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4.2 Increased automatist of the ectopic pacemaker 4.2.1 Atrial, junctional, idioventricular rhythms
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4.2 Increased automatist of the ectopic pacemaker 4.2.1 Atrial, junctional, idioventricular rhythms

An ectopic pacemaker or ectopic focus is an excitable group of cells that causes a premature heart beat outside the normally functioning of the human heart. Acute occurrence is usually non-life threatening, but chronic occurrence can progress into tachycardia and bradycardia. In a normal heart beat rhythm the SA node usually suppresses the ectopic pacemaker activity due to the higher impulse rate of the SA node. However, if there is a malfunctioning SA node its inactivity allows the ectopic pacemakers to generate their rhythm.

An ectopic pacemaker can reside within a part of the conduction system of the heart, or within the muscle cells of the atria or ventricles. When an ectopic pacemaker initiates a beat, premature contraction occurs. A premature contraction will not follow the normal signal transduction pathway, and can render the heart refractory or incapable of transmitting the normal signal from the SA node. Location of the pacemaker can also change its affect on the SA node and its rhythm. An ectopic pacemaker located in the atria is known as an atrial pacemaker and can cause the atrial contraction to be faster. However, a pacemaker near the AV node and the septum is known as a junctional pacemaker. The pacemaker that is operating in the ventricles is known as the ventricular.

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Figure 21 — Ectopic atrial rhythm

ECG signs of atrial rhythm:

Regular rhythm.

Heart rate is more slowly than 60 bpm in common.

P wave is usually inverted.

PQ interval is shorter than 0.12 seconds.

Normal QRS duration and shape.

T wave with normal size and configuration.

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Figure 22 — Accelerated junctional rhythm

ECG signs of junctional rhythm:

Regular rhythm.

Heart rate may vary considerably.

P wave  is inverted, absent or appears after QRS complex.

QRS duration is usually within normal limits, though may be slightly prolonged.

T wave is usually within normal limits.

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Figure 23 — Idioventricular rhythm

ECG signs of idioventricular rhythm:

Regular rhythm.

Heart rate is usually nearly 20 to 40 bpm.

P wave is absent.

QRS complex wide and bizarre configuration, duration exceeds 0.12 seconds.

T wave is abnormal, its deflection usually occurs in the opposite direction from that of the QRS complex.

QT interval is usually prolonged.



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