Progress, challenges and perspectives in the management of hypopituitarism.

Hypopituitarism is a rare endocrine disorder characterized by insufficient hormone secretion from the pituitary gland. This condition leads to deficient production of one or more pituitary hormones, including growth hormone (GH), thyroid-stimulating hormone (TSH), luteinizing hormone (LH), follicle-stimulating hormone (FSH), adrenocorticotropic hormone (ACTH), and antidiuretic hormone (ADH), also called arginine vasopressin (AVP). Symptoms vary widely and are often not, late recognized.Diagnosis typically involves a thorough clinical evaluation, hormone level assessments, and neuroimaging studies to identify underlying causes. Treatment aims to replace deficient hormones and address the underlying cause and related complications when possible. In this special issue we address diagnosis, comorbidities, and management of hypopituitarism. We hope that it will help healthcare professionals to manage their patients.

Diagnosing and treating anterior pituitary hormone deficiency in pediatric patients.

Hypopituitarism, or the failure to secrete hormones produced by the anterior pituitary (adenohypophysis) and/or to release hormones from the posterior pituitary (neurohypophysis), can be congenital or acquired. When more than one pituitary hormone axis is impaired, the condition is known as combined pituitary hormone deficiency (CPHD). The deficiency may be primarily due to a hypothalamic or to a pituitary disorder, or concomitantly both, and has a negative impact on target organ function. This review focuses on the pathophysiology, diagnosis and management of anterior pituitary hormone deficiency in the pediatric age. Congenital hypopituitarism is generally due to genetic disorders and requires early medical attention. Exposure to toxicants or intrauterine infections should also be considered as potential etiologies. The molecular mechanisms underlying the fetal development of the hypothalamus and the pituitary are well characterized, and variants in the genes involved therein may explain the pathophysiology of congenital hypopituitarism: mutations in the genes expressed in the earliest stages are usually associated with syndromic forms whereas variants in genes involved in later stages of pituitary development result in non-syndromic forms with more specific hormone deficiencies. Tumors or lesions of the (peri)sellar region, cranial radiation therapy, traumatic brain injury and, more rarely, other inflammatory or infectious lesions represent the etiologies of acquired hypopituitarism. Hormone replacement is the general strategy, with critical periods of postnatal life requiring specific attention.

Diagnosis and therapeutic approach to bone health in patients with hypopituitarism.

The results of many studies in recent years indicate a significant impact of pituitary function on bone health. The proper function of the pituitary gland has a significant impact on the growth of the skeleton and the appearance of sexual dimorphism. It is also responsible for achieving peak bone mass, which protects against the development of osteoporosis and fractures later in life. It is also liable for the proper remodeling of the skeleton, which is a physiological mechanism managing the proper mechanical resistance of bones and the possibility of its regeneration after injuries. Pituitary diseases causing hypofunction and deficiency of tropic hormones, and thus deficiency of key hormones of effector organs, have a negative impact on the skeleton, resulting in reduced bone mass and susceptibility to pathological fractures. The early appearance of pituitary dysfunction, i.e. in the pre-pubertal period, is responsible for failure to achieve peak bone mass, and thus the risk of developing osteoporosis in later years. This argues for the need for a thorough assessment of patients with hypopituitarism, not only in terms of metabolic disorders, but also in terms of bone disorders. Early and properly performed treatment may prevent patients from developing the bone complications that are so common in this pathology. The aim of this review is to discuss the physiological, pathophysiological, and clinical insights of bone involvement in pituitary disease.

[Multidisciplinary efforts to improve the diagnosis and treatment of cirrhosis due to anterior pituitary hypopituitarism].

More and more clinical evidence confirms that hypopituitary dysfunction can lead to liver cirrhosis. The causes of hypopituitary dysfunction include sellarneoplastic diseases, hereditary diseases, perinatal adverse events, etc. Clinically, growth hormone deficiency (GHD) often the first cause in hypopituitary dysfunction.Hypopituitary dysfunction, especially GHD, can lead to liver cirrhosis, which in turn can result in damage to multiple organs such as the secondary lungs, spleen, and heart.Therefore, its clinical manifestations are complex, and the patients are first diagnosed in various departments.Reliable clinical observations have shown that GH replacement therapy at the early stage of the disease can effectively prevent and reverse the progression of cirrhosis, or even avoid inappropriate or unnecessary combined transplantation of liver or liver-related organs.Multidisciplinary collaboration and attention to the new findings that hypopituitary dysfunction can lead to liver cirrhosis will help to improve the accurate diagnosis and treatment of liver cirrhosis.

