OVERVIEW
The incidence of atrioventricular refractory tachycardia (AVRT) is second only to atrioventricular nodal refractory tachycardia (AVNRT), accounting for about 30% of all supraventricular tachycardias. Patients may experience palpitations, precordial discomfort or angina, dizziness, and in severe cases, lowered blood pressure, shock, and cardiac insufficiency.
Etiology
The prevalence of AVRT with occult bypass involvement is unknown. Patients with AVRT with occult bypass involvement occur from children to the elderly and are somewhat more common in younger individuals. Younger patients often do not have organic heart disease, and older patients may have a variety of organic heart disease. Most patients with preexcitation syndrome with AVRT have no clinical basis for organic heart disease, and a small percentage of patients may have hypertrophic cardiomyopathy and rheumatic heart disease.
Symptoms
1. Pre-excitation type atrioventricular tachycardia
AVRT has an early onset, with palpitations, precordial discomfort or angina pectoris, dizziness, and in severe cases, lowered blood pressure, shock, and cardiac insufficiency.The heart rate during AVRT episodes may be slightly faster than that of AVNRT, but it is mostly in the same range. The heart rhythm is absolutely regular and the heart sounds are equal in intensity. During tachycardia, due to atrial dilatation and increased secretion of antidiuretic sodium excretory factor, polyuria may occur after the termination of tachycardia. Generally speaking, if the heart rate exceeds 160 beats/minute, palpitation and chest tightness will be felt, and if the heart rate exceeds 200 beats/minute, there will be a drop in blood pressure, dizziness and even fainting.
2. Retrograde atrioventricular tachycardia
Clinical symptoms and clinical process are more serious and dangerous than anterograde atrioventricular tachycardia. The heart rate is 140-250 beats/minute at the onset of the tachycardia, and is often around 200 beats/minute. A heart rate of 150 beats per minute or more produces significant symptoms and hemodynamic disturbances. It is often complicated by angina pectoris, cardiogenic shock or syncope. In severe cases, it can lead to ventricular arrhythmia and even sudden death.
Examination
1. Electrocardiography
(1) Examination of anterograde atrioventricular tachycardia ① Heart rate 150-240 beats/minute, mostly ≥200 beats/minute, sudden stop. ② The atrial P′ wave at the beginning of the P′ wave is different from the P′ wave morphology during tachycardia. It is also definitely different from the sinus P wave. (iii) Timely spontaneous or electrical stimulation of atrial or ventricular pre-systole can induce and terminate the attack. ④ QRS wave electrical alternans may occur in some patients. ⑤ The P′-R interval of the heart beat (atrial pre-systole) that initiates the tachycardia episode is not abruptly prolonged, suggesting that AVRT does not require the involvement of AV node dual channels. (vi) Excitation of the vagus nerve (e.g., using carotid artery compression) terminates tachycardia. (7) Functional bundle branch block is easily seen at the onset of a tachycardia episode. If the bundle branch block occurs on the same side of the bypass, the R-R interval is prolonged by more than 30 ms; if the bundle branch block occurs on the opposite side of the bypass, the R-R interval remains unchanged. (8) Normal QRS waveforms may be present in the same episode, as well as QRS waveforms with bundle-branch block. The atria, ventricles, atrioventricular conduction system, and bypass are necessary parts of the foldback loop, and a 1:1 atrioventricular relationship is always maintained during an episode of tachycardia. If there is more than second-degree atrioventricular block, AVRT can be definitely excluded when there is a missed beat.xi In those with anterograde AVRT due to dominant preexcitation bypass, the δ-wave disappears during the onset of the tachycardia, and when there is no onset of the tachycardia, it presents the typical preexcitation syndrome, with short P-R intervals, wide QRS waveforms, and δ-waves.
(2) Examination of retrograde atrioventricular refractory tachycardia (1) The heart rate is 150-250 beats/minute, mostly around 200 beats/minute. Absolutely neat. ② Retrograde P′ wave appears after the QRS wave and is located in the first half of the R-R interval. (iii) Wide aberrant QRS waves show a complete preexcitation pattern for >0.12s, mostly around 0.14s. Wide QRS wave tachycardia is presented. ④ Timely electrical stimulation can induce and terminate the attack. ⑤The use of vagal excitation such as carotid artery compression can terminate the tachycardia.
(3) Examination of multiple atrioventricular bypass tachycardias (1) In sinus rhythm, atrial excitation is transmitted down to the ventricle through different bypasses, causing changes in the electrical axis and different patterns. In cases of multiple atrioventricular bypass circuits, when pre-transmission and retrograde atrioventricular tachycardia occur alternately, the cardiac cycle is inconsistent due to changes in the refractory pathway.
