Sunday, September 8, 2013

ECG Blog #75 — LAA vs LAE vs Not ...

The 12-lead ECG shown below in Figure-1 was obtained from a 27-year old man.
  • Does the patient have a large right atrium?
  • Any other abnormality?

Figure-1: ECG obtained from a 27-year old man. Is there RAE (Right Atrial Enlargement)? 

We interpret the ECG shown in Figure-1 as follows:
  • Sinus rhythm (upright P in lead II ) — with slight variation in R-R interval consistent with sinus arrhythmia. Intervals (PR/QRS/QT intervals) are normal. The axis is somewhat “vertical” — although still within normal range (positive in both leads I and aVF, although obviously much closer to aVF). We estimate that axis to be between +75-80 degrees.
  • RAA (Right Atrial Abnormality) — as P waves are tall and peaked in each of the inferior leads. The P wave in lead II is more than half a large box tall (>2.5mm). Otherwise — No evidence of chamber enlargement.
  • QRST Changes: There are small, narrow q waves in multiple leads (seen in leads II,III,aVF; and V3,V4,V5,V6). Transition occurs normally between leads V2-to-V3. There is shallow T wave inversion in lead aVL — but otherwise no acute changes.
IMPRESSION: Sinus arrhythmia. RAA. Small q waves in multiple leads. Otherwise unremarkable ECG for a 27-year old man. We make the following comments:
  • The obvious first question is WHY did this 27-year old man have an ECG done in the first place? We are not told if the patient was otherwise healthy and required to have an ECG as part of a pre-insurance exam or some other screening procedure — vs chief complaint of acute or longterm shortness of breath.
  • Sinus arrhythmia as seen in Figure-1 is a normal variant in a young adult.
  • The ECG presence of “RAA” is not necessarily indication of right atrial “enlargement”. It is not necessarily an abnormal finding in a young adult with a relatively vertical axis (See below).
  • Although QRS voltage initially looks to be “increased” — criteria for LVH (Left Ventricular Hypertrophy) are not satisfied because the patient is 27 years old. As discussed in ECG Blog #73 — QRS amplitude is often increased in younger adults without this necessarily reflecting true chamber enlargement. Thus although sum of deepest S in V1,V2 + tallest R in V5,V6 in Figure-1 clearly exceeds 35mm — this does not qualify as “voltage for LVH” since this patient is less than 35 years of age (See Figure-2 in ECG Blog #73).
  • The shallow, symmetric T wave inversion in lead aVL is not abnormal as an isolated finding. Isolated T wave inversion may be normal in one or more of the following leads: III, aVR, aVL, aVF and lead V1 (See Figure 4 in ECG Blog #9). The isolated T inversion in lead aVL seen here in Figure-1 is especially likely to be a normal finding given that the QRS complex is predominantly negative in this lead (T wave axis often follows close behind QRS axis).
  • Small q waves are seen in multiple leads in Figure-1. Small lateral q waves are commonly seen in one or more lateral leads (leads I,aVL; V4,V5,V6). When no other abnormality is present — these are termed, normal septal q waves. They simply reflect that the ventricular septum is normally activated from left-to-right — such that lateral leads see the initial ventricular depolarization vector as moving away from the left (thereby writing a small, narrow initial deflection in one or more of the lateral leads). While a q wave is not usually seen as far anteriorly as lead V3 (as it is in Figure-1) — this probably reflects the relatively tall R wave that is seen in lead V3 in Figure-1. It is therefore not necessarily abnormal. Finally — normal septal q waves may occasionally be seen in inferior leads in otherwise healthy individuals who manifest a relatively vertical axis. Bottom Line: — The presence of multiple small and narrow q waves is not necessarily an abnormal finding for a 27-year old man with a relatively vertical QRS axis and no acute ST-T wave changes.
Clinical Impression: In the absence of any history or physical exam findings to suggest otherwise — the ECG in Figure-1 may well turn out to be of no particular concern.

ATRIAL ENLARGEMENT: How is it Detected on ECG?
We devote the rest of our discussion to exploring the issue of ECG assessment for atrial enlargement. The point to emphasize is that the ECG is neither sensitive nor specific in assessing for atrial enlargement. If you really need to know about atrial dimensions — Echo is far more accurate. That said — there are times when the ECG may provide important clues which clinically are very helpful.
  • Recognition of LAA (Left Atrial Abnormality) — may support the ECG diagnosis of LVH.
  • This is especially true when underlying bundle branch block is present.
  • Recognition of RAA (Right Atrial Abnormality) in association with other ECG signs — may strongly suggest RVH (and/or pulmonary hypertension). It may also suggest acute pulmonary embolus.
  • ECG signs of multichamber enlargement (at least LVH, LAA, RAA  and possibly also RVH) in a patient with underlying heart disease suggests cardiomyopathy.
ECG Recognition: The 2 leads to use to assess for atrial enlargement are leads II and V1. Normal and abnormal findings for sinus rhythm (NSR), RAA and LAA are summarized for these 2 leads in Figure-2:
  • Note that with NSR (Normal Sinus Rhythm) — the P is upright in lead II and may be upright, negative or biphasic in lead V1.
  • With RAA — the P wave is tall (≥2.5 mm) and pointed in lead II.
  • With LAA — the P is either notched in lead II and/or there is a deep negative component to the P in lead V1.

Figure-2: ECG signs of atrial enlargement. 