Endocrine Dysfunction After Traumatic Brain Injury: An Ignored Clinical Syndrome?

Traumatic brain injury (TBI) incurs substantial health and economic burden, as it is the leading reason for death and disability globally. Endocrine abnormalities are no longer considered a rare complication of TBI. The reported prevalence is variable across studies, depending on the time frame of injury, time and type of testing, and variability in hormonal values considered normal across different studies. The present review reports evidence on the endocrine dysfunction that can occur after TBI. Several aspects, including the pathophysiological mechanisms, clinical consequences/challenges (in the acute and chronic phases), screening and diagnostic workup, principles of therapeutic management, and insights on future directions/research agenda, are presented. The management of hypopituitarism following TBI involves hormonal replacement therapy. It is essential for health care providers to be aware of this complication because at times, symptoms may be subtle and may be mistaken to be caused by brain injury itself. There is a need for stronger evidence for establishing recommendations for optimum management so that they can be incorporated as standard of care in TBI management.

Diagnosis and Management of Pituitary Adenomas: A Review.

Importance: Pituitary adenomas are neoplasms of the pituitary adenohypophyseal cell lineage and include functioning tumors, characterized by the secretion of pituitary hormones, and nonfunctioning tumors. Clinically evident pituitary adenomas occur in approximately 1 in 1100 persons. Observations: Pituitary adenomas are classified as either macroadenomas (≥10 mm) (48% of tumors) or microadenomas (<10 mm). Macroadenomas may cause mass effect, such as visual field defects, headache, and/or hypopituitarism, which occur in about 18% to 78%, 17% to 75%, and 34% to 89% of patients, respectively. Thirty percent of pituitary adenomas are nonfunctioning adenomas, which do not produce hormones. Functioning tumors are those that produce an excess of normally produced hormones and include prolactinomas, somatotropinomas, corticotropinomas, and thyrotropinomas, which produce prolactin, growth hormone, corticotropin, and thyrotropin, respectively. Approximately 53% of pituitary adenomas are prolactinomas, which can cause hypogonadism, infertility, and/or galactorrhea. Twelve percent are somatotropinomas, which cause acromegaly in adults and gigantism in children, and 4% are corticotropinomas, which secrete corticotropin autonomously, resulting in hypercortisolemia and Cushing disease. All patients with pituitary tumors require endocrine evaluation for hormone hypersecretion. Patients with macroadenomas additionally require evaluation for hypopituitarism, and patients with tumors compressing the optic chiasm should be referred to an ophthalmologist for formal visual field testing. For those requiring treatment, first-line therapy is usually transsphenoidal pituitary surgery, except for prolactinomas, for which medical therapy, either bromocriptine or cabergoline, is usually first line. Conclusions and Relevance: Clinically manifest pituitary adenomas affect approximately 1 in 1100 people and can be complicated by syndromes of hormone excess as well as visual field defects and hypopituitarism from mass effect in larger tumors. First-line therapy for prolactinomas consists of bromocriptine or cabergoline, and transsphenoidal pituitary surgery is first-line therapy for other pituitary adenomas requiring treatment.

Sheehan syndrome.

Sheehan syndrome is an underestimated cause of hypopituitarism, which can be either partial or complete. It results from ischaemic necrosis of anterior pituitary during peripartum period leading to loss of one or more pituitary cell lines. Hyperplasia of pituitary gland during pregnancy increases demand for blood supply and at the same time compresses the pituitary gland. Severe postpartum haemorrhage leads to hypovolaemia and vasospasm of supplying vessels resulting in infarction of pituitary tissue. Congenital or acquired thrombophilia and autoimmunity exaggerate this phenomenon. Presentation is usually delayed by many years. It presents with symptoms of anterior pituitary hormone loss after a delay of many years. Rarely presentation may be acute or involve posterior pituitary as well. Low basal or stimulated pituitary hormones along with classic clinical setting clinches the diagnosis. Replacement of deficient hormones is the mainstay of treatment, however emphasis on better obstetric care to common masses would help to eradicate the disease in future.

