There are different types of arrhythmia (a condition in which the heart beats with a rhythm that is irregular, too fast, or too slow) that may cause syncope:

  • Bradyarrhythmias – This is a significant arrhythmic cause of syncope, especially in the elderly. One type is sinus bradycardia (a type of sinus node dysfunction in which the sinus node – the heart’s natural pacemaker from the right atrium – is not working efficiently, and the result is bradycardia – a slow heart rate.) Another type is atrioventricular conduction system disease, impairment of the electrical flow between the atria (upper chambers) and ventricles (lower chambers) that can cause significant bradycardia or pauses in heart rhythm by blocking one or more impulses to travel to the ventricles
  • Tachyarrhythmias – These are arrhythmias due to a very fast heartbeat.
  • Paroxysmal supraventricular and ventricular tachycardias (occasional episodes of very rapid heartbeat above or in the ventricles, that start and stop suddenly) – Supraventricular arrhythmias with extreme fast heart rates, even though non-life threatening, can cause hemodynamic (blood flow) compromise with syncope such as atrial fibrillation (a very fast and irregular contraction of the atria).

In patients in whom left ventricle dysfunction is seen, or in those who have inherited syndromes such as long QT syndrome or Brugada syndrome (electrical abnormalities at the cellular level), or other structural abnormalities of the myocardium (heart muscle), one of two conditions may cause syncope: ventricular tachycardia or ventricular fibrillation (V-fib):

  • Ventricular Tachycardia (V-tach) – This is a rapid heartbeat that originates in the ventricles. Because of the rapid and dys-synchronized heartbeats, the heart is unable to adequately fill with blood, so less blood is available to pump throughout the body. V-tach can be serious, especially in those with existing heart disease. The condition is usually seen in people who have had a previous heart attack (myocardial infarction, or MI) which has created a scar that leads to a short circuit as the electrical impulses attempt to circumvent the scar.
  • Ventricular Fibrillation (V-fib) – In this condition, an erratic, disjointed firing of electrical impulses from the ventricles causes the ventricles to quiver, and they cannot produce an effective contraction. This means that they cannot deliver an adequate blood supply to the rest of the body.

Note: Both V-tach and V-fib are medical emergencies that must be treated with defibrillation (delivering an energy shock to the heart muscle) as soon as possible, if they do not terminate spontaneously, to reset the heart electricity and prevent death.

Reversible Causes of Syncope

These can easily be controlled once identified:

  • Implanted device (pacemaker, implantable cardioverter-defibrillator) malfunction
  • Drug-induced arrhythmias

When an arrhythmia is suspected and the episodes of syncope do not occur often enough to be “caught” via 24-hour or even 30 days of continuous external monitoring, the test that is often regarded as the most effective is the Implantable Loop Recorder (ILR). This is used if you are known to have a high cardiovascular risk for syncope, and it is considered the gold standard for diagnosing the cause of syncope when other tests have failed to do so.