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Deflection deflection deflection deflection moving

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Unformatted text preview: g 25% is utilized as work which is broken down into: –  Pressurization of blood (>99%) –  Acceleration of blood (<1%) 13 Work output of the heart •  Pressurization of the blood (potential energy) –  Moving blood from low pressure to high pressure (volume pressure work or external work) •  The majority of the work (>99%) EKG •  Measures potential difference across the surface of the myocardium with respect to time •  lead-pair of electrodes •  axis of lead-line connecting leads •  transition line-line perpendicular to axis of lead •  Acceleration of blood to its ejection velocity (kinetic energy) –  Out the aortic & pulmonic valves normally accounts for less than 1% of the work component •  Can increase to ~ 50% with valvular stenosis Rate •  Paper speed- 25 mm/sec 1 mm = .04 sec. •  Normal rate ranges usually between 60-80 bps •  Greater than 100 = tachycardia •  Less than 50 = bradycardia •  •  •  •  Intervals PR interval (includes AV nodal delay) should be about .16 sec greater than .20 sec. = 1st degree AV block less than .10 sec. = inadequate delaypossible accessory conduction pathway from atria to ventricle Atrial depol. then a delay then ventricular depol. Total activation time is ~.22 seconds Electrocardiography •  •  •  •  P wave-atrial depolarization QRS complex-ventricular depolarization T wave-ventricular repolarization Atrial repolarization is buried in the QRS complex Leads •  A pair of recording electrodes –  + electrode is active –  - electrode is reference •  The direction of the deflection (+ or -) is based on what the active electrode sees relative to the reference electrode •  Routine EKG consists of 12 leads –  6 frontal plane leads –  6 chest leads (horizontal) Q= first downward R= first upward S= next downward Transition lead The area around the base of the heart is more negative and the area around the apex of the heart is more positive + Axis lead + 14 When the positive terminal is on the right arm, the lead is know as the aVR lead; when on the left arm, the aVL lead and when on the left leg the aVF leadu II I 60* 60* + Eintoven's triangle 60* III + Frontal Plane Leads •  Bipolar limb leads –  Lead I (+ LA -RA) –  Lead II (+ LL - RA) –  Lead III (+ LL - LA) –  AvR (+RA –  AvL (+LA –  AvF (+LL Compliments These 3 leads make a triangle Type of Deflection Wave of Wave of Depolarization Repolarization Moving toward + elect. ⇑deflection ⇓deflection ⇑ deflection ⇓ deflection Moving toward - elect. •  Unipolar limb leads (Augmented ) -LA & LL) -RA & LL) -RA & LA) Einthovens Law- thie sum of lead I and lead IIIequals lead II EKG gives no direct info concerning mechanical performance of the heart as a pump Chest leads are closer to the heart then the limb leads so the results are more accurate Chest Leads (V leads) •  The positive electrodes are on the chest wall –  VI-4th intercostal space- right sternal border –  V2-4th intercostal space-left sternal border –  V3-equidistant between V2 & V4 –  V4-5th intercostal space-mid clavicular line –  V6 left mid axillary line Analysis of EKG •  •  •  •  •  Rate Rhythm & Intervals Axis Hypertrophy Infarction •  The negative (reference) electrode is all limb electrodes hooked together V5 is equidistant betwenn V4 and V6 Rhythm & Intervals Rate •  Tachycardia –  heart rate greater than 105 B/min •  PR interval –  time from SA node to entering the ventricle –  includes the AV nodal delay –  1st degree AV block •  PR interval greater than .2 sec. •  Bradycardia –  heart rate less then 60 B/min •  Prolonged QT interval –  increased incidence of sudden cardiac death •  300-150-100-75-60-50 •  Sinus arrhythmia Not uncommon - heathy sign that the heart is verying its cycle –  longest & shortest RR vary by > .16 sec –  heart rate variability RR interval- from R peak to R peak on an EKG 15...
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