OVERVIEW
Lown, Ganong, and Levine reported in 1952 a normal QRS graphic electrocardiographic presentation presenting short P-R intervals (<0.12 seconds) and absence of delta waves. It may be accompanied by paroxysmal supraventricular tachycardia or atrial flutter, atrial fibrillation with rapid ventricular rate, so it is called short P-R syndrome, also known as James bundle preexcitation syndrome or LGL syndrome.
Etiology
Most patients with short P-R syndrome do not have organic heart disease, while a few patients have sinus node lesions, mitral valve disease, mitral valve prolapse and cardiomyopathy.
The anatomical basis of short P-R syndrome is the presence of James bypass (also known as AV node bypass), which is a part of the fibers of the posterior interjunctional bundle that bypasses the top of the AV node and stops at the lower part of the AV node or atrioventricular fasciculus, and thus shortens the P-R interval and does not enter the ventricle directly, resulting in the absence of δ waves, normal QRS wave timing, and providing the basis for the folding back, so it may be complicated with AV node folding back tachycardia or tachycardia. Therefore, it can be complicated by atrioventricular nodal tachycardia or rapid atrial fibrillation or atrial flutter. However, in recent years there has been disagreement as to where the James bundle begins and ends, or even whether it actually exists.
Symptoms
Patients with short P-R syndrome without arrhythmia may have no clinical symptoms. Patients with short P-R syndrome with arrhythmia have clinical symptoms and hemodynamic changes, such as palpitations, chest tightness, shortness of breath, dizziness, and syncope, depending on the type of arrhythmia and the clinical background of the cardiovascular disease. Short P-R syndrome is easily combined with paroxysmal supraventricular tachycardia (AVNRT, etc.), the incidence of which is lower than that of WPW syndrome combined with supraventricular tachycardia, accounting for only 50% or less, with a rapid frequency of more than 200 beats/minute and a regular rhythm. Some patients may present with atrial flutter or atrial fibrillation.
Examination
1. Electrocardiography
(1) Typical electrocardiogram of short P-R syndrome ① P-R interval <0.12 seconds. ①P-R interval <0.12 seconds. ②Normal QRS wave, no δ wave. ③Shortening of P-J interval. ④ No secondary ST-T changes.
(2) Typical electrocardiographic features of short P-R syndrome ① Short P-R syndrome is mainly a shortening of conduction time in the AV node, so the P-R interval is <0.12 seconds, but most of them are 0.08-0.11 seconds. Sometimes the P wave widens and even enters the QRS wave, so that the P-R interval disappears. (ii) A P-R interval of <0.12 seconds is not unique to the short P-R syndrome. It has been noted that some unexplained atrial fibrillation is due to intermittent short P-R syndrome.
(3) Special types of short P-R syndrome electrocardiograms ① Occult short P-R syndrome: It has been suggested that about 50% of the patients with short P-R syndrome are usually in an insidious state and only appear momentarily under certain circumstances, such as the stimulation of atrial pre-systole and atropine test. ② Frequency-dependent short P-R syndrome: its characteristics are the same as frequency-dependent WPW syndrome. (iii) James’ fasciculus intermedius phenomenon: similar to Kent’s fasciculus intermedius cycle. Short P-R syndrome with arrhythmia: short P-R syndrome itself can be accompanied by arrhythmia.
2. Characteristics of electrophysiologic examination
(1) Hippocampal bundle electrographic characteristics Short P-R syndrome, that is, interatrial short circuit, should be characterized by shortening of atrial conduction time, most of which is caused by accelerated conduction in the AV node, which is called accelerated AV node conduction, and its intra-atrial and Hippocampal system conduction is normal. the A-H interval is often less than 60 ms.
(2) Atrial pacing test The Hippocampus electrogram alone often does not clearly reveal the characteristics of short P-R syndrome. The diagnosis can be further clarified with the help of atrial pacing, as well as certain drug reactions.
