The heart as a sensory organ

Interoceptive signals from the heart and coronary circulation in health and disease

This review considers interoceptive signalling from the heart and coronary circulation. Vagal and cardiac sympathetic afferent sensory nerve endings are distributed throughout the atria, ventricles (mainly left), and coronary artery. A small proportion of cardiac receptors attached to thick myelinated vagal afferents are tonically active during the cardiac cycle. Dependent upon location, these mechanoreceptors detect fluctuations in atrial volume and coronary arterial perfusion. Atrial volume and coronary arterial signals contribute to beat-to-beat feedback control and physiological homeostasis. Most cardiac receptors are attached to thinly myelinated or nonmyelinated C fibres, many of which are unresponsive to the cardiac cycle. Of these, there are many chemically sensitive cardiac receptors which are activated during myocardial stress by locally released endogenous substances. In contrast, some tonically inactive receptors become activated by irregular ventricular wall mechanics or by distortion of the ischaemic myocardium. Furthermore, some are excited both by chemical mediators of ischaemia and wall abnormalities. Reflex responses arising from cardiac receptors attached to thinly myelinated or nonmyelinated are complex. Impulses that project centrally through vagal afferents elicit sympathoinhibition and hypotension, whereas impulses travelling in cardiac sympathetic afferents and spinal pathways elicit sympathoexcitation and hypertension. Two opposing cardiac reflexes may provide a mechanism for fine-tuning a composite haemodynamic response during myocardial stress. Sympathetic afferents provide the primary pathway for transmission of cardiac nociception to the central nervous system. However, activation of sympathetic afferents may increase susceptibility to life-threatening arrhythmias. Notably, the cardiac sympathetic afferent reflex predominates in pathophysiological states including hypertension and heart failure.

Does stroke volume influence heartbeat evoked responses?

We know surprisingly little on how heartbeat-evoked responses (HERs) vary with cardiac parameters. Here, we measured both stroke volume, or volume of blood ejected at each heartbeat, with impedance cardiography, and HER amplitude with magneto-encephalography, in 21 male and female participants at rest with eyes open. We observed that HER co-fluctuates with stroke volume on a beat-to-beat basis, but only when no correction for cardiac artifact was performed. This highlights the importance of an ICA correction tailored to the cardiac artifact. We also observed that easy-to-measure cardiac parameters (interbeat intervals, ECG amplitude) are sensitive to stroke volume fluctuations and can be used as proxies when stroke volume measurements are not available. Finally, interindividual differences in stroke volume were reflected in MEG data, but whether this effect is locked to heartbeats is unclear. Altogether, our results question assumptions on the link between stroke volume and HERs.

Acute myocardial infarction not attributed to coronary artery disease: A seldom initial presentation of a left ventricular myxoma

Although myxoma represents the most frequent non-malignant cardiac primary tumor; it is extremely rare met in the left ventricle. Clinical features of the neoplasm extend from symptomless to critical signs of either ischemia or embolism. We describe here an unusual case of a huge left ventricular myxoma in a 68-year-old man, presented with clinical and ECG findings of an inferior wall myocardial infarction. The patient was primarily referred to our institution for coronary angiography, which showed no coronary artery disease. Further examinations revealed a left ventricular mass as the possible source of embolization, thus the patient underwent surgery for tumor excision. The postoperative course was unremarkable. A bibliographical analysis demonstrated that those tumors are rare but treatable causes of embolic myocardial infarction, thus profound clinical intuition, proper utilization of imaging modalities, administration of anticoagulants preoperatively, as well immediate surgical removal are justified.

Cough as a Cause and Consequence of Heart Dysfunction - Current State of Art

The cough reflex is an airway defensive process that can be modulated by afferent inputs from organs located also out of the respiratory system. A bidirectional relationship between cough and heart dysfunctions are presented in the article, with the special insights into an arrhythmia-triggered cough. Albeit rare, cough induced by cardiac pathologies (mainly arrhythmias) seems to be an interesting and underestimated phenomenon. This condition is usually associated with the presence of abnormal heart rhythms and ceases with successful treatment of arrhythmia either by pharmacotherapy or by radiofrequency ablation of arrhythmogenic substrate. The two main hypotheses on cough-heart relationships - reflex and hemodynamic - are discussed in the review, including the authors' perspective based on the experiences with an arrhythmia-triggered cough.

