Dysrhythmias

Automacticity

Ability to initiate an impulse spontaneously and continuously

cardiac arrest and acid-base imbalance

Acid-base imbalance is not unexpected after cardiac arrest. With cardiac arrest, there is poor tissue perfusion and hypoxemia which can result in a lactic acidosis, a form of metabolic acidosis. These arterial blood gas values reflect acidosis (low pH), of metabolic origin (low bicarbonate, HCO3) -- metabolic acidosis. PaCO2 (carbon dioxide) is normal. Alkali (NAHCO3 therapy, sodium bicarbonate) may be administered if acidosis is severe with cardiac arrest (pH less than 7.15), to improve heart function and lactate utilization. With return of cardiac function after cardiac arrest and administration of oxygen, the cause of acidosis (hypoxemia) should be corrected.

Unsyncronized Cardioversion

Defibrillation It involves the passage of electrical shock through the heart to depolarize the myocardial cells High energy shock for ventricular fibrillation and ventricular tachycardia. According to ACLS guidelines, after two unsuccessful defibrillation attempts, treatment with a vasopressor should be initiated. Guidelines call for epinephrine IV push. Epinephrine 1 mg can be administered every 3-5 minutes. According to ACLS guidelines, vasopressin 40 units IV push can be administered to replace either the first or second dose of epinephrine. A 20-ml bolus of IV fluid should be infused after an IV bolus drug, to expedite flow of the drug into the systemic circulation. Cardiopulmonary resuscitation (CPR) should be continued as drugs are administered. CPR should not be interrupted for administration of drugs. Since an advanced airway in place, CPR should include chest compressions that are continuous, and ventilations that are delivered at a rate of 8-10 per minute. Note: NEVER place over pacemaker

Phases of cardiac action potential

Each phase represents a specific electrical event or combination of electrical events The action potential has 5 phases Phase 0 is the upstroke of rapid depolarization and corresponds with ventricular contraction Phase 1, 2, and 3 represent repolarization Phase 4 is known as complete repolarization (or the polarized state) and corresponds to diastole RP = resting membrane potential TP = threshold membrane potential

Pacemaker

Electronic device that is used to pace the heart when the normal conduction pathway is damaged consists of a programmable circuitry, pacing leads, power source, and the myocardium

Conduction system of the heart

Generates and delivers (conducts) the electricity to all the muscle fibers of the heart resulting in a smooth, complete contraction of the cardiac muscle fibers, which forcefully ejects the blood outside the heart. SA node, AV node, bundle of His, bundle branches, and Purkinje fibers

Synchronized Cardioversion

Is the electrical management of choice for atrial fibrillation, atrial flutter, supra ventricular tachycardia (SVT), bradycardia, heart blocks

implantable cardioverter defibrillator (ICD)

Sensing system that monitors HR and rhythm - delivers 25 joules or less to heart when it detects lethal dysrhythmia Important for patients who survived SCD, have spontaneous sustained VT, have syncope with inducible VT or VF during EPS, or are at high risk for future life-threatening dysrhythmias (cardiomyopathy) Complications: Malfunctions can deliver unnecessary shocks. Consider applying magnet to device to permanently disable the device

Cardiac Action Potential: Ions

The membrane of the the heart is semipermeable which allows it to maintain a high concentration of potassium and a low concentration of sodium inside the cell and a high concentration of sodium and low concentration of potassium outside the cell. The inside of the cell, when at rest or in the polarized state, is negative compared with the outside. When cells are stimulated, the cell membrane changes its permeability. This allows sodium to move rapidly into the cell, making the inside of the cell positive compared to the outside (depolarization). A slower movement of ions across the membrane restores the cell to the polarized state (repolarization)

Which action by the nurse is most important when preparing for cardioversion of a client with atrial fibrillation? Charge defibrillator to the maximum energy level. Assure that the cardiac monitor alarm is turned on. Set synchronizer switch on defibrillator to the 'on' position. Take client's apical pulse for a full minute before the procedure.

Turning the synchronizer switch on ensures that the shock will not be delivered on the client's T wave, which could cause ventricular fibrillation. The defibrillator energy level is typically set to a low level for cardioversion, although higher levels may be used if the initial cardioversion attempt is unsuccessful. The cardiac monitor alarm may be off during cardioversion because the shock is likely to set off the alarm and the cardiac rhythm and rate are being monitored during the procedure. An apical pulse for a full minute is appropriate for a client with atrial fibrillation but is not needed when the client is on a cardiac monitor.

Excitability

ability to be electrically stimulated

Contractility

ability to respond mechanically to an impulse

Conductivity

ability to transmit an impulse along a membrane in an orderly manner