3. Pre-periodic stimulation of the atrial program
This is very similar to the atrial incremental pacing stimulus response. The most common is a mild lengthening of the A-H interval as the paired intervals (A1-A2) of the atrial pre-stimulation shorten. There were more AV node double pathway responses than in atrial pacing stimulation, especially when the basal stimulus perimeters (S1-S1 and A1-A1) were shorter, because a shorter basal perimeter would result in a longer AV node refractory period, which would easily reveal the electrophysiologic phenomenon of AV node double pathway.A1-A2 gradually shortened when A2-H2 gradually lengthened, forming a gentle curve. Sometimes there may be a jumping phenomenon, suggesting that there is a curve of double pathway in the AV node.
In atrial programmed prephase stimulation, especially when the basal circumference is short, the presence of an atrioventricular-Hispanic bundle bypass is suggested by the short and unchanging A-H and H-V intervals during the stimulation process. Because the bypass is normal myocardium, and the short basal circumference results in a short duration of refractory period, prephase stimulation does not prolong the conduction time. If atrial stimulation elicits a marked prolongation of A2-H2 when the cardiac cycle of the underlying rhythm is short, the short circuit is within the AV node (accelerated fibers or attachments within the AV node).
4. Drug reactions
Propranolol slows AV node conduction but has no effect on the bypass or atrial myocardium. The prolongation of A-H after intravenous propranolol suggests that the short circuits are in tissue within or attached to the AV node.
5. Comparison of Measurements of Effective Atrioventricular Nodal Response Time
In patients with a history of supraventricular tachycardia associated with short P-R intervals (P-R < 0.12 seconds), the AV nodal effective response time was slightly shorter than that of patients with normal P-R intervals, but the difference was not significant. In patients with a history of supraventricular tachycardia who have accelerated AV nodal conduction, the AV nodal effective refractory period is shorter than in patients with normal P-R intervals and a history of supraventricular tachycardia.
6. Atrioventricular conduction
Measurement of atrioventricular conduction, or AV reversal time, in the short P-R syndrome shows that patients with accelerated AV nodal conduction have good AV conduction, and that there is no significant difference in AV reversal time with or without dual pathways, or with or without concomitant supraventricular tachycardia. The majority of patients with atrioventricular-Hirschsprung’s bundle bypass do not have atrioventricular conduction, and the few who do have atrioventricular conduction have poorer conduction than atrioventricular anterograde conduction.
Clinically, it is often found that some patients with ECG P-R interval ≤0.12 seconds and history of paroxysmal supraventricular tachycardia are not very certain, and cannot be diagnosed as LGI syndrome, in which case electrophysiologic examination should be performed.
Diagnosis
The electrophysiologic basis for the diagnosis of short P-R syndrome mainly includes: ① Hippocampal bundle electrogram with A-H interval <60 ms and normal H-V interval. ② P-R (or A-H) interval increment <100 ms during atrial pacing. (iii) Atrial pacing rate of 200 beats/minute is maintained at 1:1 downbeat. ④ ECG P-R interval ≤ 0.12 seconds.
Treatment
Treatment of preexcitation syndrome without complications: For those who are found to have preexcitation syndrome on physical examination ECG but no complications occur, no treatment is needed, but follow-up observation is required.
Treatment of preexcitation syndrome combined with tachyarrhythmia:
1.Pharmacologic treatment during the episode
Tachyarrhythmias due to the presence of ventricular preexcitation, especially in symptomatic cases with frequent episodes of hemodynamic changes, should be treated immediately with pharmacologic therapy.
Electrocardiography should be preferred in patients who are hemodynamically in poor condition (with severe hypotension, etc.) or in those who are well and whose arrhythmic tachycardia is rapid and prolonged (unless there is no device available for cardiac cardioverter or there are contraindications to cardiac cardioverter). Pharmacologic therapy should be tried first if the hemodynamic situation is good and the arrhythmic tachycardia is tolerable. Drugs that prolong the atrioventricular bypass and inhibit its conduction function should be used.
