May 13th Lecture #2 Part 2

Properties of Cardiac Muscle

  • Automaticity: Cardiac cells can generate electrical impulses independently.

  • Conductivity: Cardiac cells can transmit electrical impulses to other cardiac cells.

  • Excitability: Cardiac cells can respond to electrical stimuli by contracting.

Mechanical Events of Cardiac Cycle

  • The cardiac cycle involves both electrical impulses and mechanical events (systole and diastole).

  • Systole: Contraction phase, producing the "lub" sound.

  • Diastole: Relaxation phase, producing the "dub" sound.

  • Pulseless Electrical Activity (PEA): Electrical activity occurs without corresponding mechanical events (contraction).

Regulation of Cardiac Activity

  • Parasympathetic Nervous System:

    • Regulates heart rate via vagus nerve stimulation, slowing it down.

    • Slows SA node discharge, leading to bradycardia (slow heart rate).

    • Slows AV node conduction, increasing refractoriness, potentially causing heart block.

  • Sympathetic Nervous System:

    • Increases heart rate (fight or flight response), potentially causing sinus tachycardia (fast heart rate).

  • Alpha and Beta Receptors:

    • Alpha receptors: Found in smooth muscle; stimulation causes vasoconstriction (narrowing of blood vessels).

    • Beta receptors:

    • Beta-1: Found in the myocardium (heart muscle); stimulation increases heart rate and contractility.

    • Beta-2: Found in lungs and peripheral vessels; stimulation leads to vasodilation (widening of blood vessels) and bronchodilation (opening of airways).

Depolarization and Repolarization

  • Depolarization (Contraction):

    • Potassium (K+K^+) moves from inside to outside of cells.

    • Sodium (Na+Na^+) moves inside cells.

  • Repolarization (Relaxation):

    • Potassium (K+K^+) moves back inside cells.

    • Sodium (Na+Na^+) moves back outside cells.

Coronary Perfusion

  • Oxygenation of heart muscle occurs via blood from the right and left coronary arteries.

  • Coronary arteries originate from the aorta at the coronary openings.

  • They deliver oxygen and nutrients to different parts of the heart, ensuring proper function.

Arteries Supplying the Heart

  • Left Anterior Descending Artery (LAD):

    • Supplies blood to the left surface and anterior part of the left ventricle.

    • Supplies the anterior surface of the ventricular septum.

  • Circumflex Artery:

    • Wraps around the heart, supplying the left atrium.

    • Supplies the lateral aspect and posterior surface of the left ventricle.

  • Right Coronary Artery (RCA):

    • Supplies the right side of the heart, including the right atrium and ventricle.

Normal Electrical Conduction

  • SA node (60-100 bpm) → AV node (40-60 bpm) → Purkinje fibers (20-40 bpm).

  • Depolarization (contraction) and repolarization (relaxation) are needed for a pulse.

  • Without both, pulseless electrical activity (PEA) occurs.

Components of Normal Electrical Conduction

  • SA Node: Located below the superior vena cava, above the right atrium; the heart's primary pacemaker.

  • AV Node: Backup pacemaker if the SA node fails.

  • Purkinje Fibers: Assume pacemaker role if both SA and AV nodes fail.

  • Bundle Branches:

    • Bundle of His divides into right and left bundle branches.

    • Purkinje fibers then spread the electrical signal.

EKG Leads

  • Lead I: Measures the electrical potential between the right arm (negative) and left arm (positive).

  • Lead II: Measures the electrical potential between the right arm (negative) and left leg (positive).

  • Lead III: Measures the electrical potential between the left arm (negative) and left leg (positive).

12-Lead EKG

  • Uses 10 electrodes to view 12 different sections of the heart, providing a comprehensive assessment.

EKG Electrode Placement

  • Five-lead placement (telemetry): White, green, black, red, brown.

  • If hair is present, trim or clip; do not shave to avoid micro-cuts and infection.

  • Clean site with alcohol to ensure good adhesion.

  • Replace electrodes daily and mark with the date to ensure timely changes for good readings and prevent artifacts.

Preparing Patient for 12-Lead EKG

  • Clip chest hair with patient's permission to improve lead adhesion.

  • Respect patient privacy and obtain consent before clipping hair.

  • If patient is unresponsive and no family is available, proceed with doctor's order and document.

Components of EKG Graph

  • P wave, PR interval, QRS complex, ST segment, T wave.

  • U wave: Usually after the T wave and smaller; indicates hypokalemia (low potassium).

EKG Complex

  • P wave: Atrial depolarization (atrial contraction).

  • PR segment: Shows delay at AV node, allowing atria to contract fully before ventricles.

  • QRS complex: Ventricular depolarization (ventricular contraction).

