The acute phase management of paroxysmal supraventricular tachycardia (PSVT) focuses on promptly terminating the arrhythmia. Clinical intervention is guided by factors such as hemodynamic stability, medical history, and the underlying mechanism of the arrhythmia. Treatment typically progresses in a systematic manner, starting with non-invasive vagus nerve stimulation and advancing to pharmacological interventions. In cases where patients present with hemodynamic instability, synchronized electrical cardioversion may be necessary [14].

5.1.1. Vaginal Nerve Stimulation Treatment

Vagus nerve stimulation is the initial treatment of choice for hemodynamically stable patients due to its simplicity, practicality, and ease of implementation. Successful vagus nerve stimulation techniques have shown efficacy rates ranging from 19% to 54% [15]. 1) Various approaches to vagus nerve stimulation include standard and enhanced Valsalva maneuvers, cold water immersion, carotid sinus massage, pharyngeal cold stimulation, and mechanical stimulation [16]. The Valsalva maneuver, named after the Italian anatomist Valsalva, involves taking a deep breath, closing the glottis, and forcefully exhaling [17]. In the treatment of paroxysmal supraventricular tachycardia (PSVT), patients are instructed to maintain a 45-degree semi-recumbent position and exhale forcefully using a 10mL syringe until the plunger moves for 10 - 15 seconds [18]. 2) Enhanced Valsalva maneuvers entail transitioning to a supine position immediately after exhalation, elevating the legs to 45 - 90 degrees, resting for 15 seconds, and then returning to the semi-recumbent position. Zhao Lu et al. conducted a study involving 2527 PSVT patients to compare the efficacy of modified Valsalva maneuvers with standard Valsalva maneuvers. Their findings revealed a significantly higher success rate with the modified Valsalva maneuver compared to the standard technique [19]. 3) The carotid sinus compression technique involves positioning the patient supine and extending their neck. A medical professional applies pressure to the right carotid sinus using the index and middle fingers for 5 - 10 seconds. If the desired response is not elicited, the opposite carotid sinus should be pressed after 1 - 2 minutes. It is crucial to avoid simultaneous compression of both carotid sinuses to prevent severe complications such as abrupt hypotension or cardiac arrest [1]. During medication use, if symptoms such as dyspnea, bradycardia, or chest pain occur, the drug should be immediately discontinued. It is contraindicated in patients with bronchial stenosis or spasm, second- or third-degree atrioventricular block, and sick sinus syndrome.

5.1.2. Drug Treatment

When the vagus nerve stimulation method is ineffective, drug treatment should be performed under electrocardiogram monitoring. Commonly used drugs are as follows: adenosine (first choice), verapamil, diltiazem, propafone, amiodarone, etc.

Upon binding to the cardiac adenosine A1 receptor, adenosine can activate the acetylcholine-sensitive potassium channel, concurrently inhibiting adenylate cyclase and reducing cAMP levels. This dual mechanism significantly decelerates atrioventricular node conduction and prolongs the effective refractory period, thereby impeding atrioventricular node reentry. Adenosine is the preferred initial pharmacological intervention for paroxysmal supraventricular tachycardia due to its rapid onset, brief half-life, and high efficacy [20]. Typically administered intravenously at doses ranging from 6 mg to 12 mg, it was studied in a cohort led by Nichole Krug, involving 213 patients with PSVT. Among them, 117 individuals (54.9%) received the initial 6 mg dose, while 96 (45.1%) were administered the 12 mg dose. The reversion rates at initial doses of 6 mg and 12 mg were 56.4% and 79.1%, respectively (p < 0.001). Among the 46 patients who did not revert at the initial 6 mg dose, 33 (71.7%) responded after subsequent doses. The emergency department opted for a 12 mg initial adenosine dose over the guideline-recommended 6 mg dose to achieve a higher SVT reversion rate without raising the incidence of adverse reactions [21]. During medication administration, symptoms such as dyspnea, bradycardia, or chest pain warrant immediate discontinuation. This medication is contraindicated in patients with bronchial stenosis or spasm, second- or third-degree atrioventricular block, or sick sinus syndrome.

Verapamil, a non-dihydropyridine calcium channel blocker, selectively inhibits calcium ion channels on cardiomyocyte membranes. This action reduces calcium ion influx, lowers cardiomyocyte excitability and conductivity, extends the effective refractory period of the Atrioventricular node, and ultimately decreases ventricular rate [22]. It is now considered a first-line treatment for paroxysmal supraventricular tachycardia, with an initial recommended intravenous dose of 5 - 10 mg administered slowly over more than 2 minutes. If ineffective after 10 - 15 minutes, a 5 mg dose may be repeated. Verapamil is contraindicated in patients with severe hypotension, second- and third-degree atrioventricular block, and sick sinus syndrome [23][24].

Propafenone, classified as a Class Ic Na+ channel inhibitor, acts by impeding Na+ influx through the Na+ channels on cardiomyocyte membranes. This action results in the deceleration of depolarization, extension of the effective refractory period, elevation of the cardiomyocyte threshold potential, inhibition of Purkinje fibers’ depolarization, reduction of myocardial excitability and automaticity, and slowing of both the response action potential and conduction velocity. Furthermore, Propafenone exhibits β-receptor blocking and calcium channel blocking properties [25][26]. It is recommended as a first-line treatment for paroxysmal supraventricular tachycardia, with an initial dose of 70 mg administered slowly via intravenous injection over 5 - 10 minutes. A repeat dose may be administered after 10 - 20 minutes [27].