Cardiac Dysfunction in Neurocritical Care: An Autonomic Perspective

A number of neurologic disorders can cause cardiac dysfunction by involving the conductive system and contractile apparatus of the heart. This is especially prominent in the neurocritical care setting where the spectrum of cardiac dysfunction due to acute neurologic injury ranges from trivial and isolated electrocardiographic changes to malignant arrhythmias and sudden death (Table 1). The mechanism of these cardiac complications is complex and not fully understood. An understanding of the neuroanatomical structures and pathways is of immense importance to comprehend the underlying pathophysiology that culminates as cardiac damage and dysregulation. Once the process is initiated, it can complicate and adversely affect the outcome of primary neurologic conditions commonly seen in the neurocritical care setting. Not only are these cardiac disorders under-recognized, there is a paucity of data to formulate evidence-based guidelines regarding early detection, acute management, and preventive strategies. However, certain details of clinical features and their course combined with location of primary neurologic lesion on neuroimaging and data obtained from laboratory investigations can be of great value to develop a strategy to appropriately manage these patients and to prevent adverse outcome from these cardiac complications. In this review, we highlight the mechanisms of cardiac dysfunction due to catastrophic neurologic conditions or due to stress of critical illness. We also address various clinical syndromes of cardiac dysfunction that occur as a result of the neurologic illness and in turn may complicate the course of the primary neurologic condition.

The neural monitoring of visceral inputs, rather than attention, accounts for first-person perspective in conscious vision

Why should a scientist whose aim is to unravel the neural mechanisms of perception consider brain-body interactions seriously? Brain-body interactions have traditionally been associated with emotion, effort, or stress, but not with the "cold" processes of perception and attention. Here, we review recent experimental evidence suggesting a different picture: the neural monitoring of bodily state, and in particular the neural monitoring of the heart, affects visual perception. The impact of spontaneous fluctuations of neural responses to heartbeats on visual detection is as large as the impact of explicit manipulations of spatial attention in perceptual tasks. However, we propose that the neural monitoring of visceral inputs plays a specific role in conscious perception, distinct from the role of attention. The neural monitoring of organs such as the heart or the gut would generate a subject-centered reference frame, from which the first-person perspective inherent to conscious perception can develop. In this view, conscious perception results from the integration of visual content with first-person perspective.

Wellens Syndrome with Syncope but Not Chest Pain

We report the case of a woman in her 70s presenting to the emergency department with syncope, troponemia, and an electrocardiogram with deep symmetric T-wave inversions in V2 and V3 and prolonged QTc. Her presentation was concerning for acute coronary syndrome, Wellens syndrome in particular, given the elevated troponin levels, lack of ST segment changes, and characteristic T-wave findings. The diagnosis was confirmed with angiography that showed a critical left anterior descending (LAD) artery occlusion. Since myocardial infarction does not typically present with syncope, we explored the differential diagnoses for T-wave inversions, which include electrolyte abnormalities, medications, intracranial hemorrhage, pulmonary embolism, and other cardiac diseases that were ruled out in our patient. We also explored the pathophysiology leading to syncope in the setting of acute myocardial infarction including arrhythmias and exaggerated neurally mediated response. Our patient received two drug-eluting stents to the LAD artery and was started on dual antiplatelet therapy, beta-blockers, and an angiotensin-converting enzyme inhibitor.

Paradoxical muscle sympathetic reflex activation in human heart failure

BACKGROUND

Muscle sympathetic activation in heart failure with reduced ejection fraction (HFrEF) has been attributed, on the basis of multiunit recordings, to attenuated inhibitory feedback from stretch-sensitive cardiopulmonary mechanoreceptors. However, such preparations integrate 2 populations of single units exhibiting directionally opposite firing when atrial pressure is perturbed. We tested the hypothesis that the proportion of single units firing paradoxically when filling pressure increases is augmented in HFrEF.

