WIDE QRS

No P Waves Present

Ventricular Rhythm

no P waves before QRS complexes
  • Regular wide complex tachycardia: 90% ventricular tachycardia
    • ​Dissociated P waves: 100% ventricular tachycardia
    • QRS morphology that does not fit a BBB pattern: almost certainly ventricular tachycardia
  • If rate is ~70, consider pacemaker rhythm: search for pacer spikes
  • < 60/min: ventricular escape (usually 35-40/min) – why? Sinus arrest or AV block
  • 60-120/min: accelerated idioventricular rhythm (reperfusion arrhythmia; cocaine; lytes; ICU)
  •  ≥ 125/min: Ventricular tachycardia
  • With ventricular rhythms, the QRS morphology and ST-Ts should not be further analyzed

P waves Present

Right Bundle Branch (RBBB)

Diagnostic Criteria
  1. QRS ≥ 0.12 s
  2. R is upgoing in V1: triphasic QRS complexes
    –typically rSR’
    –could be M-shaped
    –second upgoing component must be taller and wider than the first
  3. Left leads (I, aVL, V6): deep S waves
  • Bifascicular block = RBBB + left anterior or posterior fascicular block
  • RBBB does not affect the initial QRS forces: search for pathologic Q waves
  • RBBB does not affect the ST segments in the lateral leads:
    • You still need to search for possible ischemia
  • Expected (secondary) repolarization pattern: ST-T usually down in V1; often down in V2, V3 as well​​
CLINICAL SIGNIFICANCE
  • Isolated chronic RBBB has questionable clinical significance
    • ​no work-up is indicated for chronic RBBB
  • New incomplete or complete RBBB
    • chest pain, SOB: consider PE
    • syncope: consider PE
  • STEMI and new RBBB: high-risk condition

Left Bundle Branch

Diagnostic Criteria
  1. Left lead (I, aVL and V5 or V6) QRS is predominantly upgoing​, slow upslope, absence of q waves
  2. Right lead (V1 – V3) QRS is predominantly downgoing, trivial or no R waves
In general, the QRS and ST-T is difficult to analyze in LBBB, but:
  • Pathologic Q waves in the inferior leads may signify remote inferior MI
  • Pathologic Q waves in several lateral leads may signify remote anterior MI
  • ST segment elevation concordant with the QRS complex may signify acute STEMI
  • T-wave inversion concordant with QRS complex (Ts ↓ in V1-V3) may signify ischemia
  • Expected (secondary) repolarization pattern: ST-T axis opposite to QRS axis 
CLINICAL SIGNIFICANCE
  • LBBB is frequently associated with structural heart disease
    • Left axis deviation: left-sided disease
    • Right axis deviation: possibly severe pulmonary hypertension
  • Causes left ventricular dyssynchrony
    • Poor prognostic indicator in CHF
    • Patient may benefit from CRT (BiV pacer)

Wolff-Parkinson-White Pattern

  • short P-R intervals (< 0.11s)
  • delta waves
  • usually does not fit either bundle branch block pattern
  • V1 may be either upgoing or downgoing (upgoing in ~60%)

Rv Paced

  • I, aVL looks like LBBB 
  • all chest leads (including V5 and V6) are downgoing
  • II, III, aVF are downgoing

Biventricular Paced (BiV-paced) 

  • QRS in lead I starts down; QRS in V1 usually upgoing
  • search for pacer spikes and clinical correlation (does the patient have a pacemaker?)​
Picture
BiV Pacing

Nonspecific intraventricular conduction delay

Does not fit any of the above
  • frequently coexists with LAE, 1st degree AV block, atrial fibrillation
  • several causes: review the company it keeps
Causes of IVCD
  • LVH with QRS widening: when LVH criteria are present
  • Periinfarction block: when pathologic Q waves are present
  • Hyperkalemia: when narrow-based peaked T waves are present
  • Hypothermia: when Osborne waves, bradycardia, ST-T abnormalities, long QT are present
  • Drug toxicities: when QT prolongation is present (TCA: deep S in I; tall R’ in aVR)
  • Infiltrative heart disease and connective tissue disease (e.g., amyloidosis, PSS)
Picture
LVH with QRS widening