  • Isoelectric line: No electrical activity, serving as a baseline.

  • Atrial repolarization: Hidden by ventricular depolarization.

EKG Time and Voltage

  • One big box:

    • Voltage: 5 mm.

    • Time: 0.2 seconds.

  • One small box:

    • Voltage: 1 mm.

    • Time: 0.04 seconds (important for measuring PR interval, QRS complex, QT interval).

Isoelectric Line

  • Neutral line; anything above is positive, anything below is negative, helping to identify deviations.

EKG Intervals and Segments

  • PR interval: Beginning of P wave to beginning of QRS complex, indicating AV conduction time.

  • QRS complex: Q to J point, representing ventricular depolarization.

  • ST segment: Beginning of ventricular repolarization, sensitive to ischemia.

  • QT interval: Entire ventricular activity (depolarization and repolarization).

ST Elevation

  • ST segment is more than 1 mm above the isoelectric line; indicates myocardial injury (not always MI; can occur in heart failure).

ST Depression

  • ST segment is more than 1 mm below the isoelectric line; signifies old infarct or ischemia.

Steps in Rhythm Recognition

  1. Rhythmicity: Regular or irregular.

  2. Rate: Atrial and ventricular (focus on ventricular).

  3. P wave: Present or absent, rounded or peaked.

  4. PR interval: Short, absent, or prolonged.

  5. QRS complex: Wide, narrow, or normal.

Rhythm Regularity

  • Measure distance between R-R waves using a six-second strip.

  • Six-second strip: 30 big boxes.

  • Use calipers to measure R-R intervals without rotating to avoid errors.

Heart Rate Measurement

  • Irregular Rhythm: Count the number of R waves in a six-second strip and multiply by 10.

  • Regular Rhythm: Count the number of small boxes between one R to the next R, then divide 1,500 by that number.

    • HeartRate=1500Number of Small BoxesHeart Rate = \frac{1500}{\text{Number of Small Boxes}}

    • 1,500 comes from 60 seconds / 0.04 (time for a small box).

P Wave Analysis

  • Check if P waves are present and if there's one before every QRS complex.

  • Assess if P waves are rounded and look the same.

  • Different shapes of P waves are okay if there are just two shapes.

  • If there are more than two different shapes of P waves, it's called a Wandering Atrial Pacemaker (WAP).

Wandering Atrial Pacemaker (WAP)

  • More than two different shapes of P waves indicate that the heart's pacemaker is wandering.

  • Inverted P waves originate from the AV node; upright P waves originate from the SA node.

PR Interval Measurement

  • Normal PR interval: 0.12 to 0.20 seconds.

  • Measure from the beginning of the P wave to the beginning of the QRS complex.

  • Multiply the number of small boxes by 0.04 seconds to get the PR interval.

  • A short PR interval with an inverted P wave indicates junctional rhythm.

Prolonged PR Interval

  • A consistently prolonged PR interval indicates a first-degree heart block.

QRS Complex Analysis

  • Normal QRS complex: 0.06 to 0.12 seconds.

  • Measure from the beginning of the Q wave to the S wave or J point.

  • A QRS complex is considered narrow if it's below 0.12 seconds.

  • A QRS complex is considered wide if it's more than 0.12 seconds, indicating a bundle branch block (BBB).

Interpretation of Rhythm

  • Normal Sinus Rhythm (NSR): Regular rhythm, heart rate of 60-100 bpm, P waves present and the same, PR interval of 0.12-0.20 seconds, QRS complex normal.

  • Sinus Rhythm with First-Degree AV Block: Sinus rhythm with prolonged PR interval.

Analyzing Strips

  • Sinus Bradycardia: All components of NSR except heart rate is less than 60 bpm.

  • Sinus Tachycardia: All components of NSR except heart rate is 101-150 bpm.

  • Supraventricular Tachycardia (SVT): Heart rate of 151-250 bpm, faster than sinus tachycardia.

  • Sinus Arrhythmia: Components of sinus rhythm except the rhythm is irregular.

Dysrhythmias

  • Disturbances in rate, rhythm, or both.

  • Atrial dysrhythmias: PAC, atrial flutter, atrial fibrillation.

  • Ventricular dysrhythmias: PVC, V-tach, V-fib, idioventricular rhythm, asystole.

Atrial Dysrhythmias

  • Premature Atrial Contraction (PAC): Problem with the P wave, where it arrives prematurely.

  • Atrial Flutter: Rapid atrial activity with saw-tooth pattern.

  • Atrial Fibrillation (AFib):

    • Controlled AFib: Ventricular rate is 100 bpm or less.

    • Uncontrolled AFib (AFib with rapid ventricular rate (RVR)): Ventricular heart rate is more than 100 bpm.

