These contractions originate from any point in the atria or ventricles (the heart consists of two atria and two ventricles), but occur just a very small fraction of time before the arrival of the normal sinus impulse (the impulse originating from a special part of the heart called the "sinus node," which is the normal origin of the electrical impulses that cause the heart to contract and pump blood).

What happens next depends on where the extrasystole originates:

When the normal rhythm is altered because the extrasystolic excitation reaches the "sinus node," the impulse that was already being prepared prematurely is triggered, forcing the sinus node to prepare a new, delayed impulse. As a result, the fundamental sinus rhythm (the true and normal rhythm for any person) will be delayed by an interval, and the pause following the extrasystole is called a "displaced" pause.

If the "extra" beat induces a "refractory phase" (a type of pause), the heart muscle is "incapacitated" from responding to the normal sinus impulse, which is known as a "compensatory pause."

Compensatory pauses follow ventricular extrasystoles, while displaced pauses follow supraventricular extrasystoles (originating from any area above the ventricles).

Regarding the causes of these arrhythmic phenomena, it can be said in general terms that:

Extrasystoles are common in people who are otherwise healthy.
Excessive consumption of coffee, tea, tobacco, calcium, and certain medications can also trigger extrasystoles.
All heart diseases (cardiopathies) can be accompanied by extrasystoles.
Extreme stress or aggression to the nervous system can also cause them.
Exaggerated physical exertion can trigger them.
Extrasystoles often manifest as "irregular palpitations," where the "compensatory pause" is felt as a brief "stoppage" of the heart (a very unpleasant sensation), followed by the post-extrasystolic contraction (the strong "thump" due to prolonged filling of the heart), which may be perceived as a heavy thud in the chest.

Sometimes, a brief sharp sensation may even be felt.

Extrasystoles by themselves are not pathological, unless the person has a history of heart disease. In those cases, it is advisable to conduct a thorough and functional examination of the entire cardiovascular system to determine the origin and need for eventual treatment (such as for heart failure, for example).

The coexistence of high blood pressure does not always have a direct relationship with the cause of extrasystoles.

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