![]() Additionally many arrhythmias, particularly in the ventricles, can lead to cardiac arrest. Multiple small re-entry loops can occur in the atria, leading to atrial fibrillation.Īrrhythmias are particularly dangerous as they allow blood to collect in the heart chamber and form clots, leading to an increased risk of strokes or MIs. When the conduction damage is incomplete, it allows the impulse to spread the wrong way through the damaged area and create a circle of excitation. Re-entry loop: This occurs when the normal spread of excitation across the heart is disrupted due to a damaged area.After-Depolarisations: This is when abnormal depolarisations follow the action potential – thought to be caused by high intracellular Ca 2+.Latent pacemaker regions can become activated due to ischaemic damage. Ectopic Pacemaker Activity: This is when another area of myocardium becomes spontaneously active and its depolarisations dominate over the SAN. ![]() a heartbeat with an irregular rate and/or rhythm. Increasing sympathetic outflow allows for further increases in heart rate.ĭisturbance to the natural pacemaker activity of the heart can lead to arrhythmias i.e. Initial increases in heart rate are brought about by a reduction in the parasympathetic outflow. The normal resting rate of about 60bpm is produced because the parasympathetic system dominates at rest. If all autonomic inputs are blocked, the intrinsic heart rate is about 100 beats per minute (bpm). This shortens the interval between impulses by making the pacemaker potential steeper, hence increasing the heart rate.
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