Paroxysmal supraventricular tachycardia is a rapid and uniform heart rhythm that occurs in bursts, referred to as supraventricular tachycardia, and is relatively common. The human heartbeat is initiated by the heart’s automatic pacing points and is not controlled by the brain. The automatic pacing points of the heart proceed from top to bottom: sinus node, atrioventricular node, atrioventricular junction, left and right bundle branches, and Purkinje’s fibers. When the upper level is unable to perform the pacing function, it is initiated by the lower level. A heart beat that is normally generated by impulse commands from the sinus node is called sinus rhythm. Any heartbeat other than this is abnormal. In contrast, tachycardia generated by impulses emanating from above the atrioventricular junction is called supraventricular tachycardia, which is pathological and requires prompt treatment. The division of supraventricular tachycardia in the Department of Internal Medicine of the Utopia County People’s Hospital Qiao Liang is divided into four types of supraventricular tachycardia: atrioventricular nodal tachycardia, cis-atrial tachycardia, intra-atrial tachycardia, and inappropriate sinus tachycardia.
Pathogenesis of supraventricular tachycardia
The pathogenesis is mostly folding, and in a small percentage of atrial arrhythmias the pathogenesis is either increased autoregulation or a trigger mechanism. Foldback excitation can occur between the sinoatrial node and atria, within the atria, within the AV node, and between the atria and ventricles. The latter two types of proximal regression account for more than 90% of supraventricular tachycardias and are a common arrhythmia in the emergency setting. The first two types of regression, and increased autoregulation, account for less than 10% of cases and are not extremely frequent or persistent, and do not often prompt patients to seek emergency medical care.
The clinical features are sudden onset and abrupt cessation. During an attack, symptoms include palpitations, chest tightness, anxiety, and dizziness. Rarely, syncope, angina pectoris, heart failure and shock are seen. Patients feel that their heart is beating very fast, as if it is about to jump out, and it is very uncomfortable. The heart rate at the onset is 150 to 250 beats per minute and lasts for seconds, minutes or hours and days.
Electrocardiographic features.
(1) Regular rhythm with equal RR spacing and a frequency of 150-250 beats per minute.
(2) The QRS is supraventricular and maintains a sinus rhythm shape.
(3) ST-segment depression and T-wave inversion are common.
P waves in leads II, III, and aVF that are upright and in front of the QRS wave group suggest atrial tachycardia. P waves in leads II, III, and aVF that are inverted and immediately after the QRS wave group suggest atrioventricular nodal fold or atrioventricular tachycardia. The absence of P waves is a characteristic feature of atrioventricular tachycardia with intra-atrial node folding.
(5) The onset is abrupt, usually triggered by an atrial precontraction with a significantly prolonged downstream PR interval, which subsequently causes a tachycardia episode.
Measures to terminate episodes of supraventricular tachycardia.
1. Stimulation of the vagus nerve
This method is simple, easy to perform, and often the first to be used. Among them, carotid sinus compression and lack of sava (Valsava) maneuvers are more effective. Compression of the eyeball may lead to retinal detachment, and is now less commonly used.
(1) When compressing the carotid sinus, the patient is placed in a recumbent or semi-recumbent position to avoid syncope. Finger pressure is applied at approximately the same level as the superior border of the thyroid cartilage where the carotid pulsation is most pronounced. First press the right side, if it is not effective, then press the left side after a few minutes, but not both sides at the same time. Each compression should not be longer than 5s, and cardiac monitoring should be performed, and the heart rate should be stopped as soon as it slows down. This method is contraindicated in people over 75 years of age who have had cerebrovascular lesions. Compression of the carotid sinus alters the intravascular pressure, and the message of elevated pressure is transmitted to the cardiac inhibitory center, reflexively enhancing vagal tone.
(2) The Valsava maneuver is more effective. The patient is instructed to take a deep breath in and hold it, then exhale forcefully, or exhale deeply and hold it, then inhale forcefully, repeatedly.
(3) Compress the tongue root with tongue depressor (chopstick, spoon) to induce nausea and vomiting action.
(4) Compress the eye. The patient lies on his back, closes his eyes and looks down, and the family member presses above one eye with his thumb, gradually increasing the pressure for 10 seconds each time, taking turns to press both sides of the eye. Compression should not be too long and should not be too hard. Stop compression as soon as the supraventricular velocity slows down. Glaucoma and high myopia are not allowed to use this method.
2.Pressure-raising drugs
The blood pressure can be increased reflexively by the drugs to increase the vagal tone. It should be noted that blood pressure drugs can only be used for those without cardiovascular or cerebrovascular disease. Generally when the systolic blood pressure rises to 21.3kPa (160mmHg) the tachycardia can often be terminated, the pressure should not be too high. The available antihypertensive drugs are Methocarbamol (not more than 15mg at a time), Alamine, dobutamine, norepinephrine and phenylephrine (5mg dissolved in 50ml of saline and injected slowly intravenously to raise blood pressure to 4.0-5.3kPa). Antihypertensive drugs can also be used with antiarrhythmic drugs to improve the efficacy.
3.Anti-arrhythmic drugs
For supraventricular tachycardia with narrow QRS wave groups and hemodynamic stability, isoparathy is the most effective drug, which can terminate 95% of episodes. The first intravenous dose is 5-10mg (0.1mg/kg body weight). The initial 5mg can be pushed in slightly faster, and subsequent doses should be advanced at a rate of 1mg/min. Most of the episodes are effective within 2-3 min, if not, repeat 5-10 mg after 15 min. monitor the heart rhythm during the pushing process, and stop the injection if the tachycardia is terminated. Excessive doses of isoparatide and too fast a push may cause severe sinus arrest, atrioventricular block, and a decrease in blood pressure. Verapamil should not be used in patients with pre-existing hypotension, but it can be used in combination when the tachycardia is not terminated after boosting the blood pressure, often resulting in rapid tachycardia arrest. In patients with mild cardiac dysfunction and normal blood pressure, verapamil is not contraindicated, because the rapid termination of the attack is beneficial to the recovery of cardiac function.
Cetiran 0.4-0.6 mg, or insulin 0.1-0.15 mg/kg body weight intravenously (1 mg/min rate) can terminate the tachycardia, or slow down the ventricular rate.
Cardioplegia is an effective drug used clinically in recent years, which can be dissolved in 70mg in glucose solution and pushed slowly into the vein within 5min. In case of ineffectiveness, the injection can be repeated after 20-30 min. If necessary, a third 70mg can be injected. cardioplegia has a short half-reduction period without accumulation and is relatively safe, but it has the side effect of causing ventricular arrhythmia.
The efficiency of acetamidofurone 5mg/kg by slow intravenous infusion is about 50% in terminating tachycardia. However, long-term oral administration is effective in preventing recurrence.
Adenosine triphosphate 20mg rapid intravenous injection can rapidly terminate the attack, and its efficiency is the same as that of verapamil. However, this drug has many side effects, such as decreased blood pressure, sinus bradycardia, and ectopic ventricular beats. Fortunately, the half-reduction period of this drug is very short, and the side effects disappear quickly.
4. Electrophysiological methods
Transesophageal left atrial pacing is a simple method and can be widely used. An electrode catheter is inserted through the patient’s nostril. In adults, the insertion depth is 35-40 cm, and the site with the highest atrial wave amplitude on the esophageal electrogram is selected for programmed stimulation to easily capture the atria and achieve the therapeutic goal. The program stimulation voltage is 20～40V and pulse width is 10ms.
5.Transcatheter radiofrequency ablation can effectively eradicate paroxysmal supraventricular tachycardia.