The brain-heart connection holds important lessons for clinicians

Have you ever stopped to think about how the brain and heart interact? The true extent of these interactions likely will remain opaque for some time. Nevertheless, scientists have made inroads in elucidating this important relationship.

From a physiologic perspective, the brain controls the heart via the sympathetic and parasympathetic components of the autonomic nervous system, both of which are affected by stress. Of course, many diseases and conditions are connected to stress. Learning more about the brain-heart connection, specifically it’s connections to stress, has clinical relevance for HCPs working to manage neurogenic and stress-related conditions, such as MI, atrial fibrillation, and heart failure.

A closer look

The cardiac autonomic nerves reflexively can change heart functions in response to baroreceptor, chemoreceptor, and nasopharyngeal activity. Central autonomic commands, such as those linked to physical activity, stress, sleep, and arousal, can also change cardiac function.

Neurodegenerative disorders can lead to progressive autonomic failure. On the other hand, autonomic hyperactivity can result from vascular, inflammatory, or traumatic lesions of the autonomic nervous systems, as well as adverse effects of drugs and chronic neurological disease. 

“Both acute and chronic manifestations of an imbalanced brain–heart interaction have a negative impact on health,” wrote the authors of a review article published in Philosophical Transactions of the Royal Society. “Simple, widely available and reliable cardiovascular markers of the sympathetic tone and of the sympathetic–parasympathetic balance are lacking. A deeper understanding of the connections between autonomic cardiac control and brain dynamics through advanced signal and neuroimage processing may lead to invaluable tools for the early detection and treatment of pathological changes in the brain–heart interaction.”

The authors suggested that heart rate variability (HRV) based on the electrocardiograph could be an impactful measure in detecting autonomic impairments and predicting the outcomes of neurological disorders.

This measure would be a cheap way to gauge sympathetic and parasympathetic tone and detect cardiovascular dysautonomia, the treatment of which can prevent the occurrence of potentially lethal paroxysmal or chronic autonomic hyperactivity. Historically, HRV has been used only to assess death risk after heart attack and to help diagnose cardiac autonomic neuropathy in those with diabetes. 

Stress and the heart

In a 2019 article published in Cerebrum, researchers noted that external stressors can impair heart activity. They cited, for instance, a classic study from the 1970s. Researchers asked volunteers to count to 100, then serially subtract 7s, creating a mental stress. While the volunteers were physically at rest, the test caused blood vessel constriction similar to a failed cardiac stress test.  

In other research, they noted that in more than 135,000 Swedish people, a history of stress-related disorders including PTSD heightened the chances of heart disease by more than 60% within one year of diagnosis.

From a pathophysiologic perspective, the rupture of an unstable plaque at the level of the coronary arteries during MI can trigger the sympathetic nervous system, leading to the release of adrenaline, which increases heart rate and blood pressure. These phenomena lead to the release of neuropeptide Y by platelets, which leads to spasm and occlusion of the coronary arteries.

Daily stress can moderate the risk of heart attack and stress, as well as hasten atherosclerosis. Factors that play a role include crosstalk among the central nervous system, heart, adrenal gland, and kidney, leading to the release of cortisol and heart-damaging neuropeptides. Other pathogenic effects of stress include the facilitation of inflammation, oxidative stress, and abnormal endothelial function.

Intriguingly, the amygdala may play a pivotal role in the prediction of heart disease. More specifically, the perigenual anterior cingulate cortex, which is a region that controls amygdala and reactions to psychosocial stress, may be implicated. 

As a panacea for stress, the researchers recommend various interventions including listening to music, relaxation techniques, and humor/comedy, as well as intranasal oxytocin, which has been shown to ameliorate parasympathetic tone and decrease chronic pain, which plays a role in stroke and heart disease.  

Neurogenic heart disease

In an intriguing hypothesis published in Neurology, a neurologist hypothesizes that because atrial fibrillation and heart failure are the most common sequelae pathology in that order, these conditions could both be neurogenic in nature. 

The author noted that atrial fibrillation is frequently caused by mental and psychological stress. Furthermore, researchers have identified genetic predisposition to stress-induced sudden cardiac death. Overall, 1%-2% of heart attacks could be neurogenic, with neurogenic cardiac disease under-recognized.

“Understanding more about brain-heart connections may lead to novel interventions for neurologic and cardiovascular conditions,” the author wrote. “The 'autonomic' nervous system is not autonomous.”

Sources

1. Boylan LS. Brain-heart Connection. Neurology.

2. Miller M. Emotional Rescue: The Heart-Brain Connection. Cerebrum.

3. Silvani A. Brain–heart interactions: physiology and clinical implications. Philosophical Transactions of the Royal Society.