Last updated 11/9/26
Below is an ECG Exercise focused on bundle branch blocks and hemiblocks (part of the Self-Study Curriculum). ECGs are from Garcia, 12-Lead ECG: The Art of Interpretation, Chapter 13.
Right Bundle Branch Block
What are the three main criteria for RBBB? - QRS ≥ 0.12 s (if one lead is ≥ 0.12 s, the whole ECG is - intervals are the same in every lead)
- Slurred S wave in I and V6
- RSR' pattern in V1 (R' taller than R)
Which RBBB criterion should you look at first, and why? - The slurred S in I and V6 - Garcia considers it the most important criterion
- V1 has countless variations (rSR', qR', RR', rsR'R'') and will fool you if you start there
- Whatever the shape, V1 should be predominantly positive with an increased R:S ratio
What does a qR' complex in V1 mean in a patient with RBBB? - The initial R has been replaced by a Q wave = old or new anteroseptal infarct
- The first positive wave is then called R'
ECG 1
[Insert image - Garcia ECG 13-1]
What is the etiology of the increased R:S ratio in V1/V2? - RBBB - slow cell-to-cell conduction through the RV produces a late, unopposed rightward vector
- The right precordial leads (V1-V3) show the greatest change
Which findings confirm RBBB? - QRS ≥ 0.12 s
- Slurred S waves (slow downstroke and upstroke) in I and V6
- Classic rSR' ("rabbit ears") in V1
Lead III also shows an rSr'. What can cause this without a bundle branch block? - An isolated, regional intraventricular conduction delay
ECG 2
[Insert image - Garcia ECG 13-2]
- RBBB - the slurred S waves make the diagnosis
Describe the complex in V1. - An rsR'R'' pattern: a tiny rs, then an R', then the tallest peak R''
- No true S wave between R' and R'' - still a variant of the rabbit-ear pattern
What is the QRS axis? Is a hemiblock present? - Left axis (up in I, down in aVF)
- Left anterior hemiblock - with the RBBB this is a bifascicular block
ECG 3
[Insert image - Garcia ECG 13-3]
Identify features of RBBB. - Obvious slurred S waves
- Bizarre complex in V1
- V2 shows clearer notching and RSR' morphology than V1
Is there evidence of ischemia? - Yes - inferolateral ischemia
- III and aVF: T waves are concordant with the terminal QRS
- Lateral leads: T wave flattening
Where should the ST segments be in an uncomplicated RBBB? What ST change is worrisome? - On the baseline; ST depression in the right precordial leads is common
- ST elevation in the right precordial leads with RBBB is consistent with AMI
What is the clinical significance of RBBB? - Usually associated with CAD, but can be a benign finding in young people
- Incomplete RBBB (RSR' in V1/V2 without QRS widening) may progress to complete RBBB with age
ECG 4
[Insert image - Garcia ECG 13-4]
The QRS is clearly ≥ 0.12 s. What is your differential? - RBBB
- LBBB
- IVCD
- PVC / ventricular rhythm or aberrantly conducted beat
- Ventricular beats and rhythms usually take an RBBB or LBBB shape too - use "the company it keeps"
Identify features of RBBB. - V1 is a qRR' complex - easy to misread if you look at V1 alone
- Slurred S waves in I and V6 confirm RBBB
ECG 5
[Insert image - Garcia ECG 13-5]
Identify features of RBBB. - Meets all criteria easily: wide QRS, rSR' in the right precordial leads, slurred S in I and V6
There is a small notch at the bottom of the QRS in lead I. Is it concerning? - No - it is part of the QRS; it lines up with the r wave of the Qr complex in lead III
- Verify with a straight edge - always investigate small oddities, but this one is benign
Are there signs of ischemia? - Slight ST elevation in III, with ST depression in the reciprocal and lateral leads
- Use calipers - a wide QRS can create an "optical illusion" of ST changes; here the changes are real
- Minimal but troubling because they are reciprocal - needs strong clinical correlation
ECG 6
[Insert image - Garcia ECG 13-6]
Identify features of RBBB. - QRS ≥ 0.12 s
- Slurred S waves in I and V6
- rSR' in V1
What is the QRS axis? Is a fascicular block present? - Left axis - left anterior hemiblock
