Junctional rhythm describes an abnormal

heart rhythm The cardiac conduction system (CCS) (also called the electrical conduction system of the heart) transmits the signals generated by the sinoatrial node – the heart's pacemaker, to cause the heart muscle to contract, and pump blood through the ...

resulting from impulses coming from a locus of tissue in the area of the

atrioventricular node The atrioventricular node or AV node electrically connects the heart's atria and ventricles to coordinate beating in the top of the heart; it is part of the electrical conduction system of the heart. The AV node lies at the lower back section of t ...

(AV node), the "junction" between atria and ventricles. Under normal conditions, the heart's

sinoatrial node The sinoatrial node (also known as the sinuatrial node, SA node or sinus node) is an oval shaped region of special cardiac muscle in the upper back wall of the right atrium made up of cells known as pacemaker cells. The sinus node is approximat ...

(SA node) determines the rate by which the organ beats – in other words, it is the heart's "pacemaker". The electrical activity of

sinus rhythm A sinus rhythm is any cardiac rhythm in which depolarisation of the cardiac muscle begins at the sinus node. It is characterised by the presence of correctly oriented P waves on the electrocardiogram (ECG). Sinus rhythm is necessary, but not s ...

originates in the sinoatrial node and depolarizes the atria. Current then passes from the atria through the atrioventricular node and into the

bundle of His The bundle of His (BH) or His bundle (HB) ( "hiss"Medical Terminology for Health Professions, Spiral bound Version'. Cengage Learning; 2016. . pp. 129–.) is a collection of heart muscle cells specialized for electrical conduction. As part of t ...

, from which it travels along

Purkinje fibers The Purkinje fibers (; often incorrectly ; Purkinje tissue or subendocardial branches) are located in the inner ventricular walls of the heart, just beneath the endocardium in a space called the subendocardium. The Purkinje fibers are specia ...

to reach and depolarize the ventricles. This sinus rhythm is important because it ensures that the heart's atria reliably contract before the ventricles. In junctional rhythm, however, the sinoatrial node does not control the heart's rhythm – this can happen in the case of a block in conduction somewhere along the pathway described above, or in sick sinus syndrome, or many other situations. When this happens, the heart's

can take over as the pacemaker, starting the electrical signal that causes the heart to beat.Depending on where the rhythm originates in the AV node, the atria can contract before ventricular contraction due to retrograde conduction, during ventricular contraction, or after ventricular contraction. If there is a blockage between the AV node and the SA node, the atria may not contract at all. Junctional rhythm can be diagnosed by looking at an

ECG Electrocardiography is the process of producing an electrocardiogram (ECG or EKG), a recording of the heart's electrical activity. It is an electrogram of the heart which is a graph of voltage versus time of the electrical activity of the hear ...

: it usually presents without a P wave or with an inverted P wave. Retrograde, or inverted, P waves refers to the depolarization from the AV node back towards the SA node.

Epidemiology

Junctional rhythm is seen equally in men and women, and can be seen intermittently in young children and athletes, especially during sleep. It occurs commonly in patients with sinus node dysfunction. 1/600 cardiology patients over the age of 65 have sinus node dysfunction.

Causes

Anything that impairs the SA node can potentially lead to a junctional rhythm. Some examples below: *

Chest trauma A chest injury, also known as chest trauma, is any form of physical injury to the chest including the ribs, heart and lungs. Chest injuries account for 25% of all deaths from traumatic injury. Typically chest injuries are caused by blunt mechanism ...

* Ischemic heart disease *

Sick sinus syndrome Sinus node dysfunction (SND), also known as sick sinus syndrome (SSS), is a group of abnormal heart rhythms ( arrhythmias) usually caused by a malfunction of the sinus node, the heart's primary pacemaker. Tachycardia-bradycardia syndrome is a varia ...