Physiologic Rationale: The physiologic rationale for ECG signs of atrial enlargement is based on: i) anatomic location of lead V1 (the V1 electrode lies over the RA = right atrium) — and  ii) relative direction of RA and LA depolarization with respect to the SA node (Figure-3).
  • With NSR (Normal Sinus Rhythm the impulse begins in the SA Node  which lies in the upper part of the right atrium (Panel A in Figure-3). Activation of the RA will therefore be seen as approaching lead V1 — whereas activation of the LA will be seen as moving away from lead V1 (red arrows in Panel B). This explains why in theory — the P wave in lead V1 should normally be biphasic, with an initial positive component (as the RA is depolarized) — followed by a negative component (as the LA is depolarized). In Practice — the P wave in lead V1 may normally be positive, negative or biphasic (See NSR in Figure-2 above).
  • The reason the P wave is normally upright in lead II with sinus rhythm is shown in Panel C of Figure-3. Summation of RA and LA activation is seen as moving toward lead II at +60 degrees (arrows in Panel C).

Figure-3: Physiologic basis for why with NSR (Normal Sinus Rhythm) — the P in V1 may be positive, negative or biphasic (Panel B) — and why the P wave in lead II is upright (Panel C).

ECG Criteria: The Normal P Wave in Leads II, V1
Appreciation of concepts illustrated in Figure-3 facilitates understanding the ECG signs of atrial enlargement shown in Figure-2:
  • With NSR (Normal Sinus Rhythm the P wave in lead V1 may normally be upright, negative or biphasic.
  • The finding of a negative P wave in lead V1 is therefore not abnormal.
  • NOTE: Be aware that minor deviation from correct lead placement may alter P wave appearance in V1. Despite best intentions — precordial lead misplacement is relatively common. For example, positioning leads V1 and V2 too high (by 1 or 2 interspaces) on the chest — may result in prominent P wave negativity, that in lead V1 might falsely suggest LAA (Please see My Comment at the bottom of the page on Dr. Smith's Nov. 4, 2018 ECG Blogfor 3 Clues to quickly recognize malposition of electrode leads V1 and V2).

RAA: ECG Criteria (See Figure-2)
  • RAA (Right Atrial Abnormality is diagnosed by the finding of tall Peaked and Pointed P waves in the Pulmonary leads. Because patients with COPD often have low diaphragms (and therefore an inferior axis) — we think of the inferior leads (II,III,aVF) as the "pulmonary" leads.
  • The P wave should be at least half a large box tall (=2.5mm) — in at least one of the inferior leads to satisfy criteria for RAA.
  • IF the P looks "uncomfortable to sit on"Think RAA! = P Pulmonale.
  • Lead V1 is usually not helpful in the ECG diagnosis of RAA. That said — on occasion you may see relatively pointed P waves (not necessarily half a large box tall) in lead V1 — that strongly suggests RAA.

LAA: ECG Criteria (See Figure-2)
  • LAA (Left Atrial Abnormality is diagnosed by finding an mshaped (notched) and widened P wave (≥0.12 second) in a "mitral" lead (I,II,aVL)  and/or a deep negative component to the P in lead V1 = P Mitrale.
  • The reason the P wave becomes wider with LAA is that the left atrium is activated after the right atrium (since the SA Node is in the RA). It is addition of this LA component to the P wave that produces the notch/extra ‘hump’ to form the “M” in lead II.
  • The best ECG sign of LAA is the finding of a deep, negative component to the P in lead V1 — that is at least 1 little box deep or wide.
  • We generally undercall  LAA  because of the poor  specificity  the ECG has for atrial enlargement.

Terminology:  Enlargement vs Abnormality?
Many clinicians use LAA/RAA — and RAE/LAE interchangeably. We prefer the terms, “LAA” and “RAA” (where the A stands for Abnormality) in acknowledgement that an abnormal-looking P wave on ECG does not always mean true atrial chamber “Enlargement”. It simply means a different-than-usual P wave appearance.
  • Other reasons for abnormal P waves include body habitus (tall, peaked P waves may be seen in slender individuals with a vertical axis); increased atrial pressure (ie, from heart failure) and atrial conduction defects.
  • Clinical context will usually suggest whether RAA/LAA is likely to reflect true atrial “enlargement”  or something else. IF we know true atrial chamber enlargement is likely (because of marked LVH or RVH on ECG in a patient with underlying heart disease) — then we may switch to the LA“E or RA“E” designation. Otherwise — we generally prefer to use the terms LA“A or RA“A”.
  • NOTE-1: The atrial don’t “hypertrophy” in that their walls don’t thicken. Instead — the atria enlarge (dilate).
  • NOTE-2: Some of the most abnormal looking P waves (with notching in multiple leads) is seen when there are intra-atrial conduction defects. We suspect this (rather than atrial enlargement) whenever notching and unusual P wave morphology is present in multiple leads ...
CAVEAT (Beyond-the-Core): In keeping with the clinical reality that ECG is neither sensitive nor specific for true atrial chamber enlargement — a phenomenon that I have observed on occasion is that increased atrial pressure (as is commonly seen with acute heart failure) may transiently result in increased P wave amplitude that simulates RAA and/or LAA — but which then resolves within 1-2 days after the patient is treated.

Bottom Line:  Returning to the original case presented of the 27-year old man whose ECG was shown in Figure-1 — the chances are better than not that the tall, peaked and pointed P waves seen in the inferior leads do not represent true atrial chamber enlargement. We say this because of: i) the patient’s age; ii) the relatively vertical QRS axis; andiii) the lack of other abnormality on the tracing. That said — knowledge of the clinical history and physical exam findings (heart murmur?) would be needed to better assess this.
  • Preferential use of the term “RAA” instead of “RAE” — allows us to acknowledge funny-looking P wave on ECG without need to necessarily attribute this to any cardiac pathology in this 27-year old man who might end up having a normal heart.

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