Overview.
Sinus-node refractory tachycardia (SNRT), also known as sinus node refractory tachycardia, is a condition in which refractory excitation occurs within the sinus node and between its adjacent atrial tissues, especially in patients with sinus node lesions. The disease can be seen at any age, with a prevalence between 40 and 60 years of age. It is common in the elderly and is more common in men. Tachycardia episodes are paroxysmal, i.e., they occur suddenly and terminate abruptly, and the duration of each episode varies.
Etiology
Mostly occurs in older patients with organic heart disease. It is common in patients with sick sinus node syndrome and coronary artery disease, but also in cardiomyopathy, rheumatic heart disease, hypertensive heart disease, congenital heart disease, pulmonary heart disease and so on.
Symptoms
The disease can be seen at any age, with a prevalence between 40 and 60 years of age. It is common in the elderly, and men are more common, accounting for about 60%. Tachycardia episodes are paroxysmal, i.e., they occur suddenly and terminate abruptly, and the duration of each episode varies from a few seconds to a few hours, with an average of 130 beats/min. Most of the patients are accompanied by palpitations, shortness of breath, chest tightness, and dizziness. Only a few may be accompanied by hemodynamic disorders. Tachycardia is often triggered by emotional excitement, stress, exercise, etc., and in some cases there is no obvious trigger. The frequency of episodes may increase from year to year, and the duration of episodes tends to lengthen with the course of the disease.
Examination
1. Electrocardiography
Typical electrocardiographic manifestations: ① tachycardia consisting of more than 3 consecutive sinus pre-systoles: frequency of 100-160 beats/min, the average of 130 beats/min. ② P′ wave morphology is the same as or similar to the normal sinus P-wave. ③The length of the P′-R interval is related to the frequency of the tachycardia. However, it is usually greater than 0.12 s and less than 0.20 s. ④ The R-P′ interval > P′-R interval. ⑤ The P′-P′ interval may be suddenly prolonged before the termination of the tachycardia. (6) The ventricular rate may be regular or irregular. (7) The tachycardia is paroxysmal. (8) Atrial pre-systole can induce and terminate tachycardia.
2. Electrophysiologic examination
(1) Timely atrial stimulation can induce and terminate tachycardia.
(2) There can be a clear, wide evoked window.
(3) Tachycardia can be induced and terminated by repeated repetitions.
(4) Vagal stimulation may terminate the tachycardia.
(5) Tachycardia is induced independently of atrioventricular or intra-atrial conduction delay.
Diagnosis
(1) The diagnosis can be confirmed by the sudden onset of the attack and the typical electrocardiogram during the attack;
(2) If the attack is short-lived and difficult to capture on the surface ECG, Holre examination can be relied upon;
(3) If the diagnosis is difficult, noninvasive esophageal electrophysiology can be performed first;
(4) Intracardiac electrophysiologic examination has the value of definite diagnosis.
Differential diagnosis
1. Sinus tachycardia with increased autoregulation
(1) SNRT is usually the result of a lesion in the sinus node, whereas sinus tachycardia is a physiologic response. It may also be a reflection of some pathologic state, but the sinus node is normal.
(2) SNRT is sudden onset and abrupt termination, and most episodes are short in duration. Sinus tachycardia often occurs gradually and stops gradually, without the characteristics of sudden onset and sudden termination, and the duration is also long. Up to a few hours, a few days or longer.
(3) SNRT esophageal atrial pacing program stimulation can be induced and terminated, while sinus tachycardia can not be induced and terminated.
(4) SNRT can be terminated or its frequency significantly slowed by stimulation of the vagus nerve, whereas sinus tachycardia can only be temporarily slowed but not abruptly terminated.
2.Non-paroxysmal sinus tachycardia
Non-paroxysmal sinus tachycardia is a serious and persistent sinus tachycardia, which is characterized by faster heart rate, long duration, poor drug response, and often leads to tachycardia cardiomyopathy.
3. Intra-atrial refractory tachycardia (IART)
(1) The relative atrial stress during IART results in slow intra-atrial conduction, whereas there is no intra-atrial conduction delay otherwise seen during sinus refractoriness in SNRT.
(2) The atrial echo during IART is distinctly different from the sinus P wave.
(3) The sequence of atrial excitation was seen to be different from the sinus P wave during intracardiac electrogram recording.
(4) Changing the site of right atrial stimulation during IART often cannot be repeated, while stimulation of different atrial sites can repeatedly induce sinus refractoriness.
4. Autonomic atrial tachycardia (AAT)
Autonomic atrial tachycardia is characterized by sudden onset and offset, but the frequency of the onset is faster, and the morphology of the atrial P-wave is significantly more variable than that of the sinus P-wave.
5. Fast-slow type atrioventricular nodal refractory tachycardia
In the latter type, the R-P interval > P-R interval during the onset of tachycardia, but the P′ wave is retrogradely transmitted from the ventricle to the atrium, so the P-wave direction before and after the onset of tachycardia is reversed. P′ wave inversion in II, III, and aVF leads can be distinguished from SNRT.
Treatment
1. Drug therapy
(1) β-blockers Oral preparations are usually sufficient. For example: propranolol (cardioplegia) orally; atenolol (amiloride); metoprolol (betalactam). β-blockers have a better therapeutic effect on a part of the patients, long-term use of β-blockers, can not be suddenly stopped, should be gradually reduced to maintain in order to stop the drug.
(2) Calcium antagonists (verapamil), digitalis, amiodarone and other drugs have stable efficacy in most patients ① verapamil (isobarbital); ② digoxin; ③ amiodarone orally, and reduce the dosage after the tachycardia is controlled.
(3) Adenosine Adenosine is ineffective in terminating other types of atrial tachycardia. Its mechanism is not clear.
2. Non-pharmacologic treatment
Radiofrequency ablation can cure SNRT.
Prognosis
The prognosis is usually good.
Prevention
1. Avoiding mental stress and overwork, regular life, regular living, optimism and emotional stability can reduce the recurrence of the disease.
2. Avoid spicy and stimulating food; quit smoking, alcohol and coffee; eat light food.