neural signals are then transferred to the brainstem, followed by the spinal cord—the location from which the heart receives all its signals. In further detail, the heart receives its neural input through parasympathetic and sympathetic ganglia and the lateral grey column of the spinal cord. [7]

Problems

The neurocardiac axis is the link to many problems regarding the physiological functions of the body. This includes cardiac ischemia, stroke, epilepsy, heart arrhythmias and cardiac myopathies. Many of these problems are due to the imbalance of the nervous system, resulting in symptoms that affect both the heart and the brain. [6]
The connection between the cardiovascular and nervous system has raised concerns in the training processes for medical students. Neurocardiology is based on an understanding that systems within the body are interconnected. When training within one specialty, doctors are more likely to associate patients' symptoms with their field. Without taking integration into account, doctors can consequently delay a correct diagnosis and treatment for the patient. [7] However, by specializing in a field, advancement in medicine continues as new findings come into perspective.[ citation needed ]

Stress

The physiological effects of stress on the body Stress 2.gif
The physiological effects of stress on the body

Cardiovascular systems are regulated by the autonomic nervous system, which includes the sympathetic and parasympathetic nervous systems. A distinct balance between these two systems is crucial for the pathophysiology of cardiovascular disease. Chronic stress has been widely studied for its effects on the body, resulting in an elevated heart rate (HR), reduced HR variability, elevated sympathetic tone and intensified cardiovascular activity. Consequently, stress promotes an autonomic imbalance in favor of the sympathetic nervous system. The activation of the sympathetic nervous system contributes to endothelial dysfunction, hypertension, atherosclerosis, insulin resistance and increased incidence of arrhythmias. [6] An imbalance in the autonomic nervous system has been documented in mood disorders; it is commonly regarded as a mediator between mood disorders and cardiovascular disorders.[ citation needed ]

The hypothalamus is the part of the brain that regulates function and responds to stress. When the brain perceives environmental danger, the amygdala fires a nerve impulse to the hypothalamus to initiate the body's fight-or-flight mode through the sympathetic nervous system. The stress response starts with the hypothalamus stimulating the pituitary gland, which releases the adrenocorticotropic hormone. This signals the release of cortisol, the stress hormone, initiating a multitude of physical effects on the body to aid in survival. A negative feedback loop is then needed to return the body to its resting state by signaling the parasympathetic nervous system. [8]

Prolonged stress leads to many hazards within the nervous system. Various hormones and glands become overworked, and chemical waste is produced, resulting in the degeneration of nerve cells. The result of prolonged stress is the breakdown of the body and the nervous system. Stress alone does not produce potentially deadly arrhythmias in normal healthy hearts; however, studies do appear to show that stress causes cardiac damage that may lead to arrhythmias.[ citation needed ]

Arrhythmias

In a study relating to the relationship between neurocardiology and arrhythmias and sudden cardiac death, the authors hypothesized that an individual with a diseased heart has a greater likelihood of experiencing cardiac arrhythmias and sudden cardiac death when the neurocardiac axis is activated. [7] An arrhythmia is defined as any disturbance in the cardiac activation sequence or any deviation from accepted limits for the rate or regularity of the normal impulse. The main types of arrhythmias leading to sudden cardiac death are tachyarrhythmias and bradyarrhythmia. Tachyarrhythmias are associated with ventricular fibrillation and ventricular tachycardia. Bradyarrhythmias are associated with complete atrioventricular blockage and sudden asystole. The underlying cause of sudden cardiac death is unclear, despite the understanding that heart disease causes arrhythmias, which in turn produce sudden cardiac death. [7] Lown describes the heart as the target, and the brain as the trigger. If a sudden cardiac death is triggered by an electrical accident, it can be treated with ventricular defibrillation. [9]

Stroke

Stroke activates the neurocardiac axis, producing arrhythmias, cardiac damage, and sudden death. In a recent study on patients with already diseased hearts and electrocardiographic abnormalities, there was evidence of lost hypothalamic–medullary integration at the midbrain. This resulted in the observation that overactivity in the parasympathetic nervous system may also cause sudden death with asystole after stroke. Catecholamine medications have been studied for their ability to mediate the effects of electrocardiographic changes and heart damage. [7]

Epilepsy

Sudden death from epilepsy is not very common, with a rate of approximately two cases in every thousand. The present understanding about how sudden cardiac death can result from epilepsy is that the brain stimulates an arrhythmia. Recordings during seizures report that the onset of tachycardia just prior to the seizure is common, with both atrial and ventricular ectopy. [7] A sudden epileptic death may be a result of the sympathetic activation or autonomic imbalance of the nervous system, as described earlier.[ citation needed ]

