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In ventricular cells, RMP keeps on resting until the nearby cells throw some cations into the cells and these cells will undergo depolarization and it has a long plateau phase due to k+ efflux and entering of Ca++ at the same time. In this way, normal automaticity is enhanced after the action of epinephrine on the SA Node. When you stimulate SA Node with epinephrine or norepinephrine, stimulating the Beta-adrenergic receptors, eventually leading to phosphorylation of some additional Ca++ channels and additional Ca++ comes in, this added ca++ helps the cells to move RMP towards threshold potential more rapidly and there is frequent production of the action potential. In SA Node, cell have leaky Na+ channels, when Na+ enters into cell, the RMP cannot really rest because incoming Na+ will take RMP towards the threshold when RMP reaches up to the threshold, there is an opening of voltage-gated Ca++ channels, this produces Ca- dependent depolarization and then the opening of voltage-dependent K-channels and K+ efflux occurs and the membrane becomes again repolarized. SA Node works as a pacemaker because it has a tendency to undergo depolarization spontaneously. It is defined as: вЂњProperty of any excitable tissue which can undergo depolarization spontaneously.вЂќ How automaticity is increased? The following are the mechanisms of Cardiac Arrhythmias: Sinus arrhythmias, atrial arrhythmias, and junctional arrhythmias are also called supraventricular arrhythmias because these arrhythmias are generated above the ventricles. If there are abnormal rhythms or Cardiac Arrhythmias originating due to abnormalities with the ventricles we call them When there are, abnormal rhythms or Cardiac Arrhythmias related to AV Node or related to the junction between the atrium and ventricle called junctional arrhythmias. Junctional arrhythmias (Nodal Arrhythmia) These abnormal rhythms or Cardiac Arrhythmias which are due to abnormal activity within the atrial myocardial tissue are called atrial arrhythmias.ДЈ.

On the basis of the main site where abnormal rhythm is generated, we can classify arrhythmias as:ДЄny abnormal rhythms or Cardiac Arrhythmias which come from SA Node called Sinus arrhythmia. When the heart rate is between 20 вЂ“ 40 bpm c. When the heart rate is between 40 вЂ“ 60 bpm If the heart rate is less than 60 bpm we call such type of Cardiac Arrhythmias as Bradyarrhythmias, which are further classified as: When the heart rate is more than > 350 bpm When the heart rate is between 250 вЂ“ 350 bpmД.Fibrillation (Atrial or Ventricular Fibrillation): When the heart rate is between 150 вЂ“ 250 bpmД¬. When the heart rate is between 100 вЂ“ 150 bpmД«. When the heart rate is more than 100 bpm we call such type of Cardiac Arrhythmias as Tachyarrhythmias, which are further classified as: On the basis of heart rate arrhythmia can be classified as Normal cardiac rhythm has the following criteria:Д®very heartbeat should be originated from the SA Node.ДЄll cardiac impulses should be passed through a normal conduction pathwayД¬ardiac impulse should be passed through a normal pathway with normal velocity When the heart deviates from the normal rhythm is called arrhythmia so irregular rhythms of heartbeats are known as Cardiac Arrhythmias. Master Medical Sciences with crystal clear concepts.

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