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Physiology Objectives 4 1. Dipole: a separation of charge between which current can flow Picture of heart with depolarization wave, vectors, and ECG correlates: 2. Leads (- to +) and ECG dipole conventions: I (RA to LA): II (RA to LL): III (LA to LL): aVF (virtual to LL): aVL (virtual to LA): aVR (virtual to RA): V1: V2 (virtual to floor (90o)): V3: V4: V5: V6 (virtual to RA (0o)): 3. ECG with waves and intervals labeled: Wave: an event that starts and ends at 0 volts P wave: 0.05-0.10 sec Q wave: first negative event before R wave R wave: first positive wave of ventricular depolarization S wave: first negative event after R wave T wave: 0.15 sec Segment: an event that begins at one wave and stops before the next ST segment: 0.10 sec TQ segment: 0.60 sec o Note: recall that this is a segment because the Q and T waves are in the ventricle while the P wave is in the atrium! Interval: an event that includes a segment and one or more waves PR interval: 0.12-0.20 sec QT interval: 0.31 sec Complex: an event that includes more than one wave with no segments QRS complex: 0.06-0.10 sec 4. ECG with timing of activation through heart: 5. Given data, determine axis of depolarization: Draw perpendicular lines from the heads of leads I, II, and III. These lines will intersect and form a triangle. The vector from the origin to the center of the newly drawn triangle is the axis of depolarization. 6. 1o heart block: P wave conduction to AV node is long a. PR interval longer than 0.20 sec 2o heart block: some P wave conduction to AV node does not occur a. Mobitz type I: PR intervals of increasing length until reset when a P wave is not followed by a QRS complex b. Mobitz type II: multiple P waves followed by a single QRS complex; named in ratios (X P waves followed by a QRS complex is called X:1 block) o 3 heart block: no P wave conduction to AV node a. Large QRS complexes not associated with P waves Conditions needed for reentrant arrythmia: a divergent pathway and a unidirectional block; this causes reentrant arrythmia because the wave of depolarization can complete a circuit around the divergent path