METHODS AND RESULTS

Muscle sympathetic nerve activity and estimated central venous pressure were recorded during nonhypotensive lower body negative pressure (LBNP; -10 mm Hg) and nonhypertensive positive pressure (LBPP; +10 mm Hg) in 11 treated HFrEF (left ventricular ejection fraction 25 ± 6% [mean ± standard deviation]) patients and 14 similarly aged controls. Single-unit muscle sympathetic nerve activity discharge was termed either anticipated, if firing frequency exhibited classic negative-feedback responses, or paradoxical. LBNP and LBPP had no heart rate, stroke volume, or blood pressure effects (P>0.05). Estimated central venous pressure decreased with LBNP (P<0.05), increased with LBPP (P<0.05), and was consistently higher in HFrEF (P<0.05). During LBNP, the ratio of single units with anticipated and paradoxical discharge was similar in HFrEF (18:7) and controls (27:5), whereas LBPP elicited paradoxical reflex excitation in a greater proportion of HFrEF single units (7:18 versus 24:6; P=0.0001). Consequently, LBPP increased mean single-unit firing frequency (P<0.05) and did not inhibit multiunit muscle sympathetic nerve activity of HFrEF subjects (P<0.05 versus controls). Firing of 12/18 HFrEF (but no control) single units increased during both LBPP and LBNP.

CONCLUSION

These findings provide the first evidence in human HFrEF for an augmented excitatory cardiopulmonary-muscle sympathetic nerve activity reflex response to increased preload, incorporating 2 distinct single-unit populations with differing firing properties.

Microneurographic evidence in healthy middle-aged humans for a sympathoexcitatory reflex activated by atrial pressure

Atrial mechanoreceptors, stimulated by increased pressure or volume, elicit in healthy humans a net sympathoinhibitory response. The co-existence of an atrial reflex eliciting muscle sympathoexcitation has been postulated but undetected by conventional multi-unit muscle sympathetic nerve activity (MSNA). We hypothesized that in response to a selective increase in atrial pressure, single-unit MSNA would reveal a subpopulation of efferent sympathetic neurons with firing patterns opposite to the integrated multi-unit MSNA envelope. Multi- and single-unit MSNA recordings were acquired in eight healthy middle-aged subjects (age, 57 ± 8 years; body mass index, 25 ± 2 kg/m2) submitted to selective decreases or increases in atrial pressure by nonhypotensive lower body negative pressure (LBNP; −10 mmHg) or nonhypertensive lower body positive pressure (LBPP; +10 mmHg), respectively. Single-unit MSNA firing responses were classified as anticipated if spike frequency and incidence increased with LBNP or decreased with LBPP and paradoxical if they decreased with LBNP or increased with LBPP. LBNP decreased (3.2 ± 2.8 to 1.4 ± 3.1 mmHg, P < 0.01) and LBPP increased (3.3 ± 2.7 to 4.9 ± 2.8 mmHg, P < 0.01) estimated central venous pressure without affecting stroke volume, systemic pressure, or resistance. Multi-unit MSNA increased with LBNP (31 ± 17 to 38 ± 19 bursts/min, P < 0.01) and diminished with LBPP (33 ± 15 to 28 ± 15 bursts/min, P < 0.01). Of 21 single-units identified, 76% exhibited firing responses to both LBNP and LBPP concordant with multi-unit MSNA, whereas 24% demonstrated discordant or paradoxical responses. The detection of two subpopulations of single-units within the multi-unit MSNA recording, exhibiting opposite firing characteristics, establishes the first evidence in humans for the existence of an excitatory cardiac-muscle sympathetic reflex activated by increasing atrial pressure.

The mechanism of the negative chronotropic and dromotropic actions of adenosine 5'-triphosphate in the heart: an update

Adenosine 5'-triphosphate (ATP) plays a critical role in intracellular metabolism and energetics. Extracellular ATP is rapidly degraded to adenosine by ectoenzymes. Both ATP and adenosine suppress cardiac pacemakers' automaticity and atrioventricular nodal conduction, albeit via the different mechanism of actions. This historical update summarizes the current knowledge regarding the negative chronotropic and dromotropic actions of ATP and discusses the clinical implications regarding the utility of ATP as a diagnostic and therapeutic agent in the management of neutrally mediated syncope and paroxysmal supra ventricular tachycardia.

Torsades de pointes arrhythmia in a patient with left ventricular myxoma

A 38-year-old woman suffered from syncopes due to torsades de pointes arrhythmias. Echocardiography showed a left ventricular mass that was resected. By immunohistochemical investigations, an organized thrombus was excluded and the diagnosis of a rare ventricular myxoma was confirmed. Postoperatively the arrhythmias resolved without recurrence. We conclude that left ventricular myxoma may cause life-threatening arrhythmias, possibly by irritation of cardiac mechanoreceptors. To our knowledge, this is the first case of a left ventricular myxoma associated with a torsades de pointes arrhythmia.

