Transient loss of consciousness (TLOC) – it can also be called blackout. TLOC arguably the most complex symptom in all medicine. And most complex to investigate.
The causes of TLOC can vary from vary relatively benign reasons to life-threatening conditions.
For example, TLOC could be due to syncope. Syncope (or faint) is defined as a transient, self-limited loss of consciousness  with an inability to maintain a postural tone that is followed by spontaneous recovery. This definition excludes any other causes of TLOC, and basically, it means that patient in most of the cases will not have structural changes in the heart or any other significant pathology. Syncope happens when there is a sudden drop in blood pressure or heart rate (sometimes both), and there is a temporary drop in the amount of blood that supplies the brain.
The other cardiac possible causes of blackout can include:
Arrhythmias – heartbeat irregularities that can be associated with transient undersupply of the blood to the brain. These are usually due to the blood pressure being to low. Usually, they may be related to structural heart disease or, in rare cases, inherited.
Cardiac conduction problems. We have electrical wiring system in the heart, consisting of the central power station (Sinus Node, located in the right atrium, right chamber of the heart) that transmit the signal to two ventricles via intermediate station called AtrioVentricle Node (AVN). AVN gives rise to two bundles that are called Right Bundle and Left Bundle that supply electricity to the right and left ventricles (lower chambers of the heart) respectively. Either due to gradual ‘tear and wear’ process or due to structural heart disease, there may be a significant block between SN and AVN, causing long pauses. During these pauses, there could be temporal undersupply of blood flow to the brain resulting in a blackout.
Heart Valve Disease, usually significant Aortic Stenosis
Orthostatic hypotension (OH) – a syndrome when there is a decrease of blood pressure by more than 20 mmHg in standing position. OH can cause a blackout, especially if the patient stands up quickly.
Postural Orthostatic Tachycardia Syndrome (POTS) – not very dangerous for the patient in the long term but poses a lot of discomforts and may significantly compromise the quality of life of the patient. Symptoms can include headaches, fatigue and nausea. Also, palpitations, an increase of heart rate from lying to the upright position of greater than 120 beats per minute and at least by 30 from baseline within 10 minutes of standing.
Non-cardiac causes of blackout could be due to the following reasons:
In elderly patients, TLOC could be associated with falls. Therefore, a Care of Elderly Physician’s assessment might be essential here.
Dizziness due to inner ear problems and ENT specialist consultation might be crucial to address this issue.
Psychogenic blackouts. According to heartrhythmalliance.org a psychogenic blackout can be challenging to diagnose. Most often, it occurs in young adults as a result of stress or anxiety. However, the link between blackouts and stress may not be obvious. InPsychogenic’ does not mean that people are ‘putting it on’. A psychogenic blackout is an involuntary reaction of the brain to pressure or distress. Psychogenic blackouts sometimes develop after people have experienced ill-treatment or trauma.
If a patient is seen by a Cardiologist because of the blackout, to rule out Cardiac causes a detailed history will be taken. This will to assess episodes of blackout, the onset, preceding symptoms, duration of blackout and symptoms after regaining consciousness. Family history will be evaluated, as well. The patient will also need:
Echocardiogram to rule out structural heart problems
Heart rate monitoring: either for 24hr or longer depending on symptoms and history
Tilt test will be considered if the diagnosis of syncope is considered. Tilt Test is essential to make a diagnosis when POTS is suspected.
Implantable loop recorder might be considered in cases where a diagnosis is not clear or an episode of TLOC can not be caught by conventional means. An implantable loop recorder is a tiny device implanted under the skin and can stay in the body for up to 3 years. It can record heart trace (ECG) at the time of TLOC.
The above is not an extensive description of blackouts; this is to give a taste of the complexity of the issue and to give an example of a thought process that a Cardiologist is going through when they see a patient with blackouts.
1. Syncope: diagnosis and management.Curr Probl Cardiol. 2015; 40(2):51-86 (ISSN: 1535-6280)Walsh K; Hoffmayer K; Hamdan MH.