- RBBB + LAH = bifascicular block
Can you diagnose LVH in RBBB? In LBBB? - RBBB: yes - use the usual criteria (here the R in aVL is > 11 mm = LVH)
- LBBB: no - LVH criteria do not apply
Can you diagnose RVH or RAE in RBBB? - RVH: very difficult, if not impossible (a tall R in V1 is not reliable)
- RAE: yes, by the usual criteria - may raise suspicion of RVH; confirm with echo
ECG 7
[Insert image - Garcia ECG 13-7]
- Notched, positive complex at the top of the QRS in V1 = RR' pattern
- Slurred S waves in I and V5-V6
Is there an S wave in V1? Is this technically an RSR'? - No - an S wave must dip below the baseline
- Calling it RSR' is technically wrong but clinically irrelevant
Why is the R' taller than the first R in RBBB? - The LV depolarizes normally via the left bundle first
- The RV is depolarized late by slow cell-to-cell spread - that late vector is unopposed, giving the tall R' and slurred S
Notched positive complexes also occur in LBBB. How do you tell them apart? - RBBB: notched positive complex in V1
- LBBB: notched positive complex in V5-V6; V1-V2 primarily negative
ECG 8
[Insert image - Garcia ECG 13-8]
- NSR - a P wave precedes each QRS
Is the QRS narrow or wide? Why is the P wave reassuring here? - Wide - very wide, small complexes
- QRS ≥ 0.16 s could be a ventricular focus (escape rhythm or VT); a P before each QRS argues for a supraventricular origin
What type of bundle branch block is this? - RBBB - slurred S waves and rsR' in V1
Identify the pathologic Q waves. - Classic, very wide Q waves in the inferior leads = inferior wall MI
Is this RBBB + left posterior hemiblock? - Cannot officially call it - LPH is a diagnosis of exclusion and usually shows a qR in III; this is a QR from the IWMI
- The wide, slurred R' in V1 often seen with LPH is present - clinically, consider a possible bifascicular block
ECG 9
[Insert image - Garcia ECG 13-9]
What bundle branch block is present? - RBBB - V1 alone does not give it away
- Slurred S waves in I and V6, clinched by the increased R:S ratio in V1
What's going on in the 2nd, 4th, and 6th beats? - Wide (but not very wide) aberrant beats in a bigeminal pattern
- Supraventricular bigeminy with aberrancy
How do you know the aberrant beats are supraventricular and not PVCs? - The first 0.03 s of the aberrant and normal complexes are identical
- Both travel down the AV node and only split before the bundle branches
What other wave is visible? ECG 10
[Insert image - Garcia ECG 13-10]
Identify findings suggestive of RBBB. - Slurred S waves in I and V6 (small, but slurred)
- Classic rSR' in V1
What are the abnormal complexes in beats #1, #3, #5? - PACs with aberrancy - premature P waves precede them
- Rhythm: supraventricular bigeminy; use the rhythm strip to sort normal from aberrant beats
Look at the T waves. What is abnormal? - T waves are concordant in every lead except I, aVL, aVR, and V2
- Diffuse T wave abnormality: ischemia, CNS event, or other causes
RBBB is usually stable. Why does it matter whether it is new? - A new RBBB can herald infarction or other impending problems - always find an old ECG
Left Bundle Branch Block
What are the three main criteria for LBBB? - QRS ≥ 0.12 s
- Broad, monomorphic R waves in I and V6, with no Q waves
- Broad, monomorphic S wave in V1 (a small r wave is allowed)
- "All up or all down" - like a rock thrown in the air
What is concordance and why does it matter in a bundle branch block? - Normally the ST segment and T wave point opposite to the terminal QRS (discordant)
- Concordant ST/T (same direction as the terminal QRS) suggests underlying pathology such as ischemia
What can and cannot be diagnosed in the presence of LBBB? - Cannot: LVH or RVH (complex size reflects the abnormal, unopposed conduction)
- Can: atrial enlargement by the usual criteria; infarction (covered in the AMI chapter) using concordance
- Axis: usually normal or left; rarely right (LBBB + RVH)
