Supraventricular tachycardia: definition, diagnosis, treatment, and prognosis
Supraventricular tachycardia involves an acceleration of the heart rate in the structures of the heart that lie above the ventricles, giving rise to arrhythmias
Tachycardia (supraventricular and nonventricular) is a rhythm disorder characterized by an acceleration of the heart rate
Tachycardia is defined as an episode with a heart rate generally exceeding 120 beats per minute (bpm).
The term supra-ventricular is given to all those rhythm disturbances associated with acceleration of heart movements (hyperkinetic arrhythmias) originating from the part of the heart above the ventricles.
Supraventricular tachycardias are divided into re-entry forms and those of increased automatism (TSV)
Under normal conditions, the heartbeat originates as an electrical impulse from the sinoatrial node (a structure located in the right atrium that functions as a pacer or pacemaker), propagates in the atria, and reaches the atrio-ventricular node, an electrical communication pathway between the atria and ventricles.
From the atrio-ventricular node, the electrical impulse passes to the His bundle, a conduction system formed by specialized cardiac cells that transmit the impulse to the two ventricles.
Paroxysmal supraventricular re-entry tachycardia occurs most frequently in episodic form, hence the term paroxysmal.
The term reentry indicates that a pulse that travels through a cardiac structure in a certain direction comes back to reactivate the tissue from which it came.
In supraventricular tachyarrhythmias from increased automatism, the cells normally charged with mechanical activity (cardiac muscle contraction) take on properties of step-marker cells and discharge automatically at a rate higher than that of the atrial sinus, the physiological step-marker.
Automatic supraventricular tachycardia can occur in isolation or associated with heart disease.
The symptomatology of paroxysmal supraventricular tachycardia in the newborn is insidious and often difficult to pinpoint, so that tachycardia is often recognized only when it reveals itself with an obvious picture of heart failure.
In the older child, on the other hand, subjective symptomatology is ‘communicated’ and can range from fleeting palpitation to more long-lasting palpitation that may be associated with sudden weakness, difficulty standing up straight, dizziness, and syncope.
Supraventricular tachycardia from re-entry or increased automatism can be diagnosed by performing the following clinical and instrumental assessments:
- The baseline electrocardiogram, which in cases of tachycardia may record a very high rate (180-340 beats per minute);
- The 24-hour dynamic electrocardiogram according to Holter for recording paroxysms;
- The treadmill ergometer test: although it rarely determines the triggering of tachycardia, it can be useful;
- Echocardiogram is necessary to unveil any associated morpho-functional diseases.
In cases where it is deemed necessary, transesophageal electrophysiologic study, by means of probes introduced into the esophagus, at the level of the heart, or endocavitary, with stimulation and recording of electrical activity from within the heart by means of thin catheters introduced through the blood vessels, may be performed.
Therapy is based on research and treatment of the underlying disease condition, use of antiarrhythmic drugs, or transcatheter ablation surgery.
Acute therapy of paroxysmal supraventricular reentry tachycardias, in cases of severe decompensation and/or cardiogenic shock, is synchronized external electrical cardioversion or transesophageal atrial pacing.
Instead, in the case of heart failure, you can start with vagal maneuvers that aim to stimulate the vagus nerve
The most commonly used are carotid artery massage, pressure on the closed eyes and pressure exerted on the abdomen.
In neonatal age, the most effective is diving reflex (application of an ice pack to the baby’s face for a few seconds), which can be repeated several times.
If vagal maneuvers fail, the drug of first choice is adenosine, as a rapid bolus, followed by rapid infusion of saline.
In all reentry paroxysmal supraventricular tachycardias, it is recommended to take antiarrhythmic drugs for relapse prevention.
Transcatheter ablation is performed in any case of refractoriness to antiarrhythmic therapy and is preferred when the patient reaches 30 kg body weight.
It is an interventional procedure that aims to inactivate the structures from which the arrhythmia originates.
Once the probes are introduced inside the heart, a careful electrophysiological study is first performed, which aims to identify with great accuracy the area from which the arrhythmia originates (mapping).
The responsible area, once identified, is scarred with a heat-generating current.
It is not possible to completely prevent tachycardia initiation considering the natural and physiological causes of tachycardia initiation.
In patients with paroxysmal supraventricular tachycardia from abnormal pathway re-entry, antiarrhythmic therapy may be discontinued after the first 8-12 months of life by verifying by electrophysiological studies whether tachycardia can still be provoked.
If tachycardia can still be provoked, consideration should be given to resuming treatment.
Spontaneous resolution may occur in 30% to 50% of cases in the first year of life.
In other periods of life, definitive disappearance of supraventricular reentry tachycardias is difficult while for automatic ones it occurs in 30 to 40% of cases.