Cardiac dysrhythmia (arrhythmia):Irregular heart action caused by physiological or pathological disturbances in the discharge and transmission of impulses through the conductive tissue of the heart•Depolarization:reversal of the electrochemical charges at the cell membrane in an excitable cell; this produces and electrical charge that will cause cardiac muscles to contract•Repolarization: return of the electrochemical charges at the cell membrane to theresting polarized state•Absolute refractory period:no transmission of electrochemical impulse is possible•Relative refractory period: abnormal transmission of electrochemical impulse occur; stressors/disease extend refractory periods•Electromechanical dissociation: electrochemical impulse does not produce muscle contraction; seen in severe cardiomyopathy•Asystole: absence of electrical activity and contraction of the heart•Conductivity:the ability of the heart muscle to transmit of electrochemical impulse from one cell to another; some cells are more efficient conductors than others (increased conductivity)•Automaticity: the unique ability of the heart muscle to initiate an electrochemicalimpulse without nervous stimulation•Pacemaker: specialized groups of cells that can initiate impulses; most cardiac cells can become pacemaker•Contractility: ability of muscle cells to contract
•Automatic pacemaker rates (potential ectopic sites)Atrial = 75AV node = 40-60Ventricles = 15=40SA node fires normally 60-100 bpm•Tachycardia: rapid beat (above 100 bpm)•Bradycardia: slow beat (below 60 bpm)•Sinus dysrhythmia: defect starts in SA node•Atrial dysrhythmia: defect in starts in atria•Nodal/Junctional dysrhythmia: defect starts in AV Node•Ventricular dysrhythmia: defect in starts ventriclesFibrillation:rapid irregular electrical activity which results in quivering cardiac muscle and ineffective ejection of blood form the chamberBlock: failure of conduction of impulseFirst degree heart block:slow impulse from atria to ventriclesSecond degree heart block: not every impulse gets transmitted from atria to ventriclesThird degree (complete) heart block:atria and ventricles no longer communicate; each beats independentlyBundle branch block: slow or incomplete conduction through the Bundle of His in the ventriclesPremature beats (come early and are followed by compensatory pause)PAC (PAB) premature atrial contractions
PVC (PVB) premature ventricular contractionsPAC’s have no P wave but QRS looks normalPVC’s have no P wave but QRS is wide and abnormalEpidemiology:•Very common problem but seen more in older adult•10% of people over 70 have A. Fib•Some very well tolerated and undiagnosed•Some life threatening•Over 1 million in USA have pacemakerRisk Factors:•Damaged cardiac tissue•Hypoxia•Electrolyte disturbances (especially K+)•Stimulants such as caffeine & cocaine•Endocrine: hyperthyroidism, adrenaline•Fever, anxiety, pain•