Amiodarone, a broad-spectrum antiarrhythmic drug classified as Class I - IV, exerts its main pharmacological effect by non-selectively blocking the potassium channels. This action leads to prolongation of the action potential duration and effective refractory period in the atria, Purkinje fibers, and ventricular myocytes, thereby impeding conduction in the atrioventricular nodes and bypass tracts, consequently slowing the heart rhythm [28]. The recommended initial dose is a slow intravenous injection of 150 mg over 10 minutes. If sinus rhythm is not restored within 20 minutes, a repeat dose may be administered. In comparison to propa-fenone, amiodarone has a slightly delayed onset of action but offers greater safety and a broader spectrum of clinical utility [29].

5.1.3. Emergency Electrical Cardioversion

For patients with refractory drug treatment, hemodynamic instability (systolic blood pressure <90 mmHg), or pre-excitation syndrome (Wolff-Parkinson-White syndrome) accompanied by atrial fibrillation or atrial flutter, the recommended initial energy for biphasic waveform cardioversion is 50 - 100 joules. If the initial attempt is unsuccessful, the energy level can be incrementally increased to 120 joules; for monophasic waveform cardioversion, the energy level is typically set at 100 joules [29]. In a study by Lorenzo Gamberini et al., involving 1234 patients with paroxysmal supraventricular tachycardia (PSVT), the success rate of restoring sinus rhythm using direct current synchronized cardioversion was reported to be 83.9% [30].

Radiofrequency ablation is a sophisticated interventional therapy known for its precise localization and control of the treatment area, minimal invasiveness, rapid recovery, low pain levels, high success rate (exceeding 90% - 95%), minimal complications, and broad applicability. It is currently considered the most efficacious approach for managing paroxysmal supraventricular tachycardia (PSVT) [31][32]. Initially, intracardiac electrophysiological assessment was conducted following puncture of the femoral vein or internal jugular vein under local anesthesia. Subsequently, a mapping electrode catheter was positioned sequentially in the high right atrium (HRA), His bundle (His), coronary sinus (CS), and right ventricle (RV). Tachycardia was provoked through standard procedural stimulation of the high right atrium and right ventricle to ascertain the subtype of paroxysmal supraventricular tachycardia (PSVT) [33]. For patients diagnosed with intraventricular reentrant tachycardia (AVNRT), the slow pathway is typically targeted for ablation through radiofrequency ablation (RFA) or pulsed electric field ablation. A standard 4 mm head catheter is utilized for this procedure. The initial ablation site is situated at the posterior aspect of the Koch triangle and is treated with 15 W power. In cases where there is no evidence of junctional rhythm during ablation, the ablation site will be revisited. Conversely, if a junctional heart rhythm is detected, the power output will be gradually escalated to 20 - 30 W for sustained ablation, with a cumulative duration exceeding 60 seconds. The ablation process is confined to the Koch triangular region. Post-ablation, atrial stimulation is conducted (with or without isoproterenol administration) within 30 minutes of the final ablation to assess the presence of a double pathway phenomenon. Subsequent ablations are performed until AVNRT is no longer inducible [34]. Isoproterenol can simulate a state of sympathetic excitation, which enhances the conduction capacity of the slow pathway and may make residual or damaged slow pathways “reusable.” It also shortens the refractory period of the fast pathway. These two effects collectively create the most favorable conditions for inducing AVNRT. If AVNRT remains non-inducible after isoproterenol administration, with only discontinuous atrioventricular nodal echoes (or even no echoes) observed, the ablation is considered highly thorough, and the risk of postoperative recurrence is extremely low [13]. In patients with atrioventricular reciprocating tachycardia (AVRT), initial evaluation involves right ventricular (RV) stimulation to identify sites of earliest atrial retrograde conduction or ventricular pre-excitation. During ablation procedures, the left accessory pathway (adjacent to the mitral valve annulus) can be accessed retrogradely via the aorta towards the ventricular aspect for lateral ablation, or via the atrial septum pathway for standardization. The right accessory pathway (near the tricuspid valve annulus) can be catheterized directly through the femoral venous route, utilizing support from the SR or RA sheath [35]. Radiofrequency (RF) energy parameters are set at 50˚C - 60˚C, with power outputs of 20 - 40 W for the right pathway and 15 - 30 W for the left pathway. Ablation duration may be prolonged to 60 - 120 seconds per point to ensure efficacy [36]. Ablation success is determined by the disappearance of delta waves, blockage of accessory pathway conduction, and the inability to induce AVRT [37].

The management of paroxysmal supraventricular tachycardia (PSVT) in special populations (such as children and pregnant women) requires particular consideration, as standard treatment regimens may be limited by physiological status, variations in drug metabolism, and potential risks.

As first-line acute management for PSVT, vagal maneuvers constitute the primary intervention for both pediatric and pregnant populations. Should these prove ineffective, pharmacologic treatment (adenosine as the drug of choice) should be initiated. Immediate synchronized cardioversion is warranted upon emergence of hemodynamic instability. For long-term prophylaxis, beta-blockers (such as propranolol) represent the preferred pharmacologic strategy; notably, amiodarone is contraindicated during gestation due to its documented fetal thyrotoxic and neurotoxic potential. Catheter ablation is generally indicated for older pediatric patients (typically exceeding 4 years of age or 15 kg body weight) presenting with recurrent episodes or pharmacotherapy resistance, whereas its implementation should be deferred during pregnancy when feasible [38].