Emotions

The relationship between emotions and their effect on the destabilization of the heart continues to be a mystery. It is considered that both the spatial and temporal patterns of autonomic input to the heart play a key role in altered electrophysiological parameters. The body continually attempts to maintain homeostasis through the baroreflex. This balance in the autonomic neural input to the heart in response to the pressure and volume changes leads to alterations in the baroreceptors. [10]

Treatments

Medications

Drugs with both antidepressant and cardiometabolic actions are in the process of being studied. Most medications work on stressors of the heart and some also work to treat neuropsychiatric diseases. Antidepressant medications have shown to be insufficient to induce the normalization of cardiovascular dysfunctions, which are associated with psychiatric conditions. [11]

Physical activity and diet

Lifestyle modifications play a crucial role in the management of cardiovascular and neurological diseases. Physical activity and a well-balanced diet favor cardiovascular conditioning and improve performance and capacity. Exercise has a positive effect on the metabolism, which controls glucose levels, especially for stress-related pathology and brain disorders such as depression, which impose a heavy burden on the cardiovascular system. Many studies are currently being conducted to gather more information regarding the common mediators of cardiovascular disease and the central nervous system. The brain–heart interaction is considered bidirectional; however, the central nervous system is often regulated more strongly than the heart and blood vessels. [6]

See also

Related Research Articles

<span class="mw-page-title-main">Autonomic nervous system</span> Division of the nervous system supplying internal organs, smooth muscle and glands

The autonomic nervous system (ANS), sometimes called the visceral nervous system and formerly the vegetative nervous system, is a division of the nervous system that operates internal organs, smooth muscle and glands. The autonomic nervous system is a control system that acts largely unconsciously and regulates bodily functions, such as the heart rate, its force of contraction, digestion, respiratory rate, pupillary response, urination, and sexual arousal. This system is the primary mechanism in control of the fight-or-flight response.

<span class="mw-page-title-main">Sympathetic nervous system</span> Part of the autonomic nervous system which stimulates fight-or-flight responses

The sympathetic nervous system is one of the three divisions of the autonomic nervous system, the others being the parasympathetic nervous system and the enteric nervous system. The enteric nervous system is sometimes considered part of the autonomic nervous system, and sometimes considered an independent system.

<span class="mw-page-title-main">Heart rate</span> Speed of the heartbeat, measured in beats per minute

Heart rate is the frequency of the heartbeat measured by the number of contractions of the heart per minute. The heart rate varies according to the body's physical needs, including the need to absorb oxygen and excrete carbon dioxide. It is also modulated by numerous factors, including genetics, physical fitness, stress or psychological status, diet, drugs, hormonal status, environment, and disease/illness, as well as the interaction between these factors. It is usually equal or close to the pulse rate measured at any peripheral point.

<span class="mw-page-title-main">Dysautonomia</span> Any disease or malfunction of the autonomic nervous system

Dysautonomia, autonomic failure, or autonomic dysfunction is a condition in which the autonomic nervous system (ANS) does not work properly. This may affect the functioning of the heart, bladder, intestines, sweat glands, pupils, and blood vessels. Dysautonomia has many causes, not all of which may be classified as neuropathic. A number of conditions can feature dysautonomia, such as Parkinson's disease, multiple system atrophy, dementia with Lewy bodies, Ehlers–Danlos syndromes, autoimmune autonomic ganglionopathy and autonomic neuropathy, HIV/AIDS, mitochondrial cytopathy, pure autonomic failure, autism, and postural orthostatic tachycardia syndrome.

<span class="mw-page-title-main">Palpitations</span> Perceived cardiac abnormality in which ones heartbeat can be felt

Palpitations are perceived abnormalities of the heartbeat characterized by awareness of cardiac muscle contractions in the chest, which is further characterized by the hard, fast and/or irregular beatings of the heart.

The cardiovascular centre is a part of the human brain which regulates heart rate through the nervous and endocrine systems. It is considered one of the vital centres of the medulla oblongata.

<span class="mw-page-title-main">Baroreflex</span> Homeostatic mechanism in the body

The baroreflex or baroreceptor reflex is one of the body's homeostatic mechanisms that helps to maintain blood pressure at nearly constant levels. The baroreflex provides a rapid negative feedback loop in which an elevated blood pressure causes the heart rate to decrease. Decreased blood pressure decreases baroreflex activation and causes heart rate to increase and to restore blood pressure levels. Their function is to sense pressure changes by responding to change in the tension of the arterial wall. The baroreflex can begin to act in less than the duration of a cardiac cycle and thus baroreflex adjustments are key factors in dealing with postural hypotension, the tendency for blood pressure to decrease on standing due to gravity.