Systemic neurohumoral activation and vasoconstriction during pacing-induced acute myocardial ischemia in patients with stable angina pectoris

To identify the effect of myocardial ischemia on systemic neurohormones and vascular resistance, 32 untreated, normotensive patients with coronary artery disease underwent incremental atrial pacing until angina. Arterial and coronary venous lactate and arterial values of catecholamines and angiotensin II were determined at control, at maximal pacing rates, and at 1, 2, 5 and 30 minutes after pacing. Based on pacing-induced ST-segment depression (greater than or equal to 0.1 mV) or myocardial lactate production, or both, patients were selected as ischemic (n = 25) or nonischemic (n = 7). Baseline clinical and hemodynamic data were comparable. During pacing, chest pain was similar (20 ischemic vs 7 nonischemic patients). Also, hemodynamic measurements were comparable, except for contractility, which did not improve, and left ventricular end-diastolic pressure, which significantly increased in ischemic patients. Moreover, during ischemia arterial pressures increased significantly (13%) and systemic resistance increased from 1,470 +/- 60 (control) to 1,632 +/- 76 dynes.s.cm-5 5 minutes after pacing (p less than 0.05) in ischemic but not in nonischemic patients. Pacing did not affect neurohormones in nonischemic patients. In contrast, norepinephrine in ischemic patients increased significantly from 1.7 +/- 0.2 (control) to 2.6 +/- 0.3 (maximal pacing) and to 3.0 +/- 0.4 nmol/liter (1 minute after pacing), whereas angiotensin II levels increased from 6.2 +/- 1.4 (control) to 9.3 +/- 2.1 pmol/liter (1 minute after pacing, p less than 0.05). Epinephrine only increased during maximal rates (0.9 +/- 0.1 vs 0.6 +/- 0.1 nmol/liter at control, p less than 0.05). Thus, myocardial ischemia activates circulating catecholamines and angiotensin II, accompanied by systemic vasoconstriction.(ABSTRACT TRUNCATED AT 250 WORDS)

Anatomical, physiological, and theoretical basis for the antiepileptic effect of vagus nerve stimulation

The vagus is a mixed nerve carrying somatic and visceral afferents and efferents. The majority of vagal nerve fibers are visceral afferents and have a wide distribution throughout the central nervous system (CNS) either monosynaptically or via the nucleus of the solitary tract. Besides activation of well-defined reflexes, vagal stimulation produces evoked potentials recorded from the cerebral cortex, the hippocampus, the thalamus, and the cerebellum. Activation of vagal afferents can depress monosynaptic reflexes, decrease the activity of spinothalamic neurons, and increase pain threshold. Depending on the stimulation parameters, vagal afferent stimulation in experimental animals can produce electroencephalographic (EEG) synchronization or desynchronization and has been shown to affect sleep states. The desychronization of the EEG appears to depend on activation of afferent fibers that have conduction velocities of less than or equal to 15 m/s. Vagal afferent stimulation can also influence the activity of interictal cortical spikes produced by topical strychnine application, and either attenuate or stop seizures produced by pentylenetetrazol, 3-mercaptoproprionic acid, maximal electroshock, and topical alumina gel. The mechanisms for the antiepileptic effects of vagal stimulation are not fully understood but probably relate to effects on the reticular activating system. The vagus provides an easily accessible, peripheral route to modulate CNS function.

Calcitonin gene-related peptide: release by capsaicin and prolongation of the action potential in the guinea-pig heart

The mechanisms underlying the stimulatory effects of capsaicin on the contractility of the guinea-pig heart were studied in vitro. Capsaicin (10(-7) to 10(-5) M) caused an increased overflow of immunoreactive material, suggesting release of calcitonin gene-related peptide (CGRP)-and neurokinin A (NKA)-like immunoreactivity (-LI), but not of neuropeptide Y (NPY)-LI from the isolated Langendorff-perfused whole heart. The capsaicin-induced release was calcium-dependent. During exposure to capsaicin, the heart rate was increased, while the contractile force was reduced. In addition to releasing CGRP and NKA-LI, potassium (60 mM) also increased the overflow of NPY-LI. The potassium-induced release of peptides was less calcium-dependent than the response to capsaicin. Considerably higher tissue levels of CGRP-LI were found in the atria (about 30 pmol g-1) than in the ventricles (about 10 pmol g-1). In experiments on the right atria using transmembrane action-potential recordings of myocytes, CGRP induced a prolongation of the action potential concomitantly with an increase in rate and contractile force, which was similar to the effect of noradrenaline. Furthermore, CGRP increased the contractile force and relaxation velocity of the electrically stimulated atria. Capsaicin (10(-7) M) also increased the duration of the atrial action potential. In conclusion, CGRP-like material is released by capsaicin from the isolated guinea-pig heart. Both CGRP and capsaicin prolong the plateau phase of the action potential of atrial myocytes. Therefore, the present data give further evidence that CGRP release from sensory nerves within the heart underlies the cardiostimulatory actions of capsaicin.

