A study by McKhann et al. compared the neurocognitive outcome of people with coronary artery disease (CAD) to heart-healthy controls (people with no cardiac risk factors). People with CAD were subdivided into treatment with CABG, OPCAB and non-surgical medical management. The three groups with CAD all performed significantly lower at baseline than the heart-healthy controls. All groups improved by 3 months, and there were minimal intrasubject changes from 3 to 12 months. No consistent difference between the CABG and off-pump patients was observed. The authors concluded patients with long-standing coronary artery disease have some degree of cognitive dysfunction secondary to cerebrovascular disease before surgery; there is no evidence the cognitive test performance of bypass surgery patients differed from similar control groups with coronary artery disease over a 12-month follow-up period. A related study by Selnes et al. concluded patients with coronary artery bypass grafting did not differ from a comparable nonsurgical control group with coronary artery disease 1 or 3 years after baseline examination. This finding suggests that late cognitive decline after coronary artery bypass grafting previously reported by Newman et al. may not be specific to the use of cardiopulmonary bypass, but may also occur in patients with very similar risk factors for cardiovascular and cerebrovascular disease.

A study by Newman et al. at Duke University Medical Center published in the "New England Journal of Medicine" (NEJM) showed an increased incidence of cognitive decline after coronary artery bypass surgery (CABG), both immediately (53 percent at discharge from hospital) and over time (36 percent six weeks, 24 percent at six months, and 42 percent at five years). This study shows an association of neurocognitive decline with CABG, but does not show causation; the study lacks a control group and is considered level II-3 evidence. Also, the statistical calculation of cognitive decline has been demonstrated as the least reliable due to practice effects, measurement error and the regression to the mean phenomenon.

Subsequent studies have compared "on-pump" CABG to off-pump coronary artery bypass (OPCAB)—essentially establishing controls to compare the incidence of neurocognitive decline in CABG with and without the use of CPB. A small study (60 patients total, 30 in each treatment arm) by Zamvar et al. demonstrated neurocognitive impairment at both 1 week and 10 weeks postoperatively. A larger study (281 patients total) by Van Dijk et al. showed CABG surgery without cardiopulmonary bypass improved cognitive outcomes 3 months after the procedure, but the effects were limited and became negligible at 12 months. Furthermore, the Van Dijk study showed no difference between the on-pump and off-pump groups in quality of life, stroke rate, or all-cause mortality at 3 and 12 months. A study by Jenson et al. published in Circulation found no significant difference in the incidence of cognitive dysfunction 3 months after either OPCAB or conventional on-pump CABG.

Given the above evidence, there is high incidence of neurocognitive deficit post bypass surgery, but the deficits are transient with no permanent neurological impairment. Controlled "on-pump" versus "off-pump" cardiac surgery has only been studied in the setting of CABG and is not necessarily generalizable to other types of cardiac surgery. Recent advancements in transcatheter and percutaneous valve replacement may soon allow comparison of other types of cardiac surgery with and without CPB.

There is some evidence to support the use of methylene blue in the treatment of this condition. Dose 0.5mg/kg on cardiopulmonary bypass.

VPS occurs more frequently after on pump CABG surgery versus off pump CABG surgery. Hypothermia during surgery may also increase ones risk of developing VPS post operatively.

Diagnosis involves consideration of physical features and genetic testing. Presence of split uvula is a differentiating characteristic from Marfan Syndrome, as well as the severity of the heart defects. Loeys-Dietz Syndrome patients have more severe heart involvement and it is advised that they be treated for enlarged aorta earlier due to the increased risk of early rupture in Loeys-Dietz patients. Because different people express different combinations of symptoms and the syndrome was identified in 2005, many doctors may not be aware of its existence, although clinical guidelines were released in 2014-2015. Dr. Harold Dietz, Dr. Bart Loeys, and Dr. Kenneth Zahka are considered experts in this condition.

In terms of the diagnosis of Romano–Ward syndrome the following is done to ascertain the condition(the "Schwartz Score" helps in so doing):

- Exercise test

- ECG

- Family history

Diagnosis of Harlequin syndrome is made when the individual has consistent signs and symptoms of the condition, therefore, it is made by clinical observation. In addition, a neurologist or primary care physician may require an MRI test to rule out similar disorders such as Horner's syndrome, Adie's syndrome, and Ross' syndrome. In an MRI, a radiologist may observe areas near brain or spinal cord for lesions, or any damage to the nerve endings. It is also important that the clinician rules out traumatic causes by performing autonomic function tests. Such tests includes the following: tilt table test, orthostatic blood pressure measurement, head-up test, valsalva maneuver, thermoregulatory sweat test, tendon reflex test, and electrocardiography (ECG). CT scan of the heart and lungs may also be performed to rule out a structural underlying lesion. The medical history of the individual should be carefully noted.