2. Electrophysiologic examination
(1) Examination of anterograde atrioventricular tachycardia (1) The induced atrial pre-stimulus does not have a jumping prolongation of the SR (with the exception of the combined AV node double pathway), and as long as the critical prolongation of the SR causes the impulse to reach the ventricular end of the bypass pathway at the same time that the latter is out of the retrograde effective refractory period, then refractory can be formed. The frequency of paroxysmal episodes is fast: obvious retrograde P′ waves can be seen on the ST-T or T wave, and R-P<P-R, indicating that ventriculoatrial conduction is faster than atrial conduction, and the R-P interval in the esophageal leads is ≥70 MS. ③ The polarity of the P′ wave in each lead reflects the location of the atrium to which the bypass is attached, for example, the bypass of the left free wall has a P′ wave in Ⅰ and AVL leads, and the parapaplacental and posterior septal bypasses have a P′ wave in Ⅱ and Ⅲ leads, P′ waves in AVF leads. ④Patients with paroxysmal seizures often have functional block of the ipsilateral bundle branch of the bypass, which is due to the fast atrioventricular conduction, the refractory period is shorter than the effective refractory period of the ipsilateral bundle branch, so the impulse of the retrograde transmission to the atrium must be bypassed to the downward transmission of the contralateral bundle branch before reaching the ventricular end of the bypass, which results in prolongation of refractory loop, increase of the refractory time, slowing down of the heart rate, and prolongation of R-P intervals. In the case of bundle branch block on the same side of the bypass, the V-A interval is prolonged by more than 25 MS compared with that in the absence of block. ⑤ Atrial pre-systolic stimulation of downward conduction can terminate the episode because the atria are an integral part of the refractory loop, so well-timed atrial pre-systolic stimulation can block refractoriness. (6) Episodes of tachycardia are often accompanied by alternating QRS waves and/or alternating lengths of the cardiac cycle, and this narrow QRS tachycardia with QRS alternans is highly specific (96%) for the determination of OAVRT. (7) The earliest atrial depolarization in the sequence of eccentric reverse atrial excitation occurs in the atria near the bypass. The earliest sequence of eccentric reverse atrial excitation was the recording of an A wave of atrial excitation in the right auricle adjacent to the bypass, followed by the recording of an A wave on the Hitchcock’s bundle, and finally the recording of an A wave at the coronary sinus orifice.
(2) Examination of reverse atrioventricular tachycardia ① Ventricular excitation is eccentric with the same QRS wave morphology as when atrial pacing results in maximal preexcitation. ② Atrial and ventricular waves are conducted 1:1. (iii) Tachycardia can be terminated when ventricular preexcitation fails to excite the Hirschsprung’s bundle or the atria. (4) The sequence of atrial excitation is the same in ventricular pacing and tachycardia. ⑤ Generally, when the critical distance between the single bypass and the normal atrioventricular conduction system is more than 4 cm: it is easy to form a retrograde refractory tachycardia. (6) Sequence of retrograde atrial excitation: excitation is transmitted symmetrically from the AV node to the right and left atria in a retrograde fashion. (7) In a typical retrograde atrioventricular tachycardia, the Hippocampal bundle is always depolarized first, and then the retrograde excitation of the atria continues. Therefore, the H wave always precedes the A wave. (8) The tachycardia may be induced or terminated by an appropriate presynchronous electrical stimulus. ⑨ AAVRT can also usually be terminated by atrioventricular block. ⑩ The electrophysiologic basis of AAVRT is the relatively short cis- and retrograde-effective response periods of the bypass and the atrioventricular conduction system, which, together with the delayed conduction of well-timed preperiodic contractions in the atrioventricular system, results in the onset of AAVRT.
(3) Examination of multiple atrioventricular bypass refractory tachycardia (1) Folding between bypass and bypass; (2) Folding between Kent’s bundle and Mahaim’s bundle; and (3) Folding at the end of Mahaim’s bundle or between junctional ventricular bypass and atrial bundle bypass.
Diagnosis
Mainly rely on electrocardiogram and cardiac electrophysiologic examination.
Complications
Atrioventricular tachycardia occurs in patients with organic heart disease, or in patients with reverse atrioventricular tachycardia. Due to the fast ventricular rate and long duration, it can be combined with syncope, angina pectoris, cardiogenic shock, hypotension, and induce heart failure, and in severe cases, sudden death can occur.
Treatment
For those who have frequent episodes with long duration and obvious symptoms, it is necessary to prevent the episodes after termination.
1. Drug prevention
All the drugs that can control the acute attack, in principle, can prevent recurrence, but the prevention of recurrence is far less effective than the control of acute attacks. Commonly used drugs include digoxin, verapamil, β-blockers, amiodarone, propafenone (cardioplegia) and so on.
2. Catheter ablation
At present, catheter ablation has achieved very good results in the treatment of this disease, which is the method of its eradication and should be the first choice of treatment.
Prognosis
There is no clear relationship between this disease and organic heart disease, and it often occurs suddenly after physical or mental exertion or stress. As long as the duration is not long, the heart rate is less than 200 beats/minute, and there is no serious hemodynamic disorder in general, and the attack can be controlled by appropriate medication, radiofrequency ablation can be the radical treatment, and the prognosis is good. However, if the original cardiac organic disease, the heart rate of 200 beats/minute during the attack, the attack duration is too long, can also appear blood pressure drop, fainting and heart failure symptoms, the prognosis is worse, should be actively treated, control the recurrence of radiofrequency ablation as soon as possible.
Prevention
1. Chronic patients during treatment
Pharmacologic therapy may control recurrence by directly acting on the refractory ring or by inhibiting triggers, such as spontaneous pre-systole. Indications for pharmacologic therapy include patients who have frequent episodes that interfere with normal life or who have severe symptoms and are unwilling or unable to undergo catheter-based radiofrequency ablation therapy. Patients with episodic, short-lived, or mild symptoms can be treated without medication, or given medication when needed for tachycardia episodes.
2. Inhibitory effect of drugs on refractoriness
The inhibitory effect of drugs on refractoriness can be counteracted by sympathetic excitation, and the effect of drugs nearly disappears during physical activity and anxiety. Therefore, in daily life and work, avoiding mental tension or excessive fatigue, regular life, regular living, optimism, emotional stability can reduce the recurrence of this disease.