Ventricular Dysrhythmias

  • Premature Ventricular Contraction (PVC): Bizarre QRS complex.

  • Ventricular Tachycardia (V-tach): Rapid ventricular activity.

    • Monomorphic V-tach: One shape.

    • Polymorphic V-tach: Different shapes.

  • Ventricular Fibrillation (V-fib): Coarse or fine, indicating chaotic electrical activity.

  • Asystole: Straight line, indicating no electrical activity.

    • P wave asystole: P waves present, but no mechanical activity.

Conduction Abnormalities

  • Heart Blocks:

    • First-degree AV block: Prolonged PR interval.

    • Second-degree AV block:

    • Type 1 (Mobitz I or Wenckebach): Progressively prolonged PR duration until non-conducted P wave.

    • Type 2 (Mobitz II): Some P waves are not followed by a QRS complex.

    • Third-degree AV block (complete heart block): Atria and ventricles beat independently.

Assessment with Dysrhythmias

  • Health history, medications, psychosocial assessment to understand underlying causes and impacts.

  • Physical assessment: Skin, heart sounds, heart rate, rhythm, blood pressure to evaluate the patient's condition.

Potential Complications of Dysrhythmias

  • Cardiac arrest: Sudden cessation of heart function.

  • Heart failure: Inability of the heart to pump enough blood.

  • Thrombotic events (especially with AFib): Formation of blood clots due to irregular heart activity.

    • 90% of embolic strokes are cardiac in origin, commonly AFib.

Interventions

  • Monitor vitals, signs of inadequate cardiac output to detect deterioration.

  • Administer antiarrhythmic medications (metoprolol, amiodarone, cardizem, digoxin) to control rhythm.

  • Minimize anxiety with anti-anxiety medications; promote a sense of community.

Nursing Assessment Question

  • A patient displays progressively prolonged PR duration until there is a nonconducted P wave, expect Second-degree AV block Type 1 (Wenckebach).

Adjunctive Modalities and Management

  • Used when medications alone are ineffective.

  • Pacemaker: Electronic device that provides electrical stimuli to the heart.

    • Used to initiate heartbeat when SA node is damaged or conduction is impaired.

    • Types: Transcutaneous, transvenous, implantable (permanent).

  • Cardioversion: Synchronized electrical shock to restore normal rhythm.

  • Defibrillation: Unsynchronized electrical shock to stop life-threatening arrhythmias.

Pacemakers

  • Used for symptomatic bradycardia to increase heart rate.

  • Atropine is given for symptomatic bradycardia as a temporary measure.

    • Dose: 1 mg every 3-5 minutes, max of 3 mg.

Pacemaker Types

  • Transcutaneous: Temporary, pads used like a defibrillator.

  • Transvenous: Temporary, inserted through a vein.

  • Implantable: Permanent, surgically implanted.

  • Caution Patients with New Pacemakers: do not overuse the arm on the side of pacemaker placement to avoid dislodging the wire.

Possible Indications for Pacemaker

  • Sick Sinus Syndrome (SSS) (SA Node Failure).

  • Second-degree Type II AV block.

Normal QT Interval

  • 0.36 to 0.44 seconds, varies with heart rate.

Pacemaker Components

  • Generator: Contains the battery and circuitry.

  • Leads: Single or dual chamber, delivering the electrical impulse to the heart.

  • Modern pacemakers can also function as Implantable Cardioverter Defibrillators (ICDs).

Pacemaker Codes

  • A-pace: Atrial pacing.

  • V-pace: Ventricular pacing.

  • AV-pace: Dual pacing (atrial and ventricular).

Pacemaker Malfunctions

  • Failure to pace: Pacemaker doesn't fire, no electrical impulse is generated.

  • Failure to capture: Pacemaker fires, but no depolarization occurs, the heart doesn't respond.

  • Under sensing (failure to sense): Pacemaker fires even though the heart is beating on its own, leading to unnecessary pacing.

  • Troubleshooting: Check cable, battery, interrogate pacemaker to diagnose the issue.

Complications of Pacemaker Use

  • Dislodgement of wire or lead, requiring repositioning.

  • Avoid overusing arm on the pacemaker side to prevent dislodgement.

  • Infection, bleeding, hematoma at the insertion site.

Cardioversion and Defibrillation

  • Cardioversion: Lower joules, synchronized to the R wave to avoid inducing VF.

  • Defibrillation: Higher joules, not synchronized, used in emergencies.

  • Remember to yell clear, and stop the oxygen to ensure safety.

Implantable Cardioverter Defibrillator (ICD)

  • Used for patients at risk for lethal dysrhythmias.

  • Senses and defibrillates, delivering a shock when a dangerous rhythm is detected.

Life Vest

  • Worn by patients with EF less than