Diagnosis depends on the clinical scenario. However, karyotyping is an essential test for diagnosis.

As there is no known cure, Loeys–Dietz syndrome is a lifelong condition. Due to the high risk of death from aortic aneurysm rupture, patients should be followed closely to monitor aneurysm formation, which can then be corrected with interventional radiology or vascular surgery.

Previous research in laboratory mice has suggested that the angiotensin II receptor antagonist losartan, which appears to block TGF-beta activity, can slow or halt the formation of aortic aneurysms in Marfan syndrome. A large clinical trial sponsored by the National Institutes of Health is currently underway to explore the use of losartan to prevent aneurysms in Marfan syndrome patients. Both Marfan syndrome and Loeys–Dietz syndrome are associated with increased TGF-beta signaling in the vessel wall. Therefore, losartan also holds promise for the treatment of Loeys–Dietz syndrome. In those patients in which losartan is not halting the growth of the aorta, irbesartan has been shown to work and is currently also being studied and prescribed for some patients with this condition.

If an increased heart rate is present, atenolol is sometimes prescribed to reduce the heart rate to prevent any extra pressure on the tissue of the aorta. Likewise, strenuous physical activity is discouraged in patients, especially weight lifting and contact sports.

Treatment for Romano–Ward syndrome can "deal with" the imbalance between the right and left sides of the sympathetic nervous system which may play a role in the cause of this syndrome. The imbalance can be temporarily abolished with a left stellate ganglion block, which shorten the QT interval. If this is successful, surgical ganglionectomy can be performed as a permanent treatment.Ventricular dysrhythmia may be managed by beta-adrenergic blockade (propranolol)

In August 2016, researchers at the Instituto de Assistência dos Servidores do Estado do Rio de Janeiro used botulinum toxin as a method to block the acetylcholine release from the presynaptic neurons. Although they have seen a reduction in one sided flushing, sweating still occurs.

There have been case studies of individuals whom have experienced this syndrome after an operation. Two patients, a 37-year-old and 58-year-old female patients suffering from metastatic cancer were scheduled for placement of an intrathecal pump drug delivery system. After the intrathecal pump was placed, certain medications were given to the patients. Once the medications were administered, both patients had one sided facial flushes, closely resembling Harlequin Syndrome. Patients were given neurological exams to confirm that their nerves were still intact. An MRI was performed and showed no significant evidence of bleeding or nerve compression. After close observation for 16 hours, symptoms of the Harlequin syndrome was diminished and both patients did not have another episode.

Another case study was based on a 6-year-old male visiting an outpatient setting for one sided flushes during or after physical activity or exposed to heat. Vitals, laboratory tests, and CT scans were normal. Along with the flushes, the right pupil was 1.5 mm in size, while the left pupil was 2.5 mm in size; however, no ptosis, miosis, or enophthalmos was noted. The patient also had an MRI scan to rule out any lesion near the brain or spinal cord. No abnormalities were noted and the patient did not receive any treatments. The patient was diagnosed with idiopathic Harlequin syndrome.

Although the mechanism is still unclear, the pathophysiology of this condition, close monitoring, and reassurance are vital factors for successful management.

Diagnosis can be made by EEG. In case of epileptic spasms, EEG shows typical patterns.

Various strategies have been proposed to prevent the development of metabolic syndrome. These include increased physical activity (such as walking 30 minutes every day), and a healthy, reduced calorie diet. Many studies support the value of a healthy lifestyle as above. However, one study stated these potentially beneficial measures are effective in only a minority of people, primarily due to a lack of compliance with lifestyle and diet changes. The International Obesity Taskforce states that interventions on a sociopolitical level are required to reduce development of the metabolic syndrome in populations.

The Caerphilly Heart Disease Study followed 2,375 male subjects over 20 years and suggested the daily intake of a pint (~568 ml) of milk or equivalent dairy products more than halved the risk of metabolic syndrome. Some subsequent studies support the authors' findings, while others dispute them. A systematic review of four randomized controlled trials found that a paleolithic nutritional pattern improved three of five measurable components of the metabolic syndrome in participants with at least one of the components.