ECG 11
[Insert image - Garcia ECG 13-11]
What type of bundle branch block is this? - Classic LBBB
- QRS > 0.12 s; broad monomorphic complexes - all up in V6, all down in V1
Why do leads I and V6 look so similar? - Both electrodes sit at the same point in 3-D space (left side, mid-axillary line) where the frontal and horizontal planes intersect
- Small differences come from imperfect lead placement
What is the QRS axis? (normal, left, right, extreme) - Left axis - LBBB is usually normal or left
- Rarely right, when LBBB is combined with RVH
An ECG looks wide, bizarre, and ugly. What are the two most likely causes? - LBBB
- IVCD from hyperkalemia
ECG 12
[Insert image - Garcia ECG 13-12]
Identify features of LBBB. - All criteria met, starting with a wide QRS
- Notching in the lateral leads (I, aVL, V5-V6) creates an RR' pattern
The RR' notching could be mistaken for rabbit ears. Why is this not RBBB? - The notching is in V5-V6, not V1
- RBBB requires rabbit ears in V1 plus slurred S waves in I and V6
Identify findings suggestive of atrial enlargement. - LAE - meets both P-mitrale and the large negative terminal P component in V1
Identify findings suggestive of LVH. - Cannot be assessed - in LBBB the complex size reflects the abnormal, unopposed LV depolarization
ECG 13
[Insert image - Garcia ECG 13-13]
- QRS ≥ 0.12 s (narrower than ECG 12, but still qualifies)
- All up or all down: rS in V1 (common in LBBB), monomorphic R in V6
- Notching in I and V5-V6
Look closely at V6. Is that a delta wave? - No - it is not seen in any other lead
- It is a late intrinsicoid deflection, common in LBBB and LVH
ECG 14
[Insert image - Garcia ECG 13-14]
- The precordial leads (V1-V5) are easily mistaken for LVH
- But LVH should be < 0.12 s - these complexes are wide = LBBB
- Notching in V6 and wide limb lead complexes also fit LBBB
The limb leads look narrower. Can the QRS width differ between leads? - No - intervals are the same throughout the ECG; if one lead is ≥ 0.12 s, they all are
- Avoid snap judgments
ECG 15
[Insert image - Garcia ECG 13-15]
- QRS ≥ 0.12 s
- S wave dominant in V1/V2
- Monophasic notched R in I, V6
Identify findings consistent with atrial enlargement. - P-pulmonale in lead II (RAE)
- LAE in V1
- = Biatrial enlargement
What is the 4th complex from the end? - Looks like a PJC with aberrancy, but its axis and terminal portion differ from the native beats - PJC very unlikely
- Most likely a PVC from a ventricular focus off the usual depolarization path
ECG 16
[Insert image - Garcia ECG 13-16]
Identify findings that suggest LBBB. - Wide QRS, rS in V1, monomorphic R in V6
- Left frontal axis
What is the rhythm and rate? Identify findings that suggest atrial enlargement. The QT looks long. Is this significant? - QT prolongation is common in BBB (especially LBBB) - slow cell-to-cell depolarization and repolarization
- It does not carry the same significance as a long QT without a block
What are common causes of LBBB? - Hypertension
- Coronary artery disease
- Dilated cardiomyopathy
- Rheumatic heart disease
- Infiltrative diseases of the heart
- Benign or idiopathic causes
- Most are due to HTN, CAD, or both
ECG 17
[Insert image - Garcia ECG 13-17]
Identify findings that suggest LBBB. - QRS ≥ 0.12 s - the first step; miss the width and you miss the diagnosis
- rS waves in V1-V2
- Monophasic notched R wave in I, aVL, V5-V6
Abnormal Q waves in the inferior leads with LBBB - block or old infarct? - Inferior Qs can be due to LBBB alone, but still consider an old IWMI
- Q waves in the lateral or high lateral leads are pathologic = old infarct
ECG 18
[Insert image - Garcia ECG 13-18]
Identify findings suggestive of LBBB. - QRS ≥ 0.12 s
- rS waves in V1-V2 (predominantly negative)
- Monophasic notched R wave in I, aVL, V6
What is unusual about the QRS in the limb leads and V5? - Multiple notches in the limb leads; a small peak right after the P wave in V5
- Measure: all of these fall within the QRS - cause unclear, not a separate wave
