The heart contracts thanks to specialised cellular structures that generate electrical impulses and regulate their distribution within the heart.
Under normal circumstances the electrical impulse originates in the sinoatrial node, travels through the atria and reaches the atrioventricular node, which is the only pathway for electrical communication between the atria and ventricles; from here the impulse travels to the bundle of His and the intraventricular conduction system.
In some people, the atrioventricular node has abnormal functional structure. Such people have two different conduction pathways (fast and slow) with different conduction velocity characteristics.
In common nodal tachycardia, one pathway conducts quickly but has a longer recovery time after activation (refractoriness); the other conducts more slowly but recovers faster.
In some conditions, these functional characteristics mean that a single electrical impulse reaching the atrioventricular node can perform multiple recirculations, rising and falling within the NAV (nodal re-entry).
Patients with this type of tachycardia complain of palpitations of varying duration and frequency.