ECG Blog #269 (77) — What is Poor R Wave Progression? Why Care?

================================

NOTE: I have updated this content on assessment of R Wave Progression from ECG Blog #94 that I wrote in 2014.

• My revised 11-minute ECG Video (MP-77) on assessment of R Wave Progression appears at the BOTTOM of this post!
• CLICK HERE — to download a PDF summary on assessment of R Wave Progression (from ECG-2014-ePub).
• ECG Blog #248 — Reviews the Causes of a Tall R in Lead V1 (including the Audio Pearl in this blog post).
• ECG Blog #205 — Reviews my Systematic Approach to 12-Lead ECG Interpretation (including an Audio Pearl).

===============================

Assessing “R Wave Progression"
Our purpose in using “Q-R-S-T” as a memory aid — is so as not to forget to evaluate the “R” component = “R” Wave Progression in the precordial leads. We schematically illustrate this concept in Figure-1 — in which the heart’s electrical activity is depicted in the Transverse (Horizontal) Plane. The predominant direction of this electrical activity is to the left and posteriorly (as suggested by the large RED arrow in Figure-1). This predominant direction of electrical activity accounts for the change in appearance of the QRS complex in precordial leads V1-thru-V6 as we move across the chest:

• Initially in right-sided lead V1 — the QRS is predominantly negative (an rS complex). This is because lead V1 sees most of the heart’s electrical activity as moving away from the right as the much larger and thicker LV (Left Ventricle) is depolarized.
• Note how the R Wave “progresses” — by getting taller as one moves from leads V1 and V2 toward left-sided leads V5 and V6. In general — R wave amplitude “tops out” by lead V5, and then becomes smaller in lead V6. This is the situation in Figure-1 — although many variations on this pattern of R wave progression are possible.
• We define the point of “Transition” — as the place where the R wave becomes taller than the S wave is deep (highlighted by the GREEN arrow in Figure-1). Normally — transition occurs between leads V2-to-V4. It occurs between lead V3-to-V4 in Figure-1.

Figure-1: Schematic blow-up cross-section of the heart. Precordial lead placement of recording electrodes is suggested by the YELLOW ovals. Note our focus on the predominant direction of the heart’s electrical activity during ventricular depolarization (RED arrow) — and the effect this has on progression of R wave amplitude in the precordial (chest) leads. Initially (ie, in leads V1,V2) — there is a predominant S wave (negative deflection) — because most of the heart’s electrical activity is moving away from these right-sided leads. As one moves across the chest — the R wave becomes taller until the point of transition is reached where the R wave becomes taller than the S wave is deep (GREEN arrow). This occurs between lead V3-to-V4 in this Figure (Transition normally occurs somewhere between lead V2-to-V4).

Septal Depolarization: The final point illustrated in Figure-1 — is the effect septal depolarization may have on the ECG. After the sinus-conducted impulse leaves the AV Node — the very first part of the ventricles to be depolarized is the left side of the interventricular septum. As a result — septal activation normally proceeds from left-to-right (small BLUE arrow in Figure-1).

• Because septal activation normally moves toward right-sided lead V1 — there will often be a small initial r wave (positive deflection) in lead V1, as well as in lead V2 (as is seen in these leads in Figure-1). This small initial r wave may be lost when there is septal infarction.
• At the same time — septal activation normally moves away from left-sided leads V5,V6. As a result — one or more lateral leads (ie, leads I,aVL; V4,V5,V6) will often manifest a small initial q wave (negative deflection) simply as a reflection of normal septal activation. 
• PEARL #1: Lateral q waves are unlikely to indicate prior infarction IF: i) These q waves are small and narrow; and, ii) The clinical scenario and the rest of the ECG appear to be benign.

========================
TEST YOURSELF: Where is the Point of Transition?
Look at the 3 schematic precordial lead sequences in Panels A, B and C of Figure-2. Comment on R wave progression in each of these sequences.

• In each case — Indicate the 2 leads between which Transition occurs.
• What do you think is meant by the term, “late” Transition?

Figure-2: Identify the point of Transition for the 3 precordial lead sequences shown in this Figure. What is meant by the term, "late" Transition? HINT: Transition normally occurs somewhere between lead V2-to-V4.

ANSWER to Figure-2: The R wave “progresses” in each of the 3 sequences shown in this Figure. By this we mean that R wave amplitude is smallest in lead V1 — and then gets taller as one moves to the next precordial leads.

• Normal Transition occurs in Panel B. That is — the R wave becomes taller than the S wave is deep between lead V3-to-V4.
• In Panel A — there is “early” Transition. By this we mean that the R wave becomes taller than the S wave is deep before the normal point of transition. Specifically — Transition in Panel A occurs between V1-to-V2.
• In Panel C — there is "late" Transition. That is, the R wave becomes taller than the S wave is deep after the normal point of transition. Specifically — Transition in Panel C occurs between V4-to-V5.

Putting It Together: Assessing “R Wave Progression"
Insight into the clinical utility of routinely assessing the "R" component in the "Q-R-S-T" parameter is forthcoming from review of Figure-3.

