| The two major heart conditions involving rhythm are tachycardia and bradycardia. These are both arrhythmias, also called dysrhythmia.
Arrhythmia means any deviation from a normal rhythm whether it be too fast, too slow or irregular. Irregular heart rates are fairly common and often harmless. They can be regularly irregular or irregularly irregular. Tachycardia is an abnormally rapid hearbeat and can be either regular or irregular. This can be a "normal" condition for some. Atrial flutter is well organized and circulates blood (as opposed to atrial fibrillation in which the atrium pulsates uselessly) with contractions of 250 to 350 per minute. Ventricular flutter is 180 to 250 per minute, is pulseless and quickly progresses to ventricular fibrillation and arrest.
I think that the general term you're looking for is irregular tachycardia. | 
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