4. Wave, IntervalDuration (msec) P wave duration<120 PR interval120-200 QRS duration<110-120 QT interval (corrected) ≤440-460

7. Retrograde P waves precede onset of the QRS complex. AV junctional rhythm, rate approx. 50 min. Retrograde P wave follows each junctional discharge.

8. A short episode of atrial flutter is followed by 5 seconds of asystole before a junctional escape rhythm resumes. The patient became presyncopal at this point. Intermittent sinus arrest with junctional escape beats at irregular intervals (red circles)

10. ATRIOVENTRICULAR BLOCK (AV Block)

12.  Mobitz type I (2:1)  Mobitaz type II (Wenkebach)

19. 1. Left BUNDLE BRANCH BLOCK (LBBB)

22.  Basic requirements include a prolonged QRS duration to 120 milliseconds or beyond; broad and commonly notched R waves in leads I, aVL, and the left precordial leads; narrow r waves followed by deep S waves in the right precordial leads; and absent septal q waves. R waves are typically tall and S waves are deep.

24.  The ST-T waves are, as in LBBB, discordant with the QRS complex, so that T waves are inverted in the right precordial leads (and other leads with a terminal R′ wave) and upright in the left precordial leads and in leads I and aVL.

26.  QRS duration ≥ 120 msec  Broad, notched R waves (rsr′, rsR′, or rSR′ patterns) in right precordial leads (V 1 and V 2 )  Wide and deep S waves in left precordial leads (V 5 and V 6 )

28. RBBB with acute anterior MI. Loss of anterior depolarization forces results in QR-type complexes in the right to mid precordial leads, with ST elevations and evolving T wave inversions (V 1 to V 6 ).

29. LBBB with acute inferior MI. Note the prominent ST segment elevation in L II, III, and aVF, with reciprocal ST segment depression in I and aVL superimposed on secondary ST-T changes. The underlying rhythm is AF.

30. With uncomplicated left bundle branch block, early septal forces are directed to the left. Therefore, no Q waves will be seen in leads V 5 and V 6 With left bundle branch block complicated by anteroseptal infarction, early septal forces can be directed posteriorly and rightward

31. Therefore, prominent Q waves may appear in V 5 and V 6 as a paradoxical marker of septal infarction (right panel)., Anterior wall infarction (involving septum) with left bundle branch block. Note the presence of QR complexes in leads I, aVL, V 5, and V 6.

32. Unifascicular Blocks

33.  The most characteristic finding is marked left axis deviation. However, LAFB is not synonymous with left axis deviation.  Axis shifts to between -30 and -45 degrees commonly reflect other conditions, such as LVH, without conduction system damage and such patterns are best referred to as left axis deviation rather than as LAFB.

35.  Frontal plane mean QRS axis of -45 to - 90 degrees  rS patterns in leads II, III, and aVF and a qR pattern in lead aVL  QRS duration <120 msec

37.  Frontal plane mean QRS axis >120 degrees  RS pattern in leads I and aVL with qR patterns in inferior leads  QRS duration < 120 msec  Exclusion of other factors causing right axis deviation (e.g., right ventricular overload patterns, lateral infarction)