CONTENTS

• P-wave axis
• Left atrial abnormality (LAA)
• Right atrial abnormality
  • RA enlargement
  • RA strain
• Biatrial abnormality
• Bayes syndrome

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P-wave axis

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normal P-wave axis

• 0-75 degrees.
• P-wave should be upright in I, II, and aVF.
• P-wave should be inverted in aVR.

causes of abnormal P-wave axis

• Various:
  • Ectopic atrial rhythm.
• Right shift (flattