Tachykardia

Tachycardia is a heart rate that is faster than normal at rest. In adults, a resting rate above 100 beats per minute is commonly used as the threshold. Tachycardia can reflect a normal physiological response, such as during exercise or excitement, or indicate an underlying medical problem.

Tachycardia encompasses several rhythm disorders with rapid rates but different origins and treatments. Sinus tachycardia arises from a fast but regular impulse from the sinoatrial node and maintains a normal rhythm. Supraventricular tachycardia (SVT) refers to rapid rhythms that originate above the ventricles, usually with a narrow QRS complex. Ventricular tachycardia (VT) begins in the ventricles and often produces a wide QRS complex; VT can be especially dangerous.

Causes vary and include physiologic factors (exercise, fever, pain, anxiety, caffeine), medical conditions (anemia, hyperthyroidism, heart failure, low oxygen, pulmonary embolism, myocardial infarction) and drugs or substances (stimulants, certain bronchodilators, alcohol withdrawal).

Symptoms may include palpitations, lightheadedness, dizziness, chest discomfort, shortness of breath, or fainting; some people have no symptoms. Evaluation relies on electrocardiography (ECG) and clinical assessment, often with telemetry. Distinctions between narrow and wide QRS tachycardias help guide treatment and reveal possible atrioventricular nodal reentrant or ventricular sources. Additional tests may include blood counts, thyroid function, echocardiography, and imaging to assess heart or lung disease.

Management depends on stability and cause. In hemodynamically unstable patients, immediate synchronized cardioversion is indicated. In stable SVT, vagal maneuvers and adenosine are commonly used; if ineffective, rate-controlling medications such as beta-blockers or non-dihydropyridine calcium channel blockers may be given. VT or SVT with structural heart disease may require antiarrhythmic drugs, catheter ablation, or implantation of a defibrillator in selected cases. Treating the underlying condition is essential. Prognosis varies; tachycardias due to benign causes are usually reversible, while malignant forms with heart disease carry higher risk.