Hypothalamic-pituitary fungal infection causing panhypopituitarism.

Madam LPS, a 69 years old lady complained of left eye blurring of vision since January 2017. It was associated with left orbital swelling with chemosis, eye redness, epiphora, several episodes of self-limiting epistaxis and bilateral ophthalmoplegia. Other neurological examinations and cerebellar systems were intact. Magnetic Resonance Imaging (MRI) Brain and Orbit were performed, depicting a sellar mass with suprasellar extension with blood investigations results showed panhypopituitarism. She underwent bilateral orbital decompression. Trans-nasal endoscopic biopsy showed suppurative granulomatous lesion, which cultured Candida Albicans and Candida Galbrata. She was started on antifungal and hormonal replacement therapy for panhypopituitarism. Unfortunately, she did not respond well to treatment as repeated MRI Brain on December 2018 showed increase in size of sellar mass causing obstructive hydrocephalus and increasing size of left orbital lesion. She was counselled for another debulking surgery with a ventriculoperitoneal (VP) shunt. HPE taken were reported as chronic inflammatory process in favour to fungal infection. Pituitary infections may mimic pituitary mass. Some may exhibit symptoms of panhypopituitarism as well. Thus, physical examination, MRI brain imaging as well as HPE of biopsy are important aids to achieve diagnosis. Optimal treatment of fungal pituitary abscess includes transsphenoidal surgery combined with antifungal therapy.

Patient-Centered Outcomes with Pituitary and Parasellar Disease.

Over the last 2 decades, advances in the diagnosis and management of pituitary diseases have made it possible to attain an endocrine "cure" in a large proportion of patients. In other words, tumors can be excised or controlled with drugs, mass effects of the lesion on surrounding structures can be solved, and pituitary deficiencies can be substituted with all relevant hormones. While this is considered a satisfactory outcome for health care providers, patients often suffer from an aftermath of prior endocrine dysfunction exposure, with irreversible effects, both physically and psychologically, which have a great impact on their everyday life. Diagnostic delay, often of several years, adds a negative impact on health perception. This affects their social, professional, and family domains and determines their future life. Understanding that this may occur is important, and health care providers should offer information to prepare the patient for this difficult journey, especially in the case of acromegaly, Cushing disease, or hypopituitarism. In order to maintain a good quality of life (QoL) in the long-term, patients need to adapt to this new situation, something that may be difficult, since they often cannot continue with all the activities and rhythm they used to do. Depression is often the consequence of maladaptation to the new situation, leading to impaired QoL.

Clinical Characteristics, Management, and Treatment Outcomes of Primary Hypophysitis: A Monocentric Cohort.

Primary hypophysitis (PH) is a rare autoimmune inflammatory disease of the pituitary gland. The aim of the study was to evaluate clinical characteristics, disease management, and outcomes of cases with PH. Medical records of PH patients admitted to Hacettepe University Hospital between 1999 and 2017 were analyzed retrospectively. Paraffin-embedded pathology blocks were obtained for both re-examination and IgG4 immunostaining. Twenty PH patients (15 females, 5 males) were evaluated. Mean age at diagnosis was 41.5±13.4 years. Some form of hormonal disorder was present in 63.2% of cases, hypogonadism (66.6%) being the most common. Panhypopituitarism was present in 36.8%. All patients had pituitary gland enlargement on magnetic resonance imaging; stalk thickening and loss of neurohypophyseal bright spot were present in 17.6 and 23.5%, respectively. Lymphocytic hypophysitis was the most common histopathological subtype (50%). Among pathology specimens available for IgG and IgG4 immunostaining (n=10), none fulfilled the criteria for IgG4-related hypophysitis. Four patients were given glucocorticoid treatment in diverse protocols; as initial therapy in 3. Sixteen cases underwent surgery, 7 of whom due to neuro-ophthalmologic involvement. Only 1 patient was observed without any intervention. Reduction of pituitary enlargement was seen in all surgical and glucocorticoid treated cases. None of the surgical patients showed hormonal improvement while one case in glucocorticoid group improved. PH should be considered in the differential diagnosis of sellar masses causing hormonal deficiencies. MRI findings are usually helpful, but not yet sufficient for definitive diagnosis of PH. Treatment usually improves symptoms and reduces sellar masses while hormonal recovery is less common.

