When this happens, The heart's sinoatrial node establishes the rate by which the heart beats. Sinoatrial node is the heart’s pacemaker. In junctional rhythm, sinoatrial node does not control the pace at which heart beats. Causes of this vary but most commonly, there is a block in conduction somewhere along the pathway that starts from heart’s sinoatrial node end ends in the ventricles.
The electrical activity of sinus pace starts in the sinoatrial node and depolarizes the atria. Current then passes from the atria through the AV node, also known as atrioventricular node from which it moves along Purkinje fibers to arrive at and depolarize the ventricles. This sinus pace is vital for the reason that it guarantees that the heart's atria reliably contract before the ventricles.
If this happens, the heart's atrioventricular node starts acting as a pacemaker. It has intrinsic automaticity that makes it possible to initiate and depolarize the myocardium for the period of significant sinus bradycardia or total heart block. It is an escape mechanism, which produces a narrow QRS complex, with a rate of 40-60 beats per minute. An accelerated junctional rhythm, in which the rate is higher than 60 beats per minute, is a narrow complex rhythm that often takes over from a clinically bradycardic sinus node pace.
Frequency and Outcome
Junctional rhythms are most commonly found in patients with sick sinus syndrome or severe bradycardia in which AV nodal region may determine the heart pace. Depending on the heart rate during a junctional rhythm, patient may have symptoms or not. Symptoms may occur because of a trial conduction and subsequent contraction when the tricuspid valve is closed. Stages of junctional rhythm are not always connected with increased mortality rate. Mortality may result from the hearth block or sick sinus syndrome, and not the junctional pace mechanism. This mechanism serves as a "backup pace" during the periods of bradycardia.
Junctional escape rhythms are more common in in younger and/or athletic individuals during periods of increased vagal tone. They occur equally in male and female population, and at any age.
In some cases, predominant junctional rhythm is caused by structural heart disease or/and a sick sinus syndrome, during which the junctional escape rhythm supersedes the sinus rate and provides a safety mechanism. Prominent jugular venous pulsations may occur due to the right atrium contracting with a clogged tricuspid valve.
Reasons for which this take place involve sick sinus syndrome (including drug-induced), digoxin toxicity, ischemia of the AV node, a cutely after cardiac surgery, acute inflammatory processes, diphtheria, from certain drugs (for example, beta-blockers, calcium blockers, most antiarrhythmic agents), metabolic states with increased adrenergic tone, isoproterenol infusion.