Quick match: RBBB, LBBB, or both? - Slurred S wave - RBBB
- QRS ≥ 0.12 s - Both
- rS complex in V1 - LBBB
- Increased R:S ratio in V1 - RBBB
- Axis in the right or left quadrant - Both
ECG 19
[Insert image - Garcia ECG 13-19]
What is the rhythm? Are P waves present? - Small, wide, almost imperceptible P waves in V1-V3
Identify findings that suggest LBBB. - QRS ≥ 0.12 s
- No slurred S waves in I and V6
- Monomorphic complexes, all up or all down, in I, V1, and V6
Is the hump in lead III a P wave with first-degree AV block? - No - measure it: it is part of a biphasic T wave
What is the axis? Can LBBB shift the axis by itself? - Left axis - common in LBBB
- Current belief: yes - initial LV activation from the posterior wall mimics LAH (left axis); from the anterior wall or both walls gives a normal or rightward axis
ECG 20
[Insert image - Garcia ECG 13-20]
Identify findings that suggest LBBB. - QRS ≥ 0.12 s
- Monomorphic S wave or rS complex in V1
- Monomorphic R wave in I and V6
What is the underlying rhythm? What about the PR interval? - Sinus - P waves map out and the PR is constant for the native beats
- First-degree AV block
What are the 2nd, 4th, and 5th beats from the left? - Aberrant compared with the native QRS - PVCs, or PJCs with aberrancy
- The 5th beat appears to come from a different focus - at least two ventricular foci possible
Is this ventricular tachycardia? - No - there is no AV dissociation, a mandatory criterion for VT
Why is there no compensatory pause after the ectopic beats? - The diseased AV node (note the first-degree block) blocks retrograde conduction, so the sinus node is not reset
Intraventricular Conduction Delay (IVCD)
What is the difference between a localized and a generalized IVCD? - Localized: a multi-peaked complex (RSR'-like) in one lead, not ≥ 0.12 s - very common in lead III
- Generalized: QRS ≥ 0.12 s throughout, but not fitting RBBB or LBBB (often LBBB-like in V1, RBBB-like in V6)
You see a QRS ≥ 0.12 s. What four possibilities should you consider, and what is your next thought? - LBBB
- RBBB
- IVCD
- Ventricular or aberrantly conducted beats
- Looks like an IVCD: think hyperkalemia and treat
- Looks like VT: treat immediately
ECG 21
[Insert image - Garcia ECG 13-21]
- QRS > 0.12 s, so it is a block of some kind
- Slurred S in I and V6 like RBBB - but no increased R:S ratio in V1
- S wave / rS in V1/V2 like LBBB - but no monophasic R in I or V6
- Fits neither = IVCD
What medical emergency should you be worried about? - Hyperkalemia - the most common cause of IVCD
- Once an IVCD appears, you may have only minutes - this patient arrested less than 5 minutes after this ECG
What other findings support hyperkalemia? - PR prolongation
- Tall, broad T waves
- Widening of the entire complex, including the QRS
- Associated hypocalcemia - hyperkalemia plus hypocalcemia is common in ESRD patients on dialysis
- Treat rapidly, before progression to a sine wave or asystole
ECG 22
[Insert image - Garcia ECG 13-22]
- No P waves precede any complex
- The baseline wavering is artifact - it is not consistent even within the same lead
What is the QRS morphology? - Much wider than 0.12 s and matches neither RBBB nor LBBB = IVCD
What diagnosis should you be worried about? - Severe hyperkalemia - bordering on a sine wave pattern
- The patient was treated and the ECG changes reversed
What else is on the differential? How does the QT help? - Accelerated idioventricular rhythm
- Both AIVR and this degree of hyperkalemia would usually prolong the QT - the normal QT here is unusual
ECG 23
[Insert image - Garcia ECG 13-23]
- Ventricular paced rhythm - small pacer spikes before each QRS
Why are the paced complexes wide and bizarre? - The lead tip sits on the interventricular septum and acts like an ectopic ventricular focus
- Depolarization spreads cell-to-cell, often producing an LBBB, RBBB, or IVCD pattern
Left Anterior Hemiblock (LAFB)
