Exam 2 Study Guide-Critical Care updated 2020

Exam 2 Study Guide-Critical Care updated 2020

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

•             Sinus bradycardia

•             Causes

 athletes, acute spinal cord injury

•             Effects on body

 lower rate decreases CO

•             S&S

 dizziness, SOB, weak pulses

•             Treatment

 Atropine by IV bolus to increase heart rate

•             0.5 mg q3-5 minutes for a total dose of no more than 3 mg

•             S/Es: dry mouth/eyes, blurry vision, decreased UO, further slowing of heart rate if <0.5 mg are given

•             Rate < 60

•             Rhythm regular

•             P waves before QRS & upright

•             PR interval 0.12-0.20 seconds

•             QRS complexes <0.12 seconds & look alike

Atrial Rhythms

•             Causes

o Stress response, electrolyte imbalances, hypoxia, atrial injury, Dig toxicity, hypothermia o hyperthyroidism, alcohol, pericarditis, drugs

•             Premature Atrial Contractions (PACs)

•             early beats initiated by the atria not the SA node resulting in an early P wave

•             P waves & PR intervals may vary and are not at a regular rhythm

•             normal QRS Complexes

•             Precursor to other atrial tachycardias

•             S&S

             palpitations, heart skipping or pausing

•             Supraventricular tachycardia (SVT)

•             Causes

             heart disease, use of digoxin

•             Effects on body

             rhythm can come & go

             decreases CO

•             S&S



•             Treatment

             O2, start an IV, vagal maneuvers/valsalva, carotid massage

             adenosine by rapid IV push to block AV node transmission & stop heart briefly

•             6 mg rapid IV push initially, followed by a second bolus of 12 mg 2 minutes later if not convert back to NSR o all doses followed by flush of NS and raising of arm

•             monitor HR, BP, and rhythm pattern

•             Have crash cart and/or defibrillator present in room

•             S/Es: diaphoresis, facial flushing, lightheadedness, chest pain

             Beta Blockers (Metroprolol, Labetalol)

•             decreases HR & BP, cardioprotective effects for MI patients

•             slow IV push

•             continuous monitoring of BP, HR, & rhythm o do NOT give for HR less than 50 or with 2nd or 3rd* heart block

•             S/Es: bradycardia, hypotension, heart failure

             Calcium Channel Blocker (Diltiazem, Verapamil)

•             slows conduction through AV node & decreases HR

•             Diltiazem 15-20 mg slow IV push over at least 2 minutes with a repeat bolus of

20-25mg if needed can be given after 15 minutes o IV infusion rate of 5-15 mg/hr may be started & titrated to desired HR

•             Verapamil 2.5-5 mg slow IV push over at least 2 minutes; if no response, can give repeat boluses of 5-10 mg every 15-30 minutes for a total dosage of 20 mg

•             S/Es: hypotension, bradycardia, flushing, burning at injection site, CHF, heart block

•             Rate 150-250

•             Rhythm regular

•             P waves usually not discernible, especially at high rates

•             PR interval usually not discernible

•             QRS complexes <0.12 seconds & look alike

•             Atrial fibrillation-

•             Causes:

             CHF, ischemic or rheumatic heart disease, pulmonary disease

•             Effects on Body

             decreases CO

•             S&S

             palpitations

•             Treatment