What term is used to describe the rapid, ineffective contractions of a heart chamber that are more coordinated than fibrillation?

The correct term for the rapid, ineffective contractions of a heart chamber that are more coordinated than fibrillation is flutter. In a flutter, the atria or ventricles contract rapidly but in a more organized manner compared to fibrillation, where contractions are chaotic and uncoordinated.

Atrial flutter, for example, is characterized by a distinct and regular rhythm, often with a "sawtooth" pattern on the electrocardiogram (ECG). This condition can still lead to inefficient blood pumping but typically maintains some degree of coordination among its contractions, distinguishing it from the disorganized rhythm seen in fibrillation.

Bradycardia refers to a slower than normal heart rate, which does not involve the rapid contractions described in the question. Tachycardia indicates a faster heart rate but does not necessarily mean the contractions are ineffective or disorganized. Asystole describes a complete lack of heart electrical activity, meaning no contractions occur, which is clearly different from what is described in the question. Thus, flutter is the term that accurately captures the essence of rapid, yet somewhat coordinated, contractions in this context.