Myocarditis Myocarditis, also known as inflammatory cardiomyopathy, is an acquired cardiomyopathy due to inflammation of the heart muscle. Symptoms can include shortness of breath, chest pain, decreased ability to exercise, and an irregular heartbeat. The ...

* Hypothyroidism *

Hyperkalemia Hyperkalemia is an elevated level of potassium (K+) in the blood. Normal potassium levels are between 3.5 and 5.0mmol/L (3.5 and 5.0mEq/L) with levels above 5.5mmol/L defined as hyperkalemia. Typically hyperkalemia does not cause symptoms. Occasi ...

Muscular dystrophy Muscular dystrophies (MD) are a genetically and clinically heterogeneous group of rare neuromuscular diseases that cause progressive weakness and breakdown of skeletal muscles over time. The disorders differ as to which muscles are primarily affe ...

* Certain medications * Other neuromuscular disorders

Clinical presentation

The presentation and symptoms a patient can present with are varied and often dependent on the underlying cause of the junctional rhythm. Patient's can be

asymptomatic In medicine, any disease is classified asymptomatic if a patient tests as carrier for a disease or infection but experiences no symptoms. Whenever a medical condition fails to show noticeable symptoms after a diagnosis it might be considered asy ...

for example, or experience difficulty breathing and chest pain if they have underlying

congestive heart failure Heart failure (HF), also known as congestive heart failure (CHF), is a syndrome, a group of signs and symptoms caused by an impairment of the heart's blood pumping function. Symptoms typically include shortness of breath, excessive fatigue, a ...

. Other nonspecific findings include dizziness, fatigue,

palpitations Palpitations are perceived abnormalities of the heartbeat characterized by awareness of cardiac muscle contractions in the chest, which is further characterized by the hard, fast and/or irregular beatings of the heart. Symptoms include a rapi ...

, and passing out. This diagnosis is made via ECG.

ECG findings

The first finding is that junctional rhythms are regular rhythms. This means that the time interval between beats stays constant. The next normal finding is a normal QRS. Since the impulse still travels down the bundle of His, the QRS will not be wide. Junctional rhythms can present with either bradycardia, a normal heart rate, or

tachycardia Tachycardia, also called tachyarrhythmia, is a heart rate that exceeds the normal resting rate. In general, a resting heart rate over 100 beats per minute is accepted as tachycardia in adults. Heart rates above the resting rate may be normal (su ...

. The most obvious abnormal finding will be abnormal P waves. One of three options can occur: 1. There are no P waves. This is because of either failure of retrograde flow to the atria or the P wave is hidden in the QRS. If the P wave is hidden that implies the atria depolarize at the same time as the ventricles. 2. There are inverted P waves prior to the QRS complex. This is because of retrograde flow to the atria causing depolarization prior to the ventricular contraction. Since the depolarization is occurring in the opposite direction, the P wave deflection is inverted. 3. There are inverted P waves after the QRS complex. This is because of retrograde flow to the atria after ventricular contraction.

Classes of junctional rhythms

Junctional bradycardia

Junctional bradycardia is a rhythm that still originates in the AV node or bundle of His, but simply beats at a rate less than 40 beats per minute.

Junctional escape rhythm

Junctional escape rhythm is a rhythm that still originates in the AV node or bundle of His, but beats at the intrinsic automaticity of the AV node, between 40 and 60 beats per minute.

Accelerated junctional rhythm

Accelerated junctional rhythm is when the rhythm of emerged impulses is more than 40 to 60 beats per minute, which is the natural range of the junction. It happens in some instances such as digoxin toxicity, and usually has a rate of between 60 and 100 bpm.

Junctional tachycardia

Junctional tachycardia Junctional tachycardia is a form of supraventricular tachycardia characterized by involvement of the AV node. It can be contrasted to atrial tachycardia. It is a tachycardia associated with the generation of impulses in a focus in the region of ...

is a rhythm that still originates in the AV node or bundle of His, but simply beats at a rate above 100 beats per minute.

References

{{Heart diseases Cardiac arrhythmia