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Automaticity

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Cardiac muscle can generate its own electrical activity

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Cardiac cycle

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Two activities: 1. Electrical (caused by automaticity) 1a. Depolarization = active --> stimulates contraction 1b. Repolarization = resting 2. Mechanical (muscular) = contraction 2a. Systole-contraction 2b. Diastole-relaxation

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Depolarization process

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Leads to systole/contraction • Na+ outside, K+ inside • Change cell permeability • Na+ enters, K+ exists • Ca2+ slowly enters cells • ATP needed to move electrolytes back to resting state

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Cardiac Conduction Pathway

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Begins in SA node (60-100 bpm) → Atrial contraction → AV node (60-80 bpm) → Bundle of His → L and R Bundle branches → Ventricles (Purkinje fibers) (15-40 bpm)

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Interpreting the EKG steps

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1. Determine the heart rhythm 2. Measure the heart rate 3. Examine the P waves 4. Examine the P to QRS ratio 5. Measure the PR interval 6. Examine the QRS complex 7. Interpret the rhythm

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P wave

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• Represents electrical firing from SA node • Atrial depolarization • Not to exceed 3 boxes high

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PR segment/interval

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• Atrial depolarization/delay in AV node • Results from short pause in electrical conduction as the wave of depolarization slows down while traveling through AV junction • Normal: 0.12-0.20 second • 0.20 seconds = First-degree AV block

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QRS complex/interval

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• Ventricular depolarization 1. Q wave = First negative (downward) deflection after P wave 2. R wave = First positive (upward) deflection after P wave 3. S wave = Negative waveform after R wave • Not everyone has traditional QRS • Normal: 0.06-0.10 seconds (narrow complex) • Wider complex = Further away from SA node

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Pathologic Q waves

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• ≥ 1 box (0.04 seconds) in width • More than 1/4 of R wave amplitude Indication of myocardial infarction/tissue death and necrosis (In an acute MI, you won't see the Q wave until tissue has been necrotic)

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ST Segment

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• Look for depression or elevation • ST elevation = Myocardial injury • ST depression = Reciprocal changes, digoxin, and ischemia

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T wave

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• Ventircular repolarization • Follows QRS complex • Bigger than P wave, but no greater than 5 small boxes high • Peaked T wave = Hyperkalemia • Inverted T wave = Ischemia in myocardium

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QT Interval

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• Beginning of QRS complex to end of T wave • Normal: 0.32-0.50 seconds • >0.40-0.45 = Look at drugs that prolong QT interval causing escape rhythms/beats (i.e. amiodarone); longer when HR is slower

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U Wave

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• Sometimes after T wave • Unknown origin • May be normal or hypokalemia

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Normal Sinus Rhythm

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• Regular rhythm • Rate: 60-100 bpm • Normal P wave • P wave before each QRS • Normal PR, QRS, and QT

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Sinus Dysrhythmia

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• Sinus rhythm • Rate varies with respirations • Inspire = Increase • Expire = Decrease • Rarely affects hemodynamic status • Speeds up, slows down, speeds up, etc.

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Sinus Tachycardia

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• Sinus rhythm • Rate: 100-150 bpm • Causes: Stimulants, exercise, fever, alterations in fluid status • N/I: Assess for s/s of low cardiac output

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Sinus Bradycardia

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• Sinus rhythm • Rate: <60 • Causes: Vagal maneuvers (i.e. bearing down, icing), ischemia, elevated intracranial pressure (ICP), and athletes (normal) • Produces various hemodynamic responses

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Sinus Arrest or Exit Block

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• Sinus node fails to initiate impulse • Causes: Vagal responses, heart disease, drugs that slow HR • HR can be normal or slow • Irregular rhythm • Decrease cardiac output

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Atrial Dysrhythmias: Defintion + causes

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• Increased automaticity in the atrium • Generally have P-wave changes • Causes: -Stress -Electrolyte imbalances -Hypoxemia -Atrial injury -Digitalis toxicity -Hypothermia -Hyperthyroidism -Alcohol -Pericarditis

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Premature Atrial Contractions (PAC)

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• Early beats initiated by atrium • P waves and PR interval may vary • Non-compensatory pause • P wave may be found in T wave

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Blocked Premature Atrial Contractions

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• Pause noted on rhythm strip • Premature P wave • May alter cardiac output

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Wandering Atrial Pacemaker

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• SA node not fully in control; May give some beats but mostly ectopic (outside stimuli) • Varying configurations of P waves (since different areas of atrium) • At least 3 different looking P waves must be seen • HR < 100 • PR interval varies • Irregular rhythym