• Panel A in Figure-3 — shows normal R wave progression. Note progressive increase in R wave amplitude across successive precordial leads until the R wave “tops out” in lead V5. Transition is normal in Panel A (occurs between lead V3-to-V4). 
• PEARL #2: Although a QS complex is present in lead V1 — this is unlikely to reflect prior septal infarction because the QS complex is limited to lead V1 (ie, an r wave develops by lead V2 in Panel A). The small and narrow q waves in leads V5,V6 almost certainly represent normal septal q waves. They are unlikely to indicate prior infarction — because of their small size and expected lateral location.
• 
  
• In contrast — anterior infarction is suggested by the precordial lead sequence in Panel B. This is because a QS complex is seen not only in leads V1,V2 — but also in lead V3. FINE Points: We can more specifically qualify location of the infarct in Panel B as being “antero-septal” — because there is loss of the initial r wave in leads V1,V2 (ie, loss of the initial r wave in lead V1 suggests "septal" involvement). 
• Note in Panel B, that despite the QS in V1-thru-V3 — transition is still “normal” (occurs between lead V3-to-V4). Finally — the isolated small and narrow q wave in lead V6 of Panel B is unrelated to the anterior infarction — and almost certainly once again reflects a normal septal q wave.
• 
  
• In contrast, in Panel C — a QS pattern is seen in both lead V1 and V2, but not in lead V3. That is — a small-but-definite initial positive deflection (r wave) is seen in lead V3. The finding of a QS complex in V1,V2 but not in V3 — may or may not be a "normal" finding. Instead, it could indicate: i) A technical lead placement error: ii) Septal infarction; or, iii) A normal variant. Since there may not be any reliable way to distinguish between normal variant vs lead placement error vs prior septal infarction — We simply acknowledge, "QS in V1,V2 — Suggest clinical correlation" in our interpretation. 
• PEARL #3: Statistical odds are far greater (approximately 4-to-1) that either normal variant or lead placement error rather than septal infarction is the reason for a QS complex in V1,V2 but not V3 (as seen in Panel C).

Figure-3: Normal RWP (R Wave Progression) is seen in Panel A. This is in comparison with precordial lead sequences suggestive of anterior MI (Panel B) vs an indeterminate pattern showing a QS complex in leads V1,V2 but not in V3 (Panel C).

KEY Point: The above comments regarding clinical implications of a QS complex in leads V1,V2,V3 hold true only when the QRS complex is narrow. 

• As we have already noted — QRS widening due to LBBB commonly produces QS complexes in anterior leads that are simply the result of the conduction defect (and are not indicative of anterior infarction!).

PEARL #4: There are at least 3 other common reasons for PRWP (Poor R Wave Progression) with a narrow QRS complex that are not the result of prior infarction. These are: i) LVH; ii) LAHB; and, iii) Severe pulmonary disease/COPD.

• Usually at least some r wave will be seen by lead V3 with these other conditions — though not always. 
• Bottom Line: It is sometimes extremely difficult to know with certainty the cause of PRWP when R waves in leads V1,V2,V3 are either very small or absent. Clinical correlation is essential. (See Figure-4 below for a full list of causes of PRWP).

Beyond-the-Core: It is insightful to appreciate the physiologic reason why R wave progression is often “poor” in the presence of these other conditions.

• LVH (Left Ventricular Hypertrophy) — produces an increase in leftward and posterior forces. When marked — these leftward and posterior forces may totally predominate over initial rightward and anterior forces seen in leads V1,V2,V3. The result is reduction in r wave amplitude in anterior leads. At times — there may even be elimination of any r wave at all in leads V1,V2,V3.
• LAHB (Left Anterior HemiBlock) — The bundle of conduction fibers in the LAH (Left Anterior Hemifascicle) lies slightly in front of (anterior to) fibers in the LPH (Left Posterior Hemifascicle). As a result — block in the LAH (as occurs with LAHB) results in an initial posterior direction for electrical activity that is first conducted over the intact LPH. The result may once again be reduction in r wave amplitude in the anterior leads.
• COPD (Chronic Obstructive Pulmonary Disease) — Severe longstanding pulmonary disease leads to an increase in right ventricular forces. In addition — orientation of the heart’s electrical forces in 3 dimensions may be altered by the large emphysematous chest of a patient with chronic COPD. These physiologic changes may result in ECG signs of: i) Poor R wave progression; ii) Persistence of relatively deep precordial S waves in lateral chest leads; and, iii) Reduced R wave amplitude across the chest leads. In the extreme — R waves are markedly reduced in size (and may even be absent) in anterior precordial leads.

==================================

ECG Media Pearl #77 (11:00 minutes Video) — Reviews assessment of R Wave Progression as part of the Q-R-S-T memory aid in the Systematic Approach to 12-lead interpretation (includes clarification of the term, "Poor R Wave Progression vs Transition).

Figure-4: Causes of PRWP (See the Video Pearl just above).

===============================

Related Material of Interest: 

• CLICK HERE — to download a PDF summary on assessment of R Wave Progression (from the ECG-2014-ePub).
• ECG Blog #248 — Reviews the Causes of a Tall R in Lead V1 (including the Audio Pearl in this blog post).
• ECG Blog #205 — Reviews my Systematic Approach to 12-Lead ECG Interpretation (including an Audio Pearl).