Paroxysmal Supraventricular Tachycardia
Paroxysmal supraventricular tachycardia is an arrhythmia characterized by electrical activity with supraventricular origin (atrial or junctional), regular rhythm and frequency between 120 and 250 beats / minute. Paroxysmal supraventricular tachycardia episodes started and ended suddenly, lasting seconds, minutes, hours or days and may be repeated at intervals of hours, days or months.
- In children: congenital heart disease (interatrial septal defect, ventricular septal defect, atrioventricular septal defect, patent ductus arteriosus, tetralogy of Fallot) ventricular preexcitation syndrome, open heart surgery.
- In young adults: on the healthy heart (75% of cases), viral myocarditis, preexcitation syndrome;
- Older adults: coronary heart disease, dilated cardiomyopathy;
- Iatrogenic: prosthetic valve, coronary bypass, digoxin, chemotherapy.
Paroxysmal supraventricular tachycardia pathogenesis:
Most case of paroxysmal supraventricular tachycardia (70-90%) are caused by reentry mechanisms, the substrate of these mechanisms is the existence of functional differences in the driving of cardiac structures or the presence of an accessory bundle.
Depending on the location of the reentry circuit, are described the following forms of paroxysmal supraventricular tachycardia:
- Paroxysmal supraventricular tachycardia with atrioventricular node reentry , making a circular motion.
- Paroxysmal supraventricular tachycardia with reentry at atrioventricular level. Reentry occurs at the level of a macrocircuit including atrioventricular node (where impulse is driven anterograde) and an accessory atrioventricular bundle (where impulse is conducted retrograde). It also called reciprocal tachycardia.
- Paroxysmal supraventricular tachycardia through sinus node.
- Paroxysmal supraventricular tachycardia by atrial reentry, occurs when exist a longitudinal dissociation of interatrial Bachmann fascicle .
Other rare forms of paroxysmal supraventricular tachycardia (10-30%) occur with increasing ectopic automatism or with triggered activity: ectopic atrial tachycardia, multifocal atrial tachycardia, junctional ectopic tachycardia.
Paroxysmal supraventricular tachycardia diagnosis is placed on symptoms, physical examination and on ECG interpretation.
Clinical manifestations are similar in all forms of paroxysmal supraventricular tachycardia: accesses starts suddenly with the feeling of strike in the chest, palpitations rapid and regular, anxiety, dyspnea, episodes of angina pectoris. Faintness or syncope may be present at the beginning or at the end of paroxysmal supraventricular tachycardia crisis. After the access patients have cold sweats and polyuria. Heart sounds are tachycardic, heart rate is 120-250 beats / minute and regular. The pulse is regular and accelerated. Sometimes are present hypotension, signs of heart failure and signs of cardiogenic shock.
ECG reveal the following: regular rhythm frequency of 120-250 beats / minute, negative P wave in leads DII, DIII and aVF, positive in aVR, P waves may be located before or after the QRS complex, but most often are integrated into the QRS complex, as a cause of simultaneous atrial and ventricular activation. Atrioventricular driving is 1 / 1. QRS complex, has generally a normal appearance but may have a longer duration than normal if is associated with organic or functional bundle branch block.
The end paroxysmal supraventricular tachycardia access is done suddenly and spontaneously after vagal stimulation maneuvers.
Treatment of paroxysmal supraventricular tachycardia access include the following measures:
- Vagal stimulation maneuvers: Sino-carotidean massage and Valsalva maneuver (expiration with closed glottis) may interrupt the paroxysmal supraventricular tachycardia access in 80% of cases. They are contraindicated in patients who have hypotension.
- Pharmacological treatment is indicated in case of failure of the previous maneuvers and includes the following:
- Adenosine (6-12 mg, intravenously) and verapamil (2.5 to 10 mg, intravenously) are drugs of first choice due to short acting-time and lower risk of side effects.
- Beta blockers (esmelol, propranolol, administered intravenously) are the second line of therapy because can stop the access of paroxysmal supraventricular tachycardia or can reduce its frequency.
- Digoxin (intravenous) is not preferred in emergency situations, because its effect is installing slower.
- Electric Conversion:
- Electrical atrial or ventricular stimulation with high frequency (overdrive) is recommended when the drug therapy failed, in patients with recurrence of paroxysmal supraventricular tachycardia and in patients who need electrical conversion and were previously treated with digoxin.
- External electric shock is necessary in the presence of signs of hemodynamic deterioration or in presence of obvious signs of myocardial ischemia. External electric shock is administered synchronized on the QRS complex to prevent ventricular fibrillation.
Paroxysmal supraventricular tachycardia recurrence prevention is done by administering beta blockers, verapamil, diltiazem or administration of antiarrhythmics drugs from class IA and class IC.
In the case of paroxysmal supraventricular tachycardia accesses with increased frequency and severity, is indicated ablation through radiofrequency current.