Nasopharyngeal B-cell lymphoma with pan-hypopituitarism and oculomotor nerve palsy: a case report and review of the literature.

BACKGROUND: Primary nasopharyngeal lymphoma (NPL) is a very rare tumor of Waldeyer ring (WR) lymphoid tissue. It is challenging to differentiate lymphoma infiltration of pituitary from a pituitary adenoma, meningioma infiltration, and other sellar lesions to plan a suitable treatment strategy. We presented for the first time a unique case of NPL with an unusual presentation of oculomotor nerve palsy associated with pan-pituitary involvement in a diabetic patient. CASE PRESENTATION: A 64-year old diabetic woman with no previous history of malignancy presented with intermittent diplopia for about the last nine months. Severe headache, left eye ptosis and hypoglycemic episodes were added to her symptoms after a while. Further complaints include generalized weakness, loss of appetite, generalized musculoskeletal pain, and 6-7 kg weight loss within six months. Her family history was unremarkable. Physical examinations of eyes indicated left eye 3rd, 4th, and 6th nerve palsy. But, she was not anisocoric, and the pupillary reflexes were normal on both eyes. No lymphadenopathy, organomegaly and other abnormalities were found. Magnetic resonance imaging (MRI) showed a heterogeneous enhancement in the seller and suprasellar regions, enlargement of the stalk, parasellar dural enhancement and thickening of the sphenoid sinus without bone erosion. Also, both cavernous sinuses were infiltrated and both internal carotid arteries were encased by the neoplastic lesion. It suggested an infiltrative neoplastic lesion which compressed the cranial nerves. Pituitary hormone levels assessment indicated a pan-hypopituitarism. Following nasopharyngeal mucosal biopsy, the immunohistochemistry (IHC) findings revealed a low-grade non-Hodgkin's B-cell lymphoma. Systemic workup, including cerebrospinal fluid (CSF) studies, bone marrow aspiration, chest and abdominopelvic high-resolution computed tomography (HRCT) indicated no other involvement by the lymphoma. After chemotherapy courses, central adrenal insufficiency, partial central diabetes incipidious (CDI) and central hypothyroidism have been resolved. To our best knowledge, we found 17 cases of NPL with cranial nerve palsy, 1 case of NPL with pan-hypopituitarism and no NPL case with both cranial nerve palsy and pituitary dysfunction. CONCLUSIONS: The incidence of cranial neuropathy in patients with diabetes should not merely be attributed to diabetic neuropathy without further evaluation.

Primary and Ipilimumab-induced Hypophysitis: A Single-center Case Series.

PURPOSE: To present a case series of primary and immunotherapy-related secondary hypophysitis. METHODS: A single-center retrospective chart review was performed at the University of British Columbia, Vancouver, Canada. Eleven cases of primary hypophysitis and 2 cases of immunotherapy-related secondary hypophysitis were included. Of the 11 primary cases, 6 were diagnosed clinically without biopsy. RESULTS: In primary hypophysitis, headache was the most common presenting symptom (6/11; 55%) and stalk enlargement the prevailing radiologic sign (8/11; 73%). Central adrenal insufficiency (4/11; 36%), central hypothyroidism (4/11; 36%), and central diabetes insipidus (CDI) (4/11; 36%) were the most common pituitary deficiencies at presentation. Initial management included surgery (4/11; 36%), supraphysiologic steroids (2/11; 18%), or observation (6/11; 55%). Outcomes assessed included radiologic improvement (8/9; 89%), improvement in mass symptoms (4/7; 57%), anterior pituitary recovery (1/7; 14%), and CDI recovery (0/4; 0%). In immunotherapy-related hypophysitis either under observation or supraphysiologic steroid therapy, the inflammatory mass resolved and pituitary dysfunction persisted. CONCLUSIONS: In primary hypophysitis, the inflammatory pituitary mass typically resolves and hypopituitarism persists. In the absence of severe or progressive neurologic deficits, a presumptive clinical diagnosis and conservative medical management should be attempted. In the absence of severe features, immunotherapy-related hypophysitis may be managed effectively without the use of supraphysiologic steroids.

Diagnosis and management of hypopituitarism.

