Which arrhythmia is characterized by a rapid, uncontrolled contraction of the atria?

Atrial fibrillation is characterized by a rapid, uncontrolled contraction of the atria. In this arrhythmia, there is chaotic electrical activity in the atria, leading to ineffective atrial contractions. This results in an irregular and often rapid heart rate as the atrial activity does not coordinate effectively with the ventricular response.

In atrial fibrillation, the loss of coordinated atrial contraction can lead to stagnant blood flow in the atria, increasing the risk of thrombus formation and subsequent stroke. It is often associated with symptoms such as palpitations, fatigue, and shortness of breath, which vary depending on the rate of ventricular response and the presence of underlying heart disease.

Other arrhythmias mentioned, such as ventricular tachycardia and ventricular fibrillation, primarily originate from the ventricles and involve different mechanisms and clinical implications. Supraventricular tachycardia refers to a fast rhythm originating above the ventricles, but it doesn't specifically describe the atrial contraction dynamics seen in atrial fibrillation. Thus, the defining characteristics and clinical impact of atrial fibrillation make it the answer for this question.