The World Health Organization 1999 criteria require the presence of any one of diabetes mellitus, impaired glucose tolerance, impaired fasting glucose or insulin resistance, AND two of the following:

- Blood pressure: ≥ 140/90 mmHg

- Dyslipidemia: triglycerides (TG): ≥ 1.695 mmol/L and high-density lipoprotein cholesterol (HDL-C) ≤ 0.9 mmol/L (male), ≤ 1.0 mmol/L (female)

- Central obesity: waist:hip ratio > 0.90 (male); > 0.85 (female), or body mass index > 30 kg/m

- Microalbuminuria: urinary albumin excretion ratio ≥ 20 µg/min or albumin:creatinine ratio ≥ 30 mg/g

Occasionally the syndrome is referred to as "idiopathic" West syndrome, when a cause cannot be determined. Important diagnostic criteria are:

- Regular development until the onset of the attacks or before the beginning of the therapy

- no pathological findings in neurological or neuroradiological studies

- no evidence of a trigger for the spasms

Those are becoming rare due to modern medicine.

Individuals with LGL syndrome do not carry an increased risk of sudden death. The only morbidity associated with the syndrome is the occurrence of paroxysmal episodes of tachycardia which may be of several types, including sinus tachycardia, supraventricular tachycardia, atrial fibrillation, atrial flutter, or even ventricular tachycardia.

Syndactyly and other deformities are typically observed and diagnosed at birth. Long QT syndrome sometimes presents itself as a complication due to surgery to correct syndactyly. Other times, children collapse spontaneously while playing. In all cases it is confirmed with ECG measurements. Sequencing of the CACNA1C gene further confirms the diagnosis.

Ambulatory monitoring of the electrocardiogram (ECG) may be necessary because arrhythmias are transient. The ECG may show any of the following:

- Inappropriate sinus bradycardia

- Sinus arrest

- Sinoatrial block

- Tachy-Brady Syndrome

- Atrial fibrillation with slow ventricular response

- A prolonged asystolic period after a period of tachycardias

- Atrial flutter

- Ectopic atrial tachycardia

- Sinus node reentrant tachycardia

- Wolff-Parkinson-White syndrome

Electrophysiologic tests are no longer used for diagnostic purposes because of their low specificity and sensitivity. Cardioinhibitory and vasodepressor forms of sick sinus syndrome may be revealed by tilt table testing.

Anticholinergic drugs have been reported to be extremely effective in 40% of the patients with the Pisa syndrome. Patients with Pisa syndrome that is resistant to anticholinergic drugs is mostly resolved by the reduction of the administration of the antipsychotic drugs as previously mentioned. While the specific pathology underlying idiopathic Pisa syndrome is unknown, the administration of anticholinergic drugs has provided resolution in known cases.

There are two lines of treatment for Pisa syndrome. The first line entails discontinuation or reduction in dose of the antipsychotic drug(s). The second line of treatment is an anticholinergic medication. A pharmacological therapy for Pisa syndrome caused by prolonged use of antipsychotic drugs has not been established yet.

It is named for Mary Holt and Samuel Oram, who published a paper on it in 1960.

LGL syndrome is diagnosed on the basis of the surface EKG in a symptomatic individual with a PR interval less than or equal to 0.12 second (120 ms) with normal QRS complex configuration and duration. It can be distinguished from WPW syndrome because the delta waves seen in WPW syndrome are not seen in LGL syndrome. It is a clinical diagnosis that came about before the advent of electrophysiology studies. Be aware, however, that not all WPW EKG's have a delta wave; the absence of a delta wave does not conclusively rule out WPW.

Carrier testing for Roberts syndrome requires prior identification of the disease-causing mutation in the family. Carriers for the disorder are heterozygotes due to the autosomal recessive nature of the disease. Carriers are also not at risk for contracting Roberts syndrome themselves. A prenatal diagnosis of Roberts syndrome requires an ultrasound examination paired with cytogenetic testing or prior identification of the disease-causing ESCO2 mutations in the family.

Diagnosis of oculocerebrorenal syndrome can be done via genetic testing Among the different investigations that can de done are:

- Urinalysis

- MRI

- Blood test

The prognosis for patients diagnosed with Timothy syndrome is very poor. Of 17 children analyzed in one study, 10 died at an average age of 2.5 years. Of those that did survive, 3 were diagnosed with autism, one with an autism spectrum disorder, and the last had severe delays in language development. One patient with atypical Timothy syndrome was largely normal with the exception of heart arrhythmia. Likewise, the mother of two Timothy syndrome patients also carried the mutation but lacked any obvious phenotype. In both of these cases, however, the lack of severity of the disorder was due to mosaicism.