Ventricular Conduction Disturbances Chapter 7

Bundle Branches Normal conduction speed through the bundles is about 0.1 seconds

Bundle Branch Block Right Left Consider a blocked or slowed branch or bundle Right Left

Right Bundle Branch Block First Phase will be normal Second Phase - Normal Third Phase - ? After the left ventricle has completely depolarized, the right ventricle continues to depolarize

Right Bundle Branch Block 1. 2. 3. 1. r wave in V1 q wave in V6 2. S wave in V1 R wave in V6 3. R’ wave in V1 S wave in V6

Right Bundle Branch Block Criteria V1 or V2 = rSR’ - “M” or rabbit ear shape V5 or V6 = qRS Large R waves Right chest leads: T wave inversion (“secondary changes” since they reflect a delay in depolarization not an actual change in depolarization). Complete RBBB: QRS > 0.12 sec. Incomplete RBBB: QRS = 0.10 to 0.12 sec.

Right Bundle Branch Block V1 = rSR’ V6 = qRS

Right Bundle Branch Block V2 = rSR’ V6 = qRS

Right Bundle Branch Block Clinical Significance Healthy heart Organic heart disease atrial septal defect pulmonary disease valvular lesions degenerative changes in conduction system chronic coronary artery disease pulmonary embolism after bypass graft surgery Permanent or transient RBBB by itself requires no treatment

Left Bundle Branch Block RBBB affects mainly the terminal phase of depolarization LBBB affects the early and terminal phases of depolarization Septum is depolarized from right to left (rather than left to right) Depolarization of the left ventricle takes longer

Left Bundle Branch Block 1. r wave in V1 R wave in V6 2. S wave in V1 R wave in V6

Left Bundle Branch Block Loss of septal R in V1 and septal Q in V6. Wide QRS Negative in V1 Positive in V6

Left Bundle Branch Block Criteria Wide QRS complex V1 = QS (or rS) and may have a “W” shape to it. V6 = R or notched R showing a “M” shape or rabbit ears Secondary T wave inversion Secondary if in lead with tall R waves Primary if in right precordial leads

Left Bundle Branch Block

RBBB versus LBBB ? ?

Left Bundle Branch Block Causes long standing hypertension valvular lesion cardiomyopathy coronary artery disease Precursor Advanced CAD Valvular heart disease Hypertensive heart disease Cardiomyopathy

Rate-Related (Exercise-Induced) Bundle Branch Blocks Ischemia or other factors during exercise may produce BBB not seen at rest Rate-limited bundle branch block Exercise induced bundle branch block

Incomplete Bundle Branch Blocks RBBB or LBBB where QRS is between .10 and .12 with same QRS features Incomplete RBBB normal variant Incomplete LBBB a progression of LVH

Intraventricular Delay or Intraventricular Conduction Defect General term for wide QRS complexes that are not typical of RBBB or LBBB

Pacemaker Pattern

Pacemaker Patterns

Trifascicular Conduction System

Tri-fascicular Conduction System Right bundle Left anterior (superior) fascicle Left posterior (inferior) fascicle Fascicular block (or hemiblock) = a block in either the LAF or LPF.

Fascicular Blocks Fascicular blocks only slightly prolongs the QRS. Fascicular blocks cause axis deviation as do infarcts and hypertrophy. Left or right axis deviation without signs of infarct or hypertrophy are fascicular blocks.

Left Anterior Fascicular Block Limb leads QRS less width less than 0.12 sec. QRS axis = Left axis deviation (-45° or more) if S wave in aVF is greater than R wave in lead I small Q wave in lead I, aVL, or V6

Left Posterior Fascicular Block Right axis deviation (QRS axis +120° or more) S wave in lead I and a Q wave in lead III (S1Q3) Rare

Bifascicular Block Two of the three fascicles are blocked. Most common is RBBB with left anterior fascicular block.

Summary The last component of the QRS vector will be shifted in the direction of the last part of the ventricles to be depolarized. In other words, the major QRS vector shifts toward the regions of the heart that are most delayed in being stimulated. RBBB: late QRS forces point toward the right ventricle (Rabbit ears, M shape in V1) LBBB: late QRS forces point toward the left ventricle (negative in V1 and R or notched R in V6) LAFB: late QRS forces point in a leftward and superior direction (LAD with deep S wave in aVF ).

Hypertrophy In The Presence of Bundle Branch Block RVH and RBBB RAD is typically seen; also look for RAE and its peaked P waves. RBBB with RAD indicates RVH is likely present, too. LVH and RBB usual criteria can be used but also look for LAE