Junctional Rhythm Arrhythmia
What is Sinus Rhythm? The sinoatrial node or SA node is the heart’s natural pacemaker to control the rate of the heart beats. First of all the electrical activity for setting up of normal rhythm originates in the sinoatrial node. A wave of depolarization is first sent to the atria. From the atria the stimulus after words travels to the bundle of His, from the atria. The wave of depolarization then travels to ventricles through the Purkinje fibers and ventricles are thus depolarized in the end. This is the normal rhythm of the heart and is called as Sinus Rhythm. Heart’s atria always contract before the ventricles under the control of SA node.
What is Junctional Rhythm However, it happens in some cases that the Sinoatrial node stops its control over the heart’s rhythm and its place is taken over by the Atrioventricular node (AV node) situated at the junction of atria and ventricles. The rhythm of heart in such cases is known as Junctional Rhythm. This can happen due to a block in normal conduction pathway. When the heart’s atrioventricular node takes over as the pacemaker the atria will still contract before the ventricles; but through a retrograde conduction sent by the ventricles. The conduction comes from the AV node into ventricles, and then from ventricles into the atria. The conduction then travels which through both the chambers of atria.
ECG of Junctional Arrhythmia Since the junctional rhythms are abnormal kind of heart beats these are also known as Junctional Arrhythmia. Junctional rhythms are diagnosed by looking at an ECG or EKG. The tracings of ECG arrhythmia are very peculiar in such cases. The EKG may exhibit an absence of a P wave or an inverted P wave. Occasionally it may happen that the P wave is shown as a retrograde, i.e. it appears after the QRS complex.
This in fact is an escape mechanism which happens when the AV node starts acting as the natural pacemaker due to its intrinsic automaticity. This generally happens only over a period of time. The function of depolarizing the myocardium (walls of the heart) is taken over by the AV node only during the period of significant sinus bradycardia or total heart block.
ECG in such cases would show a narrow QRS complex, with a rate of 40-60 beats per minute. Junctional rhythm, higher than 60 beats per minute may be present just after taking over from a clinically serious bradycardia.
Junctional rhythms are also present in patients with sick sinus syndrome. The patient may or may not show symptoms during a junctional rhythm. Symptoms may occur after a subsequent contraction after the closing of the tricuspid valve.
Other Causes for Junctional Arrhythmia Other than the sick sinus syndrome junctional arrhythmia is also found in the following cases:
- Digoxin toxicity
- Ischemia of the AV node
- After cardiac surgery
- Acute inflammatory processes
- Influence of certain drugs like calcium blockers and beta-blockers
- Influence of antiarrhythmic agents)
- Due to increased adrenergic tone in some of the metabolic states
- Isoproterenol infusion
Why do the junctional Rhythms Occur? Junctional rhythm mechanism are in no way associated with the mortality of the patient. Mortality actually results from the sick sinus syndrome or the heart block. The junctional rhythm is a kind escape mechanism to act as a “backup” or escape mechanism during the bradycardia. Since the junctional escape rhythm has a rate greater than the sinus rhythm it acts as a safety mechanism. Prominent jugular venous pulsations may occur due to the right atrium contracting with a clogged tricuspid valve.
These rhythms occur with more or less the same frequency in male and female populations.
Junctional escape rhythms are also common in athletic individuals or young individuals during periods of increased vagal tone. (Vegal tone is the measure of variability in the rate of heart beat during inspiration and expiration.)