PURPOSE OF REVIEW: This review summarizes pituitary function, and the clinical presentation and treatment of hypopituitarism. RECENT FINDINGS: Updates in the field include new guidelines and meta-analyses on the diagnosis and treatment of select hormone deficiencies, novel treatment options, and advances in next generation sequencing technology. SUMMARY: Hypopituitarism is defined as partial or complete loss of a single or multiple pituitary hormones. The clinical presentation of hypopituitarism varies depending on the number and severity of hormone deficiencies. Treatment involves the physiologic replacement of the individual end-organ hormone deficiencies and requires close lifelong monitoring.

Major Issues of Care in Thalassemia Major Children Refugees.

Beta thalassemia major (ßTM) is the most common inherited hemoglobinopathy. Management essentially focuses on preventing and treating complications. Conventional treatment is based on a regular blood transfusion program, and chelation therapy. Management essentially focuses on preventing and treating complications. Severe complications of ßTM are very rarely seen in children in Europe. In the context of the migrant crisis, pediatricians will be confronted with the challenge of managing severe complicated ßTM. We report the case of 2 Syrian 10-year-old twin girls who arrived to France with numerous and severe complications of ßTM: hemochromatosis, alloimmunization, hypopituitarism, osteopenia… Their clinical management, which led to successful vital and functional improvement, is reported in this article.

A pituitary abscess with one year follow-up after conservative treatment: A case report.

Pituitary abscess (PA) is a rare intrasellar infectious disease presented in less than one percent of all cases of pituitary disease.We reported a case of a 58-year-old woman with a history of type 2 diabetes (T2DM) exhibited with headaches, nasal discharge, anosmia, diabetes insipidus and hypopituitarism due to PA, she was diagnosed based on clinical presentations, endocrine examination and MRI image features. She was treated with nasal wash and antibiotic therapy without surgical intervention. She has received hormone replacement therapy for one year and her condition has gradually become stabilized. Meanwhile, the lesion of MRI image didn't become serious after one year. Conservative treatment might be an option for the patients with PA, those rejected operation or in a stable condition.

The screening and management of pituitary dysfunction following traumatic brain injury in adults: British Neurotrauma Group guidance.

Pituitary dysfunction is a recognised, but potentially underdiagnosed complication of traumatic brain injury (TBI). Post-traumatic hypopituitarism (PTHP) can have major consequences for patients physically, psychologically, emotionally and socially, leading to reduced quality of life, depression and poor rehabilitation outcome. However, studies on the incidence of PTHP have yielded highly variable findings. The risk factors and pathophysiology of this condition are also not yet fully understood. There is currently no national consensus for the screening and detection of PTHP in patients with TBI, with practice likely varying significantly between centres. In view of this, a guidance development group consisting of expert clinicians involved in the care of patients with TBI, including neurosurgeons, neurologists, neurointensivists and endocrinologists, was convened to formulate national guidance with the aim of facilitating consistency and uniformity in the care of patients with TBI, and ensuring timely detection or exclusion of PTHP where appropriate. This article summarises the current literature on PTHP, and sets out guidance for the screening and management of pituitary dysfunction in adult patients with TBI. It is hoped that future research will lead to more definitive recommendations in the form of guidelines.

Pituitary stalk interruption syndrome: cause, clinical manifestations, diagnosis, and management.

PURPOSE OF REVIEW: Pituitary stalk interruption syndrome (PSIS) is characterized by a thin or absent pituitary stalk, hypoplasia of the adenohypophysis, and ectopic neurohypophysis. PSIS manifestations include a wide spectrum of clinical phenotypes and pituitary hormone deficiencies of variable degree and timing of onset. In this review, recent advances with respect to the cause of PSIS, clinical characteristics leading to earlier diagnosis, and management are outlined. RECENT FINDINGS: Diagnosis of PSIS is often delayed probably because clinical findings such as neonatal hypoglycemia, cholestasis, and/or micropenis as well as decreasing growth velocity are not appropriately and timely validated. Recently, molecular defects in various genes have been associated with PSIS albeit in a small number of cases. These findings suggest that PSIS belongs to the spectrum of holoprosencephaly-related defects. Phenotype-genotype discordance and the existence of asymptomatic carriers of a given molecular aberration indicate that penetrance may be modified favorably or unfavorably by the presence of other genetic and/or environmental factors. SUMMARY: PSIS constitutes an antenatal anatomical defect. Neonatal hypoglycemia, cholestasis, and/or micropenis with or without growth deficit should raise the possibility of combined pituitary hormone deficiency, a life-threatening condition in cases of coexisting cortisol deficiency. It is important to search for molecular defects in all PSIS cases, as precise identification of the cause is a prerequisite for genetic counseling.