Is localization of acute myocardial infarction time related?

A total of 1744 patients admitted to the ICCU with acute myocardial infarction (AMI) were studied in 1462 consecutive days (1982-1986). The aim of the study was to check whether the localization of the AMI was time related. Anterior (anterolateral) (AW) (n = 834) versus inferior-posterior (inferolateral) (IPW) (n = 823) AMI were compared: a third group with isolated lateral wall (LW) AMI (n = 87) was included in the study. Significant differences between monthly AMI localizations were registered, but no rhythmicity (monthly, seasonal) was found. A small absolute prevalence of AW localizations was found in all four seasons, but monthly differences made those differences not statistically significant. Some significant correlation (p less than 0.01) was found between AW AMI domination and daily geomagnetic activity (GMA level I-IV). Only on days with low (quiet) levels of GMA were there more IPW AMIs. Adverse relationship was seen with LW AMI, relatively benign in AMI, was adversely correlated with GMA level (p less than 0.01). Differences in AW/IPW and left/right coronary artery autonomic receptors distribution and flow regulation and/or changes in cardiovascular homeostasis/coagulation, aggregation, viscosity, microcirculation, and so on connected with AMI expansion may be involved in these differences of AMI localization.

Calcitonin gene-related peptide but not substance P mimics capsaicin-induced coronary vasodilation in the pig

The vasodilator effects of the human calcitonin gene-related peptides alpha (hCGRP alpha) and beta (hCGRP beta) were studied in vitro and in vivo in relation to the effects of substance P (SP) and capsaicin on coronary vascular tone in the pig. Both hCGRP alpha and -beta induced a concentration-dependent, long-lasting relaxation of precontracted small (diameter 0.5 mm) pig coronary arteries in vitro. SP was slightly more potent but caused a transient relaxation with a smaller maximal response than CGRP. The relaxation induced by hCGRP alpha and -beta as well as SP was resistant to propranolol and atropine. Capsaicin also induced a long-lasting relaxation of potassium and PGF2 alpha-precontracted coronary arteries. After tachyphylaxis to SP had developed the relaxant effects of CGRP and capsaicin were unchanged. Rubbing the vessels to remove the endothelium completely abolished the relaxant effects of SP while the vasodilation induced by hCGRP alpha as well as capsaicin remained unchanged. Injections of hCGRP alpha, SP or capsaicin into the constantly perfused left anterior descending coronary artery of the pig in vivo caused a dose-dependent decrease in perfusion pressure, suggesting coronary vasodilation. In conclusion, the vasodilator effects of SP in vitro differ from the response to CGRP both with regard to their transient nature, the development of tachyphylaxis and endothelium dependence. The capsaicin-induced coronary vasodilation is therefore more likely to depend on release of CGRP rather than tachykinins from sensory nerves since neither endothelium removal nor SP-tachyphylaxis influenced the capsaicin and CGRP responses.(ABSTRACT TRUNCATED AT 250 WORDS)

Degenerative lesions of a coronary chemoreceptor and nearby neural elements in the hearts of victims of sudden death

A coronary chemoreceptor and its neighboring nerves and ganglia were studied by serial section from the hearts of 11 victims of sudden unexpected death. Either focal or extensive inflammatory destruction was present in the chemoreceptors of 10 of the 11 hearts, and similar abnormalities of local nerves and ganglia were present in all 11 hearts. Because an identical coronary chemoreceptor in the dog has previously been shown to be the site of origin of a powerful reflex with major influence on the electrical activity of the heart, the functional significance of the neural abnormalities found in these 11 human hearts may include important distortion of cardiac rhythm, conduction or repolarization. Future studies are needed to determine the prevalence of such lesions in the hearts of other victims of sudden death and among control subjects, as well as to determine the etiology of this special neuropathology of the heart.