What are the criteria for left anterior hemiblock? - Left axis deviation, -30 to -90°
- qR complex or an R wave in lead I
- rS complex in lead III (and probably II and aVF)
What is the 2-second shortcut for LAH? - Lead I positive + aVF negative = left quadrant
- Then look at lead II: positive = 0 to -29° (benign); negative = -30 to -90° = LAH
Can you call LAH in a patient with an inferior MI? - Purists say no (inferior Q waves replace the small r waves)
- Garcia: a -30 to -90° axis is still abnormal - better to overcall LAH than miss a bifascicular block in an AMI
ECG 24
[Insert image - Garcia ECG 13-24]
Determine the quadrant (normal, left, right, extreme) of the electrical axis. - Left quadrant - positive in I, negative in aVF
Is the left axis benign or pathologic? How do you tell quickly? - Look at lead II: here it is negative, so the axis is -30 to -90° = pathologic
What are the criteria for diagnosing left anterior fascicular block? - Left axis deviation, -30 to -90° (shortcut: left quadrant and lead II negative)
- qR complex or R wave in lead I
- rS complex in lead III (probably also II and aVF)
- Yes - meets all criteria
- Left quadrant with negative lead II
- qR or R in lead I
- rS in lead III - the r is tiny; use a magnifying glass
ECG 25
[Insert image - Garcia ECG 13-25]
Determine the quadrant (normal, left, right, extreme) of the electrical axis. - Left quadrant - positive in I, negative in aVF; lead II is negative
- Yes - meets all criteria
- Axis -30 to -90° (lead II negative)
- qR in lead I
- rS in lead III (the r is easier to see here - size does not matter, only presence)
Where is the precordial transition? - Between V5 and V6 - V2-V5 are still negative (clockwise rotation)
ECG 26
[Insert image - Garcia ECG 13-26]
Determine the quadrant (normal, left, right, extreme) of the electrical axis. - Left quadrant - positive in I, negative in aVF
- Yes - meets all LAH criteria
What do you notice about the voltage? - Very low voltage - misses the low-voltage (effusion) criterion by only ~1 mm; lead II is 5-6 mm
Why does the QRS height in lead II vary from beat to beat? - Respiratory variation - small axis shifts with breathing
- Typical of obese patients: small complexes and a more horizontal heart
Left Posterior Hemiblock (LPFB)
What are the criteria for left posterior hemiblock? - Axis 90 to 180° (right quadrant - not extreme right)
- S wave in lead I and q wave in lead III
- Exclusion of RAE and/or RVH
- LPH is a diagnosis of exclusion
Why is LPH rare, and what should a right axis make you ask? - The posterior fascicle fans out broadly - it takes a large lesion to block it
- RVH is the most common cause of a right axis, so exclude it (and RAE) first
- Every right axis: ask "Is this LPH?" - if you don't think of it, you will miss it
ECG 27
[Insert image - Garcia ECG 13-27]
Determine the quadrant of the electrical axis (normal, left, right, or extreme). - Right - down in I and up in aVF (plain right quadrant, not extreme)
What are the criteria for diagnosing left posterior fascicular block (LPFB)? - Right axis
- S wave in lead I and q in III
- Exclusion of RAE and/or RVH
Does this meet criteria for LPFB? - Yes - right axis, S in I, small Q in III
- No RAE or RVH
What besides RVH can cause an abnormal right axis? - An extensive lateral wall MI - dead lateral myocardium shifts the vector rightward
How do you distinguish LPH from an S1Q3T3 pattern? - S1Q3T3 = S in I, Q/q in III, inverted T in III; seen in ~15-30% of PE (acute RV strain)
- The ECG often cannot tell them apart - you need the history and exam
- This patient had no evidence of PE, so this is LPH
ECG 28
[Insert image - Garcia ECG 13-28]
- Sinus tachycardia (pretty severe)
Determine the quadrant of the electrical axis (normal, left, right, or extreme). - Right - between 90 and 180°
- Yes - right axis, S in I, small q in III
- No RAE; the only RVH criterion is the right axis (no increased R:S in V1)
- No inverted T in III, so the S1Q3T3 is incomplete