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Multifocal atrial tachycardia (MAT)

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• Similar to wandering atrial pacemaker but faster (>100 bpm)

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Paroxysmal atrial tachycardia (PAT, PSVT)

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• Without warning, sudden onset of very fast tachycardia • HR 150-250 bpm • Regular rhythm • P waves (if present) may merge in T waves • AV block • Ectopic foci in atria rapidly fluttering • QRS complex is normal • Hemodynamic effects vary • S/S: Sudden onset palpitations, racing heart • Tx: 1. Adenosine (blocks atrial beats for 6 seconds so SA can reset as primary pacemaker) 2. Beta blockers (slow down heart rate)

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Atrial flutter

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• Ectopic foci in atria, heart disease • Classic "sawtooth" pattern • Atrial rate fast and regular (250-350 bpm) with AV block • Degree of conduction varies; may be 3 P waves: 1 QRS complex

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Atrial fibrilation

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• Erratic impulse formation in atria • No discernible P wave • Irregular R-R intervals* • Aberrant (normal) ventricular conduction can occur • Results in loss of atrial kick = decreased cardiac output, pooling blood • High risk for pulmonary or systemic emboli • New onset patients feel weak, lightheaded • Maintain with anticoagulants

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Junctional (Nodal) Rhythms

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• Regular rhythm • PR interval low end of normal • P-wave changes - May be absent or retrograde (because stimulus from AV node) • Normal rate: 40-60 bpm • Decreased CO possible

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Junctional tachycardia

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• Rate 60-100 bpm for accelerated junctional rhythm • Rate 100-150 bpm for junctional tachycardia

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Premature junctional contractions (PJC)

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• P-wave changes • PR interval shorter than normal (because closer to ventricle) • Usually noncompensatory pause • QRS complex that is irregular with the rest of the waves and changing P waves

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Ventricular dysrhythmias + causes

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• Impulses initiated from lower portion of heart (i.e. Bundle of His) • Depolarization occurs, leading to abnormally wide QRS complex • Ectopic and escape beats • Common causes: 1. Myocardial ischemia, injury, and infarction 2. Low potassium or magnesium 3. Hypoxemia 4. Acid-base imbalances

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Premature ventricular contractions (PVCs)

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• Wide and bizarre beats • Compensatory pause • Patterns: -Bigeminy and trigeminy -Couplets and triplets • Uniforcal vs multifocal (depends on morphology) • QRS complex >0.10 second • Irregular rhythm (d/t early beats and compensatory pause) • Absent P waves • Assess and treat cause: 1. Hypoxia 2. Ischemia 3. Electrolyte imbalance • May need antiarrhythmic agents

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Ventricular tachycardia

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• Rapid, life threatening • Three or more PVCs in a row • Fast rate (>100 bpm) • Initiated by ventricles • Wide QRS, no P waves before each beat • Usually regular • May or may not have a pulse --> Treat pulseless same as v-fib • Significant loss of cardiac output • Hypotension • Tx: Cardioversion w/ external defibrilator or medications

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Ventricular fibrilation

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• Chaotic pattern • No discernible P, Q, R, S, or T waves • Coarse versus fine • No cardiac output; life threatening • Emergent defibrilation

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Idioventricular rhythm

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• Hallmark = Very slow • Escape from Purkinje fibers • Rate: 15-40 bpm • Regular rhythm • Wide QRS interval • No P waves

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Accelerated idioventricular rhythm

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• Same as idioventricular rhythm • Rate > 40 bpm • Hemodynamic effects correspond to heart rate

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Ventricular standstill (asystole)

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• No P, Q, R, S, T waveforms • Assess in two leads (EKG may be off) • No cardiac output • Death

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Pulseless electrical activity (PEA)

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• EKG rhythm but no pulse • Causes: H's & T's

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H's & T's

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H: 1. Hypoxia 2. Hypovolemia 3. Hypothermia 4. H+ ions (acidosis) 5. Hypokalemia or hyperkalemia T: 1. Tablets (overdose) • Tamponade (cardiac) • Tension pneumothorax • Thrombosis (coronary) • Thrombosis (pulmonary)

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Atrioventricular blocks (AVB)

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• Block of conduction from atria to ventricles • Causes: 1. Coronary artery disease 2. Myocardial infarction (eg inferior wall) 3. Infections 4. Enhanced vagal tone 5. Drug effects (eg digoxin toxicity)

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Normal EKG intervals

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• PR interval = 0.12-0.20 seconds • QRS <0.12 seconds (0.06-0.10 seconds) • QT interval = 0.32-0.50 seconds

Dysrhythmia Interpretation and Management/EKG – Flashcards

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