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 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 into understanding its elaborate circuitry. The brain emits neurological signals of oscillating frequencies. The neural rhythms provide information on steady state conditions of healthy individuals. Variations in the neural rhythms provide evidence that a problem is present regarding physiologic regulation and help physicians determine the underlying condition quicker 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 to 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, which is the location where the heart receives all its signals from. In further detail, the heart receives its neural input through parasympathetic and sympathetic ganglia and 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, and most importantly, 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 brought up a concern in the training processes for medical students. Neurocardiology is the understanding that the body is interconnected and weave in and out of other systems. When training within one specialty, the doctors are more likely to associate patients' symptoms to their field. Without taking the integration into account, the doctor 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 systems, 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 on its effects of 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. The 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, chemical waste is produced resulting in 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 relationship of neurocardiology of arrhythmias and sudden cardiac death, they hypothesized that the 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 of rate or regularity of the normal impulse. The main types of arrhythmia leading to sudden cardiac death are tachyarrhythmias and bradyarrhythmias. 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 is called the trigger. Sudden cardiac death is triggered by an electrical accident, which 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 fact that overactivity in the parasympathetic nervous system may also cause sudden death with asystole after stroke. Catecholamine medications have been studied 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 2 in a thousand. The present understanding about how sudden cardiac death can result from epilepsy is that the brain is stimulating 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] The 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 of the medications work on stressors of the heart and some also work to treat the neuropsychiatric diseases. Antidepressant medications have shown to be insufficient to induce normalization of the cardiovascular dysfunctions, which are associated with the psychiatric conditions. [11]

Physical activity and diet

Lifestyle modifications play a crucial role in management of cardiovascular and neurological diseases. Physical activity and a well-balanced diet favor cardiovascular conditioning and improves 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 done for more information and knowledge regarding the common mediators for cardiovascular disease and the central nervous system. The brain-heart interaction is considered bidirectional, however the majority of times the central nervous system is regulated more over the heart and blood vessels. [6]

See also

Related Research Articles

<span class="mw-page-title-main">Sympathetic nervous system</span> Division of the autonomic nervous system

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.

Heart rate is the speed of the heartbeat measured by the number of contractions (beats) of the heart per minute (bpm). The heart rate can vary according to the body's physical needs, including the need to absorb oxygen and excrete carbon dioxide, but is also modulated by numerous factors, including, but not limited to, genetics, physical fitness, stress or psychological status, diet, drugs, hormonal status, environment, and disease/illness as well as the interaction between and among these factors. It is usually equal or close to the pulse measured at any peripheral point.

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

Dysautonomia 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, autonomic failure, 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.

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 disorder is a psychological response to a terrifying, traumatic or surprising experience. It may bring about delayed stress reactions if not correctly addressed.

<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 the return to equilibrium of heart rate after a premature ventricular contraction (PVC). It consists of a brief speed-up in heart rate, followed by a slow decrease back to the baseline rate. An important feature of HRT is that PVCs occur naturally in most adults, so measuring the characteristics of a given person's HRT offers a non-invasive way to evaluate his or her cardiac function without applying artificial external stimuli.

Lateral grey column

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.

<span class="mw-page-title-main">Catecholaminergic polymorphic ventricular tachycardia</span> Medical condition

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is an inherited genetic disorder that predisposes those affected to potentially life-threatening abnormal heart rhythms or arrhythmias. The arrhythmias seen in CPVT typically occur during exercise or at times of emotional stress, and classically take the form of bidirectional ventricular tachycardia or ventricular fibrillation. Those affected may be asymptomatic, but they may also experience blackouts or even sudden cardiac death.

Vagal tone is activity of the vagus nerve, the 10th cranial 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.

Polyvagal theory Unproven constructs pertaining to the vagus nerve

Polyvagal theory is a collection of unproven, evolutionary, neuroscientific, and psychological constructs pertaining to the role of the vagus nerve in emotion regulation, social connection and fear response, introduced in 1994 by Stephen Porges.

Syncope (medicine) 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.

Neural top–down control of physiology concerns the direct regulation by the brain of physiological functions. Cellular functions include the immune system’s production of T-lymphocytes and antibodies, and nonimmune related homeostatic functions such as liver gluconeogenesis, sodium reabsorption, osmoregulation, and brown adipose tissue nonshivering thermogenesis. This regulation occurs through the sympathetic and parasympathetic system, and their direct innervation of body organs and tissues that starts in the brainstem. There is also a noninnervation hormonal control through the hypothalamus and pituitary (HPA). These lower brain areas are under control of cerebral cortex ones. Such cortical regulation differs between its left and right sides. Pavlovian conditioning shows that brain control over basic cell level physiological function can be learned.

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

Arrhythmias, also known as cardiac arrhythmias, heart arrhythmias, or dysrhythmias, 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 or chest pain. 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.

Heart rhythm disturbances have been seen among astronauts. Most of these have been related to cardiovascular disease, but it is not clear whether this was due to pre-existing conditions or effects of space flight. It is hoped that advanced screening for coronary disease has greatly mitigated this risk. Other heart rhythm problems, such as atrial fibrillation, can develop over time, necessitating periodic screening of crewmembers’ heart rhythms. Beyond these terrestrial heart risks, some concern exists that prolonged exposure to microgravity may lead to heart rhythm disturbances. Although this has not been observed to date, further surveillance is warranted.

George Edward Billman is an American physiologist and professor at Ohio State University. After receiving a Ph.D from the University of Kentucky in 1980, Billman began his professional career at the University of Oklahoma. In 1984, he joined the Ohio State staff, where he became an associate professor in 1990 and a full professor in 1996.

Autonomic drugs 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, such as glaucoma, asthma, urinary, gastrointestinal and cardiopulmonary disorders.

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. Texas Heart Institute Journal. Vol. 26. p. 324. doi:10.1201/b14098. ISBN   9780429074516. PMC   325678 .
  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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