Acute stress reaction and acute stress disorder (ASD) is a psychological response to a terrifying, traumatic or surprising experience. Combat stress reaction (CSR) is a similar response to the trauma of war. The reactions may include but are not limited to intrusive or dissociative symptoms, and reactivity symptoms such as avoidance or arousal. It may be exhibited for days or weeks after the traumatic event. If the condition is not correctly addressed, it may develop into post-traumatic stress disorder (PTSD).

<span class="mw-page-title-main">Heart rate variability</span> Variation in the time intervals between heartbeats

Heart rate variability (HRV) is the physiological phenomenon of variation in the time interval between heartbeats. It is measured by the variation in the beat-to-beat interval.

Heart rate turbulence (HRT) is a baroreflex-mediated adjustment of heart rate which acts as a counter-mechanism to premature ventricular contraction (PVC). It consists of a brief speed-up in heart rate, followed by a slow decrease back to the baseline rate. PVCs can occur naturally in most otherwise-healthy adults, so measuring the characteristics of a given person's HRT can offer a non-invasive way to evaluate certain aspects of their cardiac or autonomic function without applying artificial external stimuli.

Neuroimmunology is a field combining neuroscience, the study of the nervous system, and immunology, the study of the immune system. Neuroimmunologists seek to better understand the interactions of these two complex systems during development, homeostasis, and response to injuries. A long-term goal of this rapidly developing research area is to further develop our understanding of the pathology of certain neurological diseases, some of which have no clear etiology. In doing so, neuroimmunology contributes to development of new pharmacological treatments for several neurological conditions. Many types of interactions involve both the nervous and immune systems including the physiological functioning of the two systems in health and disease, malfunction of either and or both systems that leads to disorders, and the physical, chemical, and environmental stressors that affect the two systems on a daily basis.

<span class="mw-page-title-main">Lateral grey column</span> One of three columns of grey matter in the spinal cord

The lateral grey column is one of the three grey columns of the spinal cord ; the others being the anterior and posterior grey columns. The lateral grey column is primarily involved with activity in the sympathetic division of the autonomic motor system. It projects to the side as a triangular field in the thoracic and upper lumbar regions of the postero-lateral part of the anterior grey column.

Vagal tone is activity of the vagus nerve and a fundamental component of the parasympathetic branch of the autonomic nervous system. This branch of the nervous system is not under conscious control and is largely responsible for the regulation of several body compartments at rest. Vagal activity results in various effects, including: heart rate reduction, vasodilation/constriction of vessels, glandular activity in the heart, lungs, and digestive tract, liver, immune system regulation as well as control of gastrointestinal sensitivity, motility and inflammation.

<span class="mw-page-title-main">Polyvagal theory</span> Proposed constructs pertaining to the vagus nerve

Polyvagal theory (PVT) is a collection of proposed evolutionary, neuroscientific, and psychological constructs pertaining to the role of the vagus nerve in emotion regulation, social connection and fear response. The theory was introduced in 1994 by Stephen Porges. There is consensus among experts that the assumptions of the polyvagal theory are untenable. PVT is popular among some clinical practitioners and patients, but it is not endorsed by current social neuroscience.

<span class="mw-page-title-main">Syncope (medicine)</span> Transient loss of consciousness and postural tone

Syncope, commonly known as fainting or passing out, is a loss of consciousness and muscle strength characterized by a fast onset, short duration, and spontaneous recovery. It is caused by a decrease in blood flow to the brain, typically from low blood pressure. There are sometimes symptoms before the loss of consciousness such as lightheadedness, sweating, pale skin, blurred vision, nausea, vomiting, or feeling warm. Syncope may also be associated with a short episode of muscle twitching. Psychiatric causes can also be determined when a patient experiences fear, anxiety, or panic; particularly before a stressful event, usually medical in nature. When consciousness and muscle strength are not completely lost, it is called presyncope. It is recommended that presyncope be treated the same as syncope.

<span class="mw-page-title-main">Arrhythmia</span> Group of medical conditions characterized by irregular heartbeat

Arrhythmias, also known as cardiac arrhythmias, are irregularities in the heartbeat, including when it is too fast or too slow. A resting heart rate that is too fast – above 100 beats per minute in adults – is called tachycardia, and a resting heart rate that is too slow – below 60 beats per minute – is called bradycardia. Some types of arrhythmias have no symptoms. Symptoms, when present, may include palpitations or feeling a pause between heartbeats. In more serious cases, there may be lightheadedness, passing out, shortness of breath, chest pain, or decreased level of consciousness. While most cases of arrhythmia are not serious, some predispose a person to complications such as stroke or heart failure. Others may result in sudden death.

Orthostatic syncope refers to syncope resulting from a postural decrease in blood pressure, termed orthostatic hypotension.