The development and validation of the Leiden Bother and Needs Questionnaire for patients with pituitary disease: the LBNQ-Pituitary.

BACKGROUND: Patients report persisting impairment in quality of life (QoL) after treatment for pituitary disease. At present, there is no questionnaire to assess (a) whether patients with pituitary disease are bothered by these consequences, and (b) their needs for support. OBJECTIVE: To develop and validate a disease-specific questionnaire for patients with pituitary disease which incorporates patient perceived bother related to the consequences of the disease, and their needs for support. METHODS: Items for the Leiden Bother and Needs Questionnaire for patients with pituitary disease (LBNQ-Pituitary) were formulated based on results of a recent focus group study (n = 49 items). 337 patients completed the LBNQ-Pituitary and six validated QoL questionnaires (EuroQoL-5D, SF-36, MFI-20, HADS, AcroQol, CushingQoL). Construct validity was examined by exploratory factor analysis. Reliabilities of the subscales were calculated with Cronbach's alphas, and concurrent validity was assessed by calculating Spearman's correlations between the LBNQ-Pituitary and the other measures. RESULTS: Factor analyses produced five subscales (i.e., mood problems, negative illness perceptions, issues in sexual functioning, physical and cognitive complaints, issues in social functioning) containing a total of 26 items. All factors were found to be reliable (Cronbach's alphas all ≥.765), and the correlations between the dimensions of the LBNQ-Pituitary and other questionnaires (all P ≤ .0001) demonstrated convergent validity. CONCLUSIONS: The LBNQ-Pituitary can be used to assess the degree to which patients are bothered by the consequences of the pituitary disease, as well as their needs for support. It could also facilitate an efficient assessment of patients' needs for support in clinical practice. We postulate that paying attention to needs for support will lead to optimal patient care (e.g., improvement in psychosocial care), and positively affect QoL.

Hypopituitarism in the elderly: a narrative review on clinical management of hypothalamic-pituitary-gonadal, hypothalamic-pituitary-thyroid and hypothalamic-pituitary-adrenal axes dysfunction.

Hypopituitarism is an uncommon and under-investigated endocrine disorder in old age since signs and symptoms are unspecific and, at least in part, can be attributed to the physiological effects of aging and related co-morbidities. Clinical presentation is often insidious being characterized by non-specific manifestations, such as weight gain, fatigue, low muscle strength, bradipsychism, hypotension or intolerance to cold. In these circumstances, hypopituitarism is a rarely life-threatening condition, but evolution may be more dramatic as a result of pituitary apoplexy, or when a serious condition of adrenal insufficiency suddenly occurs. Clinical presentation depends on the effects that each pituitary deficit can cause, and on their mutual relationship, but also, inevitably, it depends on the severity and duration of the deficit itself, as well as on the general condition of the patient. Indeed, indications and methods of hormone replacement therapy must include the need to normalize the endocrine profile without contributing to the worsening of intercurrent diseases, such as those of glucose and bone metabolism, and the cardiovascular system, or to the increasing cancer risk. Hormonal requirements of elderly patients are reduced compared to young adults, but a prompt diagnosis and appropriate treatment of pituitary deficiencies are strongly recommended, also in this age range.

Adrenal insufficiency causes life-threatening arrhythmia with prolongation of QT interval.

A 63-year-old woman who had hypopituitarism was re-admitted to our hospital because of fever, diarrhea and disturbance of consciousness with life-threatening arrhythmia due to prolongation of the QT interval. She has been treated with hydrocortisone consequently, and has shown few ventricular arrhythmias with normalization of the QT interval. There have been several reports showing the case of prolonged QT interval with adrenal insufficiency, but there are few reports of isolated adrenocorticotropic hormone deficiency without any electrolytes imbalance that showed polymorphic ventricular tachycardia associated with QT prolongation. We discuss some possible mechanisms of how adrenal insufficiency causes life-threatening arrhythmia. Since lack of glucocorticoid hormone might induce prolongation of the QT interval, patients with adrenal insufficiency should be paid attention as candidates of lethal arrhythmias particularly when exposed to excessive stresses.