Tachycardias are arrhythmias characterized by an increase in heart rate above 100 beats per minute (bpm), with consequent alteration of hemodynamic efficiency. They may occur in healthy individuals in response to physiological stimuli, such as physical activity or stress, or may be an expression of cardiac or systemic diseases.
Classification
Tachycardias are classified according to their site of origin and pathogenetic mechanism.
SITE OF ORIGIN
Supraventricular tachycardias (SVT): originate in the atria or atrioventricular junction and include sinus tachycardia, atrial tachycardia, atrial flutter, atrial fibrillation and AV nodal or accessory pathway reentrant tachycardia.
Ventricular tachycardias (VT): arise below the bundle of His and can be monomorphic or polymorphic. These include sustained ventricular tachycardia, non-sustained ventricular tachycardia, and ventricular fibrillation.
PATHOPHYSIOLOGICAL MECHANISM
Automatic tachycardias: caused by spontaneous increase in the activity of an ectopic focus, independent of normal regulatory mechanisms.
Reentrant tachycardias: due to abnormal recirculation of the impulse within an electrical circuit, responsible for most paroxysmal tachyarrhythmias.
Triggered activity tachycardias: the result of early or delayed afterdepolarizations, often secondary to ionic dysfunctions or drug intoxication.
Causes and Predisposing Factors
Tachycardias may arise in the absence of structural heart disease or may indicate underlying myocardial alteration. Among the main triggering factors are:
Drugs and substances: sympathomimetics, antiarrhythmics, digitalis toxicity, abuse of alcohol or drugs.
Clinical Manifestations
The clinical picture of tachycardias is extremely variable and depends on the type of arrhythmia, its duration, and the presence of underlying heart disease. The most common symptoms include:
Palpitations: subjective perception of rapid or irregular heartbeats.
Dyspnea and dizziness: consequence of reduced systemic perfusion.
Chest pain: in patients with underlying ischemia, tachycardias may precipitate angina.
Syncope: in cases of critical reduction in cardiac output.
Cardiac arrest: in sustained ventricular tachycardias or ventricular fibrillation.
Diagnosis
The diagnosis of tachycardia is initially based on clinical assessment of the patient, considering medical history, reported symptoms, and predisposing factors. The diagnostic suspicion arises in the presence of palpitations, syncopal episodes, dyspnea or chest pain. In patients with known heart disease, tachycardias may present as clinical worsening or acute heart failure.
The first test to be performed is the resting electrocardiogram (ECG), which allows differentiation between supraventricular and ventricular tachycardias, identifying specific features such as QRS morphology, rhythm regularity, and P waves.
If the baseline ECG does not document tachycardia or if the episodes are paroxysmal, Holter monitoring is performed to record arrhythmias during daily activities. This test is useful to correlate symptoms with arrhythmic episodes and to evaluate their frequency.
In patients whose tachycardia mainly occurs during exertion, the exercise test may be indicated to induce the arrhythmia, assess the hemodynamic response, and identify any signs of myocardial ischemia.
In selected cases, when the diagnosis is unclear or when an ablative treatment is being considered, an electrophysiological study is used. This invasive test allows mapping of arrhythmic circuits, assessment of the mechanisms underlying the onset of tachycardia, and identification of the best therapeutic approach.
Treatment
The treatment of tachycardias depends on the type of arrhythmia and the presence of hemodynamic instability.
Vagal maneuvers: indicated in AV nodal reentrant tachycardias to interrupt the arrhythmic circuit.
Antiarrhythmic drugs: beta-blockers, calcium channel blockers, and class I and III antiarrhythmics according to the underlying mechanism.
Electrical cardioversion: in hemodynamically unstable patients or in dangerous ventricular tachyarrhythmias.
Transcatheter ablation: the procedure of choice for sustained or symptomatic tachycardias, by eliminating the arrhythmic focus.
Implantable cardioverter-defibrillator (ICD): for prevention of sudden death in patients at high risk of malignant ventricular tachyarrhythmias.
Conclusions
Tachycardias represent a broad spectrum of cardiac rhythm disorders that can range from benign manifestations to potentially life-threatening conditions. Correct classification, accurate diagnostic assessment, and targeted treatment are essential to improve the prognosis and quality of life of affected patients.
References
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Priori SG, et al. 2022 ESC Guidelines on ventricular arrhythmias and sudden cardiac death. Eur Heart J. 2022;43(10):802-887.
Zipes DP, et al. Mechanisms, diagnosis, and management of tachyarrhythmias. Circulation. 2021;143(14):e151-e179.
Libby P, et al. Braunwald’s Heart Disease: A Textbook of Cardiovascular Medicine. Elsevier; 2022.
Fuster V, et al. Hurst’s The Heart. McGraw-Hill; 2022.
Papadakis M, et al. Genetic predisposition and clinical management of ventricular tachycardia. Nat Rev Cardiol. 2021;18(7):412-425.
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Antzelevitch C, et al. Pathophysiology and treatment of reentrant tachycardias. J Cardiovasc Electrophysiol. 2020;31(8):2017-2032.
