Disturbances in Heart Rhythm

Bradycardia occurs when the heart rate falls below 60 beats per minute, while tachycardia is a heart rate above 100 beats per minute. Both represent disturbances in heart rhythm. Bradycardia may cause insufficient blood flow, whereas tachycardia can lead to inadequate ventricular pumping and low blood pressure.

Atrial fibrillation causes unsynchronized electrical activity in the atria, producing irregularly spaced QRS complexes and ill-defined P waves on an ECG. Ventricular fibrillation creates chaotic electrical signals causing ventricles to quiver rather than contract, producing grossly abnormal waves and stopping blood pumping entirely, resulting in circulatory failure.

Heart block occurs when electrical pathways between the atria and ventricles are blocked. First-degree block extends P-Q intervals on an ECG. Second-degree block shows fewer QRS complexes. Third-degree or complete block reduces ventricular beating to less than 40 beats per minute, severely impairing cardiac function.

In ventricular tachycardia, the heart beats too fast and the ventricles fail to pump sufficient blood. This results in low blood pressure and potential heart failure. The rapid, uncoordinated beating prevents adequate blood circulation throughout the body, compromising oxygen delivery to tissues.

Arrhythmias result from defects in the heart's conduction system. Triggers include stress, caffeine, alcohol, nicotine, cocaine, certain medications, congenital defects, diseases, and electrolyte abnormalities. These factors disrupt normal electrical activity, causing irregular, too-fast, or too-slow heartbeats that affect cardiac output.

Severe arrhythmias like ventricular fibrillation require immediate cardiopulmonary resuscitation and defibrillation, where a strong electrical current stops the fibrillation. High-risk patients may receive an automatic implantable cardioverter defibrillator that monitors rhythm and delivers corrective shocks. Automated external defibrillators are available in emergency settings.

Different arrhythmias produce distinct ECG patterns. Atrial fibrillation shows irregularly spaced QRS complexes and ill-defined P waves. Ventricular fibrillation displays grossly abnormal waves and complexes. Heart block shows extended P-Q intervals in first-degree block and fewer QRS complexes in second-degree block, helping clinicians identify the specific rhythm disturbance.