What could be causing the tachycardia? - PE or another source - correlate with the history
What other findings are troubling? - QT prolongation
- Tall, nearly symmetrical T waves in many leads
What is the differential for these combined findings? - Ischemia (CAD is the most common cause of LPH)
- Hemorrhagic shock with hypocalcemia after massive transfusion
- Pulmonary embolus
- CHF in an ESRD patient
- All are life-threatening - clinical correlation required
ECG 29
[Insert image - Garcia ECG 13-29]
Determine the quadrant of the electrical axis (normal, left, right, or extreme). - Right - down in I and up in aVF
- Yes - S in I, small q in III, right axis
Which exclusion criteria did you check, and do any apply? - Tall P wave - but it does not reach the 2.5 mm P-pulmonale threshold
- Late clockwise transition - but no Q waves to suggest an old lateral MI
- No RVH
- None apply
There is an S1Q3T3 pattern. Is this a PE? - Must be addressed clinically, but there is no tachycardia as you would expect with PE
- S1Q3T3 is suggestive, not pathognomonic, of PE
ECG 30
[Insert image - Garcia ECG 13-30]
Does this ECG meet the basic criteria for LPFB? - On the surface, yes: S in I, q in III, right axis
- No - LPH is a diagnosis of exclusion
- RAE: P wave ≥ 2.5 mm tall in lead II (P-pulmonale)
- RVH: very early counterclockwise transition with a markedly increased R:S in V1
What explains the S1Q3T3 pattern here? Quick match: LAH, LPH, both, or neither? - Axis -30 to -90° - LAH
- Axis 90 to 180° - LPH
- q wave in lead I - LAH
- q wave in lead III - LPH
- Diagnosis of exclusion - LPH
ECG 31
[Insert image - Garcia ECG 13-31]
- LPFB - right axis, S in lead I, q in lead III
- No RAE or RVH - no exclusion criteria
Why is LPH so often missed? - It is rare by itself, so even advanced readers forget it
- Every axis of 90-180°: ask "Is this LPH?"
- Yes - a likely cause of the LPH is an acute inferior wall MI
- ST elevation in the inferior leads with reciprocal changes in the high lateral leads
- Minimal ST elevation in the lateral precordial leads - hard to call alone, but "the company it keeps" makes it suspicious
Bifascicular Blocks
What is a bifascicular block? - RBBB plus either LAH or LPH (three fascicles: right bundle, left anterior, left posterior)
- RBBB-LAH: slurred S in I and V6, rabbit ears in V1, QRS ≥ 0.12 s, axis -30 to -90°, rS in III
- RBBB-LPH: RBBB pattern, right axis, small q in III
Which bifascicular block is more dangerous? - RBBB-LAH: stable chronically; in an acute MI, loss of the remaining posterior fascicle can cause complete heart block - indication for acute pacing
- RBBB-LPH: unstable - the thin, cord-like anterior fascicle is easily knocked out; often progresses to complete heart block, especially in AMI
Can an AV block and a bundle branch block coexist? - Yes - AV blocks come from the AV node; BBBs from the bundles/fascicles
- e.g., first-degree AV block with a bifascicular block, or second/third-degree block with LBBB
ECG 32
[Insert image - Garcia ECG 13-32]
Is the QRS interval normal, short, or long? Is this a LBBB, RBBB, or IVCD? - Slurred S waves in I and V6
- Increased R:S ratio in V1 / RSR' in V1-V2
- = RBBB
Determine the electrical axis. Which fascicular block is present? - Left quadrant (positive in I, negative in aVF); lead II negative = -30 to -90°
- rS in III, qR / R in I
- Left anterior fascicular block - with the RBBB = bifascicular block (RBBB-LAH)
- RBBB-LAH is usually stable and rarely progresses to complete heart block
- Exception: an AMI in progress - ischemia of the remaining posterior fascicle can cause complete heart block
- RBBB-LAH with an acute MI = indication for acute pacemaker placement, before the patient decompensates
ECG 33
[Insert image - Garcia ECG 13-33]
Is this a LBBB, RBBB, or IVCD? - QRS ≥ 0.12 s
- Slurred S waves in I and V6; increased R:S ratio in V1 / RSR' in V1-V2
- = RBBB
Determine the electrical axis. Which fascicular block is present? - Left quadrant; lead II negative = -30 to -90°
