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Ecg workshop part one
 

Ecg workshop part one

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    Ecg workshop part one Ecg workshop part one Presentation Transcript

    • ECG Workshop: PART ONE Kathleen Brownrigg, BSc, RN, MScN July 2011
    • Cardiac cycle = Cardiac outputFilling + Contraction = Cardiac Cycle •Systole •Diastole Lub Dub
    • Cardiac Cycle
    • Mechanical Activity of the Heart Diastole Systole Semilunar valves open Atrioventricular Valves closed
    • Cardiac output CO = HR X SVThe amount of blood ejected Affected by: The amount of bloodfrom the heart per minute. -Physical factors ejected from theNormal (adults)= 4-6L/min -Nervous system heart with eachNormal (children) = -Environment contraction. -Electrolytes Affected by: …ect… PRELOAD AFTERLOAD CONTRACTILITY
    • Preload• Frank Starling’s Law of  Degree of fiber stretch as a result of a quantity of blood placed on the Heart the muscle prior to contraction.  The more diastolic volume or fibre stretch at end diastole, the greater the force of the next contraction during systole  Measured by LVEDP - left ventricular end diastolic pressure - prior to systole (max. full)  Normal value 6-12 mmHgAbility of the muscle fibers to stretch  The > stretch = > contractilityaccording to incoming volume.  If preload increases so does C.O.
    • AfterloadThe resistance to which the ventricles must overcome to eject blood.Resistance to blood flow as it leaves the ventriclesSVR on the Lt sidePVR on the RT side As resistance , stroke volume 
    • ContractilityThe ability of the myofibrils to shorten in length and produce a contraction.Not measured directlyFactors that affect contractility: PRELOAD AFTERLOAD DRUGS CARDIAC OXYGENATION FUNCTIONAL MYOCARDIUM
    • Electrical Activity of the Heart
    • The HeartELECTRICAL PROPERTIES MECHANICAL PROPERTIES AUTOMATICITY CONTRACTILITY CONDUCTIVITY CARDIAC OUTPUT BP Perfusion (capillary refill) EXCITABILITY LOC Pulses ECG
    • Conduction System of the Heart
    • Intra- and extracellular ion concentrations (mmol/L) Element Ion Extracellular Intracellular Ratio Sodium Na+ 135 - 145 10 14:1 Potassium K+ 3.5 - 5.0 155 1:30 Chloride Cl- 95 - 110 10 - 20 4:1 Calcium Ca2+ 2 10-4 2 x 104:1Although intracellular Ca2+ content is about 2 mM, most of this is bound or sequestered in intracellular organelles (mitochondria and sarcoplasmic reticulum).
    • MyocardialContractile Action Potential
    • Myocardial Contractile Cell: Action Potential• Phase 0: Depolarization phase, Na+ channels open and rapid influx of Na+ into cells• Phase 1: Repolarization phase (brief) cause by inactivating Na+ influx and activation of outward K + current.• Phase 2: Plateau phase cause by slow inward Ca++ current and decreased K+ efflux.• Phase 3: Rapid repolarization to resting potential due to outward K+ current• Phase 4: Resting membrane potential, Na+ moves out of cell and K+ moves into cell via an active pump (Na+/K+ pump)
    • Summary of Electrical Pathway• Distinct ion channels drive the depolarization and repolarization of cardiac cells during action potential.• Na+ channels (dominant in cardiac cells) depolarize quickly, but Ca++ channels (dominant in the SA and AV nodes) depolarize slowly.• The cell cannot respond to stimuli during the refractory period, except late in phase 3 when it can respond to strong stimuli.• The cell can respond again when it is completely repolarized.
    • Linking Conduction to the Cardiac CyclePressure (mmHg)Aortic blood flow(L/min) Ventricular volume (mL) Heart soundsVenous pulse Electrocardiogram
    • ECG Cycle
    • The Principals of Cardiac Monitoring
    • ECG Waves and IntervalsP wave: the sequential activation (depolarization) of the right and left atriaQRS complex: right and left ventricular depolarization (normally theventricles are activated simultaneously)ST-T wave: ventricular repolarization U wave: origin for this wave is not clear - but probably represents"afterdepolarizations" in the ventriclesPR interval: time interval from onset of atrial depolarization (P wave) toonset of ventricular depolarization (QRS complex)QRS duration: duration of ventricular muscle depolarizationQT interval: duration of ventricular depolarization and repolarizationRR interval: duration of ventricular cardiac cycle (an indicator ofventricular rate)PP interval: duration of atrial cycle (an indicator of atrial rate)
    • 1. Impulse from sinus node2. Depolarization of the atria3. Depolarization of the A-V node4. Repolarization of the atria5. Depolarization of ventricles6. Activated state of ventricles immediately after depolarization7. Repolarization of ventricles8. After-potentials following repolarization of ventricles
    • ECG Waves and Intervals
    • Monitoring Leads
    • Basic Rhythm Interpretation• Use a systematic approach• A consistent method will help enhance your assessment, confidence and comfort level.• At CDH, we will use a 10-Step Method to Rhythm Analysis
    • 10-Step Method1. Assess your patient (A, B, C, Ds)2. Assess the heart rate (ventricular & atrial)3. Evaluate the regularity of the rhythm4. Assess the P waves5. Evaluate the PR Interval6. Assess the P:QRS ration7. Evaluate the QRS complex8. Assess the ST segment9. Identify the rhythm10. Determine the clinical significance
    • Mechanisms of Arrhythmias• Abnormal Impulse Formation – Depressed automaticity: bradycardia or escape beats – Increased automaticity: premature beats, tachycardia – Depolarization and triggered activity: ectopic firing• Abnormal Impulse Formation – Block or delay – Re-entry tachycardias (Wolff-Parkinson-White/WPW, A. flutter, A. fib
    • Goals of Antiarrhythmic Drugs• Restore synchrony to myocardial contraction• Suppress abnormal rhythms• Reduce heart rate to maintain cardiac output• As a bridge to ICD, radio-frequency ablation• Match the drugs mechanism of action to the type of arrhythmia
    • Vaughn-Williams Classification of Antiarrhythmics• Class I: Sodium Channel Blockers – Ia: Prolong refractory period – Ib: No change or shorten the refractory period – Ic: Prolongation of the refractory period• Class II: Beta-adrenergic Receptor Blockers• Class III: Potassium Channel Blockers – Prolong action potential duration & refractoriness• Class IV: Calcium Channel Blockers• Others: Digoxin, Adenosine, Magnesium
    • Questions and Comments Questions and Comments