NR 340 Exam 2 Study Guide-Critical Care

NR 340 Exam 2 Study Guide-Critical Care Exam 2 Study Guide-Critical Care Basic Dysrhythmia Interpretation & Mgmt-Ch 7 Blood Flow Review Basic Electrophysiology • Automaticity-The ability for the heart muscle to generate it's own electrical activity o Pacemaker Cells arise naturally from the SA Node o Electrolytes involved are K+, Na+, & Ca+ Cardiac Action Potentials • Depolarization-occurs when charge is more (+) o P wave=atrial depolarization o QRS complex=ventricular depolarization o contraction o Systole • Repolarization-recharging period when charge is more (-) o T wave=ventricular repolarization o filling o Diastole • Electrical + Mechanical=Cardiac Contraction • Action Potential Curve o See Below-Sodium, Potassium, & Calcium flow in & out of the cell at different times allowing for charge changes and contraction of heart muscle tissue. o 4 Phases ▪ Early Repolarization • sodium channels close ▪ Phase 2-Plateau Phase • potassium leaves cell ▪ Phase 3-Rapid Repolarization • calcium channels close • potassium returns into cell quickly ▪ Phase 4-Resting Phase (polarized state) • active transport through the Na-K pump begins restoring K to inside the cell & sodium to the outside of the cell • cell membranes become impermeable to sodium • Potassium may move in & out of the cell Intrinsic Rates of Conduction Pathway • SA Node o natural pacemaker o 60-100 bpm • AV Node o takes over as pacemaker if SA node can't do the job o 40-60 bpm • Purkinje Fibers o last resort to pace heart if both SA & AV nodes fail o 20-40 bpm Cardiac Monitoring • 12 lead ECG o only 10 electrodes used to monitor, but gives 12 overall electrical pictures ▪ 4 limb leads ▪ 6 trunk leads o shows change or damage to heart muscle ▪ ischemia, infarct, enlarged cardiac chambers, electrolyte imbalances or drug toxicity Calculating Heart Rate from a 6 Second Strip • Graph Paper o Vertical boxes measure voltage or amplitude o Horizontal boxes measure time (in seconds) ▪ 1 small box=0.04 seconds ▪ 1 large box=0.20 seconds ▪ 5 large boxes=1 second • a six-second strip will be 30 large boxes • To calculate rate on a 6 second strip, count R-to-R and multiply by 10 Cardiac Waveforms & Determining Rhythm • P Wave • atrial depolarization • 0.04-0.10 seconds in duration ▪ Are they present? ▪ are they regularly occurring? ▪ is there a P for each QRS? ▪ are the P waves smooth, rounded, & upright? ▪ do all P waves look similar? • QRS Complex • ventricular depolarization • 0.06-0.10 seconds in duration ▪ is the complex 0.12 seconds (wide)? • can indicate ventricular origin ▪ is the complex 0.12 seconds (narrow)? • most likely supraventricular in origin (SA/AV nodes) ▪ do the complexes have a similar appearance across the tracing? • QT Interval • 0.38-0.42 seconds • begins at the QRS Complex to the end of the T wave • varies with heart rate • Pathological Q waves • 0.04 seconds in width & more than 1/4 R wave amplitude • indication of MI or myocardial tissue death • ST Segment • Elevation ▪ myocardial injury or hyperkalemia • STEMI ▪ looks like a tombstone • Depression ▪ myocardial ischemia or digoxin use • T Wave • ventricular repolarization • follows QRS Complex • U Wave • can sometimes bee seen after the T wave • can be normal or indicate hypokalemia • PR Interval • 0.12-0.20 seconds in duration ▪ is the interval 0.20 seconds? ▪ is the interval 0.12 seconds? ▪ is the interval constant across the tracing? Cardiac Dysrhythmias • Normal Sinus • Rate 60-100 • Rhythm regular • P waves before QRS & upright • PR interval 0.12-0.20 seconds • QRS complexes 0.12 seconds & look alike • Sinus tachycardia • Causes ▪ stress, exercise, fever, anemia, hypoxemia, CHF, pain • Effects on body ▪ faster rate decreases CO • S&S ▪ pounding heart, dizziness, anxiety, weak pulses ▪ decreased BP, UO • Treatment ▪ treat underlying cause ▪ give O2 ▪ if CHF, give Digoxin • Rate 100-160 • Rhythm regular • P waves before QRS & upright • PR interval 0.12-0.20 seconds • QRS complexes 0.12 seconds & look alike