- rS in III, qR / R in I
- LAFB = bifascicular block (RBBB-LAH)
Lead I is positive with a slurred S wave. What are the two possibilities? - RBBB with a normal axis
- Bifascicular block (RBBB-LAH)
ECG 34
[Insert image - Garcia ECG 13-34]
- Irregularly irregular with no P waves = atrial fibrillation
- The wide complexes are conducted with RBBB-LAH morphology - not polymorphic VT
Which bundle branch and fascicular blocks are present, if any? - RBBB: QRS ≥ 0.12 s, increased R:S in V1/V2, slurred S in I and V6
- LAFB: left axis, negative in II, rS in III, qR in I
- = Bifascicular block
Does the AF change the stability of the bifascicular block? - No - RBBB-LAH stays stable unless there is an acute ischemic event
ECG 35
[Insert image - Garcia ECG 13-35]
- Normal sinus rhythm, ~80 bpm
The QRS is wide (≥ 0.12 s). Is there a LBBB, RBBB, or IVCD? - RBBB - slurred S waves in I and V6, rsR' in V1
What quadrant does the electrical axis lie in? Is there a fascicular block? - Left (up in I, down in aVF); lead II negative = -30 to -90°
- Rs in lead I, rS in lead III
- LAFB = bifascicular block (RBBB + LAFB)
What findings suggest LVH? - Increased voltage in aVL (> 11 mm) - LVH can be diagnosed in RBBB
- aVF (~19 mm) just misses the aVF ≥ 20 mm criterion
What do the precordial leads show? - Counterclockwise (early) transition due to the RBBB
ECG 36
[Insert image - Garcia ECG 13-36]
The QRS is wide (≥ 0.12 s). Is there a LBBB, RBBB, or IVCD? - RBBB - slurred S waves in I and V6, rsR' in V1
What quadrant does the electrical axis lie in? Is there a fascicular block? - Left (up in I, down in aVF); lead II negative
- R in lead I, rS in lead III
- LAFB = bifascicular block (RBBB + LAFB)
How does this ECG differ from ECG 35? - Same interpretation, but tachycardic
- R wave progression is normal here (it was abnormal in ECG 35)
ECG 37
[Insert image - Garcia ECG 13-37]
- Normal sinus rhythm, ~75 bpm
The QRS is wide (≥ 0.12 s). Is there a LBBB, RBBB, or IVCD? - V1: qR' with an increased R:S ratio = RBBB
- Slurred S in lead I but not in V6
Why is there no slurred S in V6, and why do V2-V6 look alike? - Incorrect lead placement - the precordial electrodes were bunched tightly together
- Properly placed, V6 should show a slurred S
What quadrant does the electrical axis lie in? Is there a fascicular block? - Right (down in I, up in aVF) - ask "Is this LPH?"
- No - P-pulmonale in lead II (RAE) is an exclusion criterion
ECG 38
[Insert image - Garcia ECG 13-38]
- Sinus rhythm with first-degree AV block
The QRS is wide (≥ 0.12 s). Is there a LBBB, RBBB, or IVCD? - RBBB - slurred S waves in I and V6, RR' complex in V1
What quadrant does the electrical axis lie in? Is there a fascicular block? - Right (down in I, up in aVF)
- S in lead I, qS in lead III, no RAE or RVH
- LPFB = bifascicular block (RBBB + LPFB)
Why is RBBB-LPH more common than isolated LPH? - Damage extensive enough to block the fanned-out posterior fascicle usually blocks another fascicle too
- Most common cause: CAD / ischemia
Is RBBB-LPH more or less stable than RBBB-LAH? - Less stable - only the thin anterior fascicle remains, and any small additional insult blocks it
- High risk of complete heart block, especially in AMI
ECG 39
[Insert image - Garcia ECG 13-39]
The QRS is wide (≥ 0.12 s). Is there a LBBB, RBBB, or IVCD? - RBBB - slurred S waves in I and V6
- rsR' in V1 - the initial r is minuscule but present
What quadrant does the electrical axis lie in? Is there a fascicular block? - Right (down in I, up in aVF)
- S in lead I, qS in lead III, no RAE or RVH
- LPFB = bifascicular block (RBBB + LPFB)
Chapter review: true or false? - You only need an RSR' in V1 to diagnose RBBB - False
- Rabbit ears always begin with an R wave in V1 - False (qR')
- LVH can be diagnosed in RBBB but not LBBB - True
- LBBB can have notching in V5-V6 - True
- In LPH the axis is in the extreme right quadrant - False
- RBBB-LPH is stable when present acutely - False
