ECG Conduction Defects
Sinoatrial Block
Bundle Branch Blocks
Fascicular Blocks
– Left axis deviation (-45 to -90 degrees)
– qR complexes in lateral leads I, aVL
– rS complexes in inferior leads II, III, aVF
– QRS duratrion prolonged but < 120 ms (0.12 sec)
– Prolonged R wave peak time in aVL > 45ms
– Right axis deviation (RAD) (+90 to +180 degrees)
– rS complexes in lateral leads I and aVL
– qR complexes in inferior leads II, III and aVF
– QRS duratrion prolonged but < 120 ms (0.12 sec)
– Prolonged R wave peak time in aVF
– RBBB + LAFB masnifest as left axis deviation
– RBBB + LPFB masnifest as right axis deviation”
AV block
– PR interval > 0.2 sec (> 200 ms or > 1 large square)
– Constant 1:1 P-wave-to-QRS-complex ratio is maintained
– Progressive PR interval prolongation with each beat until a P wave is dropped
– Irregular R-R interval
– May demonstrate feature of ‘group beating’
– Narrow QRS complexes in most cases
– Usually improves with atropine
– Can be either Mobitz I or Mobitz II
– Regular R-R interval between conducted beats
– Can be 2:1, 3:1 or 4:1
– If Mobitz I, telemetry may show runs of PR prolongation intermittently
– Improves with atropine if Mobitz I and worsens if Mobitz II
– Another clue to differentiate is QRS duration, narrow QRS is usually seen in Mobitz I
– Intermittent non-conducted P waves
– Fixed PR interval in conducted beats (no prolongation as seen in Mobitz I)
– P-P interval is constant
– R-R interval surrounding the dropped beat is multiple of conducted beats R-R interval
– Either no pattern of conduction block or fixed ratio block such as 2:1, 3:1 etc.
– Broad QRS complex is usually seen
– Can worsen into complete heart block
– Complete AV dissociation
– P and QRS complexes occur independent of each other
– Regular P-P interval
– Regular R-R interval
– More P waves than QRS complexes
– Ventricular rhythm maintained by either junctional escape or ventricular escape rhythm
– Can present with ventricular standstill without escape rhythm