Overview
When agitation in the sinus node or atria fails to reach the atrioventricular (AV) junction region on time, and its interval exceeds the time limit of the autonomic cycle of the potential pacing site in the junction region, the potential pacing site issues an impulse, which causes an ectopic beat known as a junctional fugitive beat. Three or more consecutive zonal escape beats constitute a zonal escape rhythm.
Causes
1. Common causes of junctional escape beats
(1) Sinus node hypoplasia is mainly sinus bradycardia. When the frequency of sinus rhythm is lower than that of the junction zone, junction zone escape beats can occur. Acute myocardial infarction, especially the lower wall infarction, in the early stage of the onset of some patients occur in the junction area escape beat. It also occurs in patients with cardiomyopathy and myocarditis.
(2) Sinus arrest After a long sinus arrest, a junctional escape beat may occur. This is seen in myocarditis, after shock resuscitation, and the effects of certain drugs.
(3) Sinus block such as myocarditis, myocardial infarction, digitalis intoxication.
(4) Atrioventricular block is mainly seen in third-degree and second-degree atrioventricular block.
(5) Atrial pre-systole followed by temporary inhibition of the sinus node.
(6) Ventricular pre-systole with retrograde conduction to the atrium Atrioventricular junction escape beats and escape rhythms are most common in middle-aged and elderly people, and are rarely seen in children.
2. Common causes of junctional escape rhythms
Junctional fugitive rhythms are uncommon and mostly temporary. It is mainly secondary to sinus atrial block, sinus arrest, marked and very slow sinus bradycardia and atrioventricular block.
This rhythm can also be caused by digitalis intoxication, quinidine intoxication, or by the application of beta-blockers, reserpine, etc., or by the early effects of atropine. However, it is common in people with heart disease. It can also be seen in cardiomyopathy, acute myocardial infarction with sinus bradycardia, conduction block, degenerative changes in the intraventricular conduction system. This type of arrhythmia may also occur in patients undergoing cardiac surgery, electrolyte disorders, and so on. Longer-lasting torsades de pointes arrhythmias are associated with significant sinus node dysfunction.
Symptoms
1. Split-beat arrhythmias
Symptoms are usually caused by underlying heart disease and sick sinus node syndrome, sinus bradycardia, sinus block, sinus arrest, atrioventricular block, etc. The symptoms are not obvious. Escape beats themselves have no obvious symptoms.
2. Split rhythm
Splice rhythms do not cause significant hemodynamic disturbances. Most of the patients have symptoms caused by primary heart disease, such as palpitations and shortness of breath. For example, palpitations, shortness of breath, etc. Physical examination shows a heart rate of 40 to 60 beats per minute and no significant change in the intensity of the first heart sound. In the case of bradycardia, the heart rate is <40 beats per minute, and symptoms such as dizziness, palpitations, and syncope may occur.
Examination
1. Electrocardiographic characteristics of a transitional escape beat
(1) QRS waves appearing after longer intermittent cardiac cycles: their shape and time frame are supraventricular.
(2) P-wave is invisible in most of the transitional zone escape beats: in a few cases, a retrograde P-wave can be seen before and after the QRS wave. The P wave is inverted in leads II, III, and aVF, and upright in leads aVR and V1. The retrograde P wave may appear before the QRS wave (P-R interval <0.12s), or after the QRS wave (R-P interval <0.20s), or buried in the QRS wave.
(3) If several crossing zone escape beats occur, the period of each escape beat is fixed.
(4) Sometimes sinus P waves may appear before or after the QRS waves. However, the P-R interval is <0.10s.
2. Special types of atrioventricular junction zone escape beats
(1) Accelerated junction zone escape beats and junction zone escape beat hypofunction Accelerated junction zone escape beats occur under the same conditions as the above escape beats, but the period of their occurrence is shorter than 1.0 s, or even less than 0.7 s. This suggests that the myocardial atrioventricular (AV) junction zone tissue has abnormally high autoregulation at that time. On the contrary, there were cases in which myocardial atrioventricular pacing did not occur until the sinus pause reached more than 4.0 s, or even after a longer pause without pacing. This suggests that the atrioventricular interface pacing function is abnormally weak or inhibited.
(2) Bradyarrhythmic atrioventricular transition zone escape beats with an escape period of >1.50 s and a frequency of <40 beats per minute.
(3) Fugitive-recapture dichotomy Also known as pseudo-recurrent rhythm. Most commonly seen in sinus block. Electrocardiographic features: each intersegmental zone escape beat is immediately followed by a sinus beat. This type of agitation captures the P-QRS-T wave of the ventricle and the P wave is sinus. It is mostly seen as a result of a P-P phase that is too long and exceeds the sum of the duration of the escape beat and the period of inactivity following the escape beat.
Diagnosis
The diagnosis can be made on the basis of etiology, clinical manifestations and ECG.
Treatment
1. There is no special treatment for the transitional zone fugitive rhythm per se, mainly for the underlying heart disease.
2. A too-slow escape rhythm can lead to obvious hemodynamic disorders, and may even lead to A.S. syndrome, syncope, etc., and make it difficult to control heart failure. When the escape rate is too slow, atropine or isoprenaline can be used to increase the ventricular rate. If necessary, the installation of permanent pacemaker treatment can be considered.
3. Drug intoxication should be stopped immediately.
4. If the treatment of third-degree atrioventricular block is ineffective, a pacemaker should be placed.
Prognosis
Cross-zone escape rhythms are a physiologic cardioprotective mechanism. Its clinical significance depends on the underlying cardiac disease. Transient zonal escape rhythms are generally considered to be clinically insignificant, whereas persistent zonal escape rhythms are often indicative of myocardial damage. The occurrence of third-degree atrioventricular block or sinus arrest, sinus block, on the one hand, suggests that the underlying heart disease is serious, on the other hand, suggests that the prognosis is poor. Those with occasional sinus bradycardia have a better prognosis.