Vagotonia is the state of the autonomic nervous system in which there is increased parasympathetic input through the vagus nerve, or the equilibrium between the sympathetic and parasympathetic is biased towards the latter. The opposite phenomenon has been referred to as sympatheticotonia.

<span class="mw-page-title-main">Sympathoadrenal system</span>

The sympathoadrenal system is a physiological connection between the sympathetic nervous system and the adrenal medulla and is crucial in an organism's physiological response to outside stimuli. When the body receives sensory information, the sympathetic nervous system sends a signal to preganglionic nerve fibers, which activate the adrenal medulla through acetylcholine. Once activated, norepinephrine and epinephrine are released directly into the blood by adrenomedullary cells where they act as the bodily mechanism for "fight-or-flight" responses. Because of this, the sympathoadrenal system plays a large role in maintaining glucose levels, sodium levels, blood pressure, and various other metabolic pathways that couple with bodily responses to the environment. During numerous diseased states, such as hypoglycemia or even stress, the body's metabolic processes are skewed. The sympathoadrenal system works to return the body to homeostasis through the activation or inactivation of the adrenal gland. However, more severe disorders of the sympathoadrenal system such as pheochromocytoma can affect the body's ability to maintain a homeostatic state. In these cases, curative agents such as adrenergic agonists and antagonists are used to modify epinephrine and norepinephrine levels released by the adrenal medulla.

Autonomic drugs are substances that can either inhibit or enhance the functions of the parasympathetic and sympathetic nervous systems. This type of drug can be used to treat a wide range of diseases an disorders, including glaucoma, asthma, and disorders of the urinary, gastrointestinal and circulatory systems.

References

  1. ↑ Natelson BH (Feb 1985). "Neurocardiology. An interdisciplinary area for the 80s". Arch. Neurol. 42 (2): 178–84. doi:10.1001/archneur.1985.04060020096022. PMID   3883960.
  2. ↑ Louis R Caplan; J Willis Hurst; Marc I Chimowitz (1999). Clinical neurocardiology. Vol. 26. p. 324. doi:10.1201/b14098. ISBN   9780429074516. PMC   325678 .{{cite book}}: |journal= ignored (help)
  3. ↑ van der Wall, E; W.H. van Gilst (December 2012). "Neurocardiology: close interaction between heart and brain". Netherlands Heart Journal. 21 (2): 51–52. doi:10.1007/s12471-012-0369-4. PMC   3547430 . PMID   23239452.
  4. ↑ Carrero, Milton (12 February 2011). "One Vital Organ: Heart is More than a Pump". The Morning Call.
  5. 1 2 Fallen, Ernest (December 2000). "Hidden rhythms in the heart record: a primer on neurocardiology". Clin Invest Med. 23 (6): 387–394. PMID   11152408.
  6. 1 2 3 4 5 6 7 Pereira, VH; Cerqueira, JJ; Palha, JA; Sousa, N (5 June 2013). "Stressed brain, diseased heart: a review on the pathophysiologic mechanisms of neurocardiology". International Journal of Cardiology. 166 (1): 30–37. doi:10.1016/j.ijcard.2012.03.165. hdl: 1822/24143 . PMID   22521375.
  7. 1 2 3 4 5 6 Davis, Alan (1993). "Brain-Heart Interactions: The Neurocardiology of Arrhythmia and Sudden Cardiac Death". Texas Heart Institute Journal. 20 (3): 158–169. PMC   325088 . PMID   8219819.
  8. ↑ "How Your nervous System Gets Out of Sync" (PDF). Retrieved 28 October 2013.
  9. ↑ Lown, B; Verrier RL; Rabinowitz SH (May 1977). "Neural and Psychologic Mechanisms and the Problem of Sudden Cardiac Death". American Journal of Cardiology. 39 (6): 890–902. doi:10.1016/s0002-9149(77)80044-1. PMID   860697.
  10. ↑ Taggart, Peter; Mark Boyett; Sunil Logantha; Pier Lambiase (October 2011). "Anger, Emotion, and Arrhythmias: from Brain to Heart". Frontiers in Physiology. 2: 67. doi: 10.3389/fphys.2011.00067 . PMC   3196868 . PMID   22022314.
  11. 1 2 3 Goldstein, David S. (2012). "Neurocardiology: Therapeutic Implications for Cardiovascular Disease". Cardiovascular Therapeutics. 30 (2): 89–106. doi:10.1111/j.1755-5922.2010.00244.x. PMC   4893308 . PMID   21108771.
  12. ↑ Maron, Bradley (2010). "Aldosterone Receptor Antagonists: Effective but Often Forgotten". Circulation. 121 (7): 934–939. doi:10.1161/CIRCULATIONAHA.109.895235. PMC   2828634 . PMID   20177008.

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