(1) Propafenone is often the drug of choice. It should be diluted with 20 ml of 5% dextrose solution and then slowly injected intravenously. If it is ineffective, it can be repeated after 15 to 20 minutes. In most patients, 70 to 140 mg is effective. The following two points should be noted when using propafenone (cardioplegia): In a small number of patients, the ventricular rate may increase with the drug, thus worsening the arrhythmia. This may be related to the fact that the drug delays intra-atrial conduction, slows the atrial rate, and results in 1:1 conduction in the AV node or bypass. For example, 2:1 conduction before the use of the drug, the use of the drug due to the slowing down of the atrial rate leads to 1:1 conduction, the ventricular rate doubled; propafenone (cardioplegia) has an inhibitory effect on the myocardial contractility, especially the dose is large or cardiac function is poor, can be in the resumption of the cardiac rhythm after the occurrence of a state of low blood pressure. If you can strictly grasp the indications, the drug is safe and effective.
(2) Procainamide Some people advocate as the drug of choice, dissolved in 40 ml of liquid (5% dextrose), intravenous slow push, high efficiency. Procainamide can significantly prolong the bypass forward effective response period, can moderately prolong the reverse effective response period and significantly prolong the P-A interval.
(3) Amiodarone Termination of preexcitation syndrome combined with acute episodes of atrial fibrillation or atrial flutter, high efficiency. Diluted with 5% dextrose solution or saline 20 ml and slowly pushed intravenously. If it is ineffective after 10-15 minutes, it can be repeated once, not exceeding the total amount of 9mg/kg. Increased ventricular rate and low blood pressure may aggravate myocardial ischemia and induce ventricular tachycardia or ventricular fibrillation, so it should be alerted.
(4) Other drugs: Flecainide, quinidine, lidocaine, β-blockers, digitalis preparations (cediran), verapamil (isobarbital) should be contraindicated.
2. Treatment of interictal period
For the pre-excitation syndrome combined with tachycardia attacks less frequent, short duration, symptoms are not obvious and can be self-recovery of the intermittent patients, can not be treated. However, overwork and other triggering factors should be avoided. If atrial pre-systole, ventricular pre-systole, etc. occurs, it should be corrected by taking propafenone (cardioplegia), mesylate (slow heart rhythm), etc., which can reduce the number of tachycardia episodes.
For intermittent patients with preexcitation syndrome combined with frequent episodes of tachycardia, maintenance doses of the above therapeutically effective drugs should be taken for a long period of time to prevent recurrence, and effective prophylactic drugs can also be screened by cardiac electrophysiologic examination of induced arrhythmias.
In the intermittent period, in patients with frequent episodes, a radical approach should be used. Currently, radiofrequency ablation is mostly used.
3. Synchronized direct current cardioversion
Electrical cardioversion (power 100-200J) is effective in terminating atrioventricular tachycardia and preexcitation syndrome combined with atrial fibrillation, and it is especially suitable when the latter is difficult to identify with ventricular tachycardia due to the widening and distortion of the QRS wave in the electrocardiogram caused by preexcitation and the difficulty in choosing drugs, as well as when there are obvious hemodynamic obstacles due to the tachyarrhythmia. After reentry, drugs are still required for maintenance.
4. Surgical treatment of preexcitation syndrome
Before catheter-based radiofrequency ablation was carried out, surgical treatment of preexcitation syndrome by cutting off or injecting with anhydrous alcohol or local freezing bypass achieved good efficacy and high cure rate. However, the surgical method is difficult to be widely used due to high trauma and has been replaced by catheter radiofrequency ablation. Only in some special cases, such as congenital heart disease with preexcitation syndrome or acquired heart disease requiring surgery. Surgery can be considered as a concomitant treatment for pre-excitation syndrome.
5. Catheter-based radiofrequency ablation for pre-excitation syndrome
Catheter radiofrequency ablation is a safe procedure that uses low-energy radiofrequency current through the catheter. As it has no obvious thermal damage to myocardium brought by direct current shock, does not need general anesthesia, does not produce air pressure injury, generally does not lead to myocardial penetration, and seldom induces arrhythmia, it can issue radiofrequency current for many times and in many parts of the body to ablate, and the patients do not have any feeling and pain.
6. Implantable cardioverter-defibrillator
Implantable cardioverter-defibrillator can be considered when drug treatment is ineffective or catheter radiofrequency ablation fails.