Premature activation of ventricular myocardium from an ectopic focus is

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Premature activation of ventricular myocardium from an ectopic focus describes a premature ventricular contraction. It means the ventricle fires an impulse early from an abnormal focus within the ventricular muscle, outside the normal conduction pathway. On an ECG this shows up as a wide, strange-looking QRS complex that occurs earlier than expected and usually without a preceding P wave, often followed by a pause as the rhythm resets. This is distinct from a premature atrial contraction, which starts in the atria and typically has a premature P wave with a normal-appearing QRS; a junctional rhythm, which paces from the AV node and usually produces a narrow QRS with P waves that may be inverted or absent; and sinus tachycardia, which is a faster-than-normal rhythm arising from the SA node with a normal P-QRS-T sequence. So the described phrase precisely defines a ventricular ectopic beat that activates the ventricle prematurely.