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Ecg 1 Ecg 1 Presentation Transcript

  • Volume Conductor Principles and ECG Rules of Interpretation
    • A wave of depolarization traveling toward a positive electrode results in a positive deflection in the ECG trace .
    • A wave of depolarization traveling away from a positive electrode results in a negative deflection.
    • A wave of repolarization traveling toward a positive electrode results in a negative deflection.
    • A wave of repolarization traveling away from a positive electrode results in a positive deflection.
    • A wave of depolarization or repolarization traveling perpendicular to an electrode axis results in a biphasic deflection of equal positive and negative voltages (i.e., no net deflection).
    • The instantaneous amplitude of the measured potentials depends upon the orientation of the positive electrode relative to the mean electrical vector .
    • The voltage amplitude is directly related to the mass of tissue undergoing depolarization or repolarization
  • Volume Conductor Principles and ECG Rules of Interpretation the last cells in the ventricle to depolarize are the first to repolarize. ATRIUM VENTRICLE
  • American College of Cardiology (ACC)/American Heart Association (AHA) guidelines that: “Recording the resting 12-lead ECG continues to be the most commonly used laboratory procedure for the diagnosis of heart disease.” In addition, “The procedure is safe, simple, and reproducible; the ECG record lends itself to serial studies; and the relative cost is minimal.
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  • Transient current that contributes to phase 4 pacemaker currents in SA and AV nodal cells      T - type ( I Ca - T ) Slow inward, long - lasting current; phase 2 non - pacemaker cardiac action potentials and phases 4 and 0 of SA and AV nodal cells; important in vascular smooth muscle contraction      L - type ( I Ca - L )   Calcium Channels Open in response to Ca ++ influx in vascular smooth muscle      Calcium - activated ( I K, Ca or BK Ca ) Activated by acetylcholine; Gi - protein coupled      Acetylcholine - activated ( I K, ACh ) K ATP channels; inhibited by ATP; therefore, open when ATP decreases during hypoxia; in vascular smooth muscle, adenosine removes the ATP inhibition and opens these channels, producing vasodilation      ATP - sensitive ( I K, ATP ) Phase 3 repolarization of cardiac action potentials      Delayed rectifier ( I Kr ) Contributes to phase 1 of non - pacemaker cardiac action potentials      Transient outward ( I to ) Maintains phase 4 negative potential in cardiac cells      Inward rectifier ( I ir or I K1 )   Potassium Channels " Funny " pacemaker current ( I f ) in cardiac nodal tissue      Slow Na + Phase 0 depolarization of non - pacemaker cardiac action potentials      Fast Na +   Sodium Channels CHARACTERISTICS CHANNEL
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  • Electrocardiographic criteria of right ventricular enlargement
  •   Example #1: (note RAD +120 degrees; RAE; R in V1 > 6 mm; R in aVR > 5 mm)
  •   Example #2: (more subtle RVH: note RAD +100 degrees; RAE; Qr complex in V1 rather than qR is atypical
    •   I. Left Ventricular Hypertrophy (LVH)
    • General ECG features include:
    • QRS amplitude (voltage criteria; i.e., tall R-waves in LV leads, deep S-waves in RV leads)
    • Delayed Intrinsicoid deflection in V6 (i.e., time from QRS onset to peak R is  0.05 sec)
    • Widened QRS/T angle (i.e., left ventricular strain pattern, or ST-T oriented opposite to QRS direction). This pattern is more common with LVH due to pressure overload (e.g., aortic stenosis, systemic hypertension) rather than volume overload.
    • Leftward shift in frontal plane QRS axis
    • Evidence for left atrial enlargement (LAE)
    • ESTES Criteria for LVH ("diagnostic",  5 points; "probable", 4 points)
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    • CORNELL Voltage Criteria for LVH (sensitivity = 22%, specificity = 95%)
    • S in V3 + R in aVL > 24 mm (men)
    • S in V3 + R in aVL > 20 mm (women)
    • Other Voltage Criteria for LVH
    • Limb-lead voltage criteria:
    • R in aVL  11 mm or , if left axis deviation , R in aVL  13 mm plus S in III  15 mm
    • R in I + S in III >25 mm
    • Chest-lead voltage criteria:
    • S in V1 + R in V5 or V6  35 mm
    1 point Delayed intrinsicoid deflection in V5 or V6 (  0.05 sec) 1 point QRS duration 0.09 sec 2 points Left axis deviation 3 points Left Atrial Enlargement in V1   3 points 1 point ST-T Abnormalities : Without digitalis With digitalis 3 points
    • Voltage Criteria (any of) :
    • R or S in limb leads  20 mm
    • S in V1 or V2  30 mm
    • R in V5 or V6  30 mm
    Points + ECG Criteria
  • Example 1 : (Limb-lead Voltage Criteria; e.g., R in aVL >11 mm; note wide QRS/T angle)
  • Example 2 : (ESTES Criteria: 3 points for voltage in V5, 3 points for ST-T changes; also LAE and LAD of -40 degrees; note also the PVC)