Page created on August 14, 2021. Not updated since.
Syncope is a transient loss of consciousness and muscle tone which occurs suddenly, and which resolves spontaneously. It occurs when there is a transient global cerebral hypoperfusion. Syncope is one of multiple causes of transient loss of consciousness (TLOC):
- Cardiac syncope
- Reflex syncope
- Vasovagal syncope
- Carotid sinus syndrome
- Orthostatic syncope
- Epileptic seizures
- Head trauma
- Psychogenic conditions that cause TLOC
When a patient presents with TLOC it’s important to determine the cause. You can read more about distinguishing syncope from epileptic seizures here.
Cardiac syncope is a major risk factor for sudden cardiac death and so it should be ruled out in cases where another definite cause can’t be determined.
Cardiac syncope occurs when the heart is suddenly unable to provide enough perfusion for the brain. This can either be due to an arrhythmia or due to a structural obstruction of the outflow tract of the heart. This type of syncope accounts for only 10% of syncopes. This can be due to:
- Sick sinus syndrome
- Supraventricular tachycardia
- Atrial fibrillation with a fast ventricular rhythm
- WPW syndrome
- Ventricular tachycardia
- AV block
- Structural outflow obstruction
- Left ventricle hypertrophy
- Hypertrophic cardiomyopathy
- Aortic stenosis
- Pulmonary embolism
Vasovagal syncope is the most common cause of syncope and occurs because of a stress trigger which stimulates the vagus nerve, causing an unproportionally large increase in parasympathetic activity, which decreases heart rate and blood pressure. This can occur due to strong pain, fear, a sight of blood, etc. More than 1/3 of people have experiences vasovagal syncope once.
Orthostatic hypotension occurs after standing up if the body can’t initiate the circulatory changes which maintains the blood pressure in the upright position. It occurs most commonly in patients taking antihypertensives.
A thorough history is essential. In patients taking antihypertensives and having low BP, orthostatic syncope is most likely. If syncope occurred after pain, a scare, etc., vasovagal syncope is most likely. The following features are suspicious for cardiac syncope:
- Occurring during exercise
- Occurring in supine position
- Patient has heart disease or is at high risk for it
- Family history of cardiac syncope or sudden cardiac death
If cardiac syncope can’t be reliably ruled out, they should be admitted to be evaluated. All patients should undergo ECG. Echocardiography can diagnose aortic stenosis and hypertrophy. D-dimer and possibly CTPA is PE is possible. If no abnormalities are detected, a Holter ECG may detect a paroxysmal arrhythmia.
An orthostatism test can be used if orthostatic syncope can’t be ruled out. The BP of the patient is measured while supine and after standing up at 0, 1, 3, and 5 minutes. A drop of SBP > 20 mmHg or development of symptoms is a positive test.
Treatment depends on the underlying cause. Orthostatic syncope can be managed with instruction on not to stand up quickly and reduction in antihypertensive dose. Patients should also be instructed to adequately drink and eat salt.
- Afib can be controlled with medication
- WPW can be ablated
- SSS and bradyarrhythmias can be controlled with a pacemaker
- Vfib can be prevented with ICD
- HCMP can be treated with drugs and ICD
Sudden cardiac death
Definition and etiology
Sudden cardiac death (SCD) is defined as unexpected death either:
- Within 1 hour of symptom onset or:
- Within 24 hours of having been observed alive and symptom free
It is suspected that all cases of SCD occur due to ventricular arrhythmias, but the underlying cause of the arrhythmia can vary. SCD is due to an underlying coronary artery disease (CAD) in 80% of cases. It occurs most commonly due to:
- Acute myocardial infarction (leading to acute heart failure or ventricular arrhythmia)
- Chronic ischaemic heart disease (scars leading to ventricular arrhythmia)
- Dilated cardiomyopathy
- Hypertrophic cardiomyopathy
- Arrhythmogenic right ventricular cardiomyopathy (ARVC)
In people with structurally normal hearts, rare conditions like Brugada syndrome and long QT syndrome are common causes of SCD.
Primary prevention of SCD in people without heart disease is the same as primary prevention of CAD.
Primary prevention of SCD in people with heart disease (CAD, heart failure, cardiomyopathy) is important. The following are all class I recommendations:
- Optimal medical therapy (ACEi/ARB, beta-blockers, MRAs) reduces risk for SCD in all patients with left ventricular dysfunction (< 40%), and dilated cardiomyopathy
- ICD implantation reduces risk for SCD in all patients who are at high risk for it, especially:
- Structural heart disease patients who are on optimal medical therapy and are expected to live > 1 year with good functional status
- People with hypertrophic cardiomyopathy or ARVC should avoid participating in competitive sports
- If the patient has a heart condition with high risk for SCD where ablation can be performed (like WPW, certain VTs), ablation reduces risk for SCD
Secondary prevention of SCD refers to prevention in those who’ve already experiences ventricular arrhythmias and is very important. The following are all class I recommendations:
- ICD implantation reduces risk for SCD in people who have survived cardiac arrest
- (In cases where the cardiac arrest was not due to a clearly reversible cause)
- ICD implantation reduces risk for SCD in people who have experienced syncope due to ventricular arrhythmia
However, ICDs are expensive and therefore not implanted in all cases where it is recommended, only the extra high-risk ones.
SCD is preceded by sudden cardiac arrest, but unless the arrest is witnessed and successfully treated, death occurs. The management of sudden cardiac arrest is cardiopulmonary resuscitation, which is described in anaesthesiology and intensive care.