Nervous about the nervous system?

Syncope

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Gwendoline is a 76 year old lady with a long history of uncontrolled type 2 diabetes mellitus who has had several episodes of collapse on standing with her husband describing jerking movements soon after collapsing. He is worried she has developed epilepsy. You see her in general practice and try to determine a cause for her collapse.

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Syncope is a transient loss of consciousness accompanied by loss of postural tone with a rapid onset and spontaneous, complete recovery.

 

The underlying mechanism is transient global cerebral hypo perfusion. We will discuss the mechanism behind neurally mediated and orthostatic hypotension, and briefly outline the causes of cardiac syncope.

 

 

The main causes of syncope are

1. Neurally mediated reflex syncope

2. Postural hypotension (orthostatic hypotension)

3. Cardiac syncope (arrhythmias and structural cardiac disease

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Neurally mediated reflex syncope

Neurally mediated syncope is caused by parasympathetic hypersensitivity and inhibition of sympathetic activity causing peripheral vasodilatation and a decrease in heart rate. This leads to reduced cardiac output and blood pressure, and therefore cerebral hypo perfusion and syncope

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Caused by

• Vasovagal (strong emotions, prolonged standing)

• Situational (weight lifting, coughing, straining, post-prandial, post-micturition)

• Carotid sinus hypersensitivity (turning head quickly, carotid sinus massage)

 

The mechanism behind the parasympathetic over activation from certain triggers (such as pain, food, and urination) is poorly understood.

 

Sustained coughing or straining (weight lifting, during bowel movement) may increase intrathoracic pressure. An increase in intrathoracic pressure causes a decrease in venous return (since blood flows from high à low pressure) causing a reduction in cardiac output and thus cerebral hypoperfusion.

 

Patients with atherosclerosis may have carotid sinus hypersensitivity. The carotid sinus is the site for baroreceptors and narrowing of the carotid artery may mimic increased pressure within the carotid artery thus turning head too quickly or massaging the carotid artery can stimulate the carotid sinus baroreceptor causing decreased sympathetic and increased parasympathetic activity.

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Postural hypotension

Hypotension caused by failure of the autonomic nervous system to accommodate for venous pooling in legs on standing. This results in a fall in blood pressure and therefore cerebral hypo perfusion.

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Normal physiology

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Failure of this system can cause postural hypotension (dizziness and syncope when standing)

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Postural hypotension can occur in

• Healthy individuals, especially adolescents

• Primary autonomic failure: Parkinson’s, multi-system atrophy

• Secondary autonomic failure: diabetic neuropathy, alcoholic neuropathy

• Drugs and polypharmacy e.g. multiple anti-hypertensives

• Age: elderly patients may have decreased baroreceptor responsiveness

• Hypovolaemia: blood loss, dehydration, Addison’s disease

 

 

Postural hypotension is usually diagnosed at the bedside by doing a lying and standing blood pressure and asking if the patient develops any symptoms (since many people may drop their blood pressure on standing but do not become symptomatic due to cerebral auto-regulation).

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Cardiac syncope

Arrhythmias

• Bradycardia

  • AV node block

  • Sick-sinus syndrome (bradycardia-tachycardia syndrome)

 

• Tachycardia

  • Ventricular tachycardia

  • Supraventricular tachycardia

 

Diagnosis will require a 24-hour ECG

 

Structural cardio-pulmonary disease

• Aortic stenosis – especially in a elderly patient. May have ejection systolic murmur.

• Pulmonary embolism – shortness of breath, pleuritic chest pain, DVT

• Hypertrophic obstructive cardiomyopathy – especially in a young patient

 

Patients typically present with syncope on exertion.

 

Investigations include a simple 12 lead ECG, 24-hour ECG tape, echocardiogram and exercise tests.

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Gwendoline is a 76 year old lady with a long history of uncontrolled type 2 diabetes mellitus who has had several episodes of collapse on standing with her husband describing jerking movements soon after collapsing. He is worried she has developed epilepsy. You see her in general practice and try to determine a cause for her collapse.

 

Gwendoline is likely suffering from postural hypotension due to secondary autonomic dysfunction caused by her history of uncontrolled diabetes. Jerking movement for a short duration following a collapse is normal.

 

However it is very important to take a very detailed history from Gwendoline and her partner and examine her thoroughly to rule out other causes (click here for more information).

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It is important to be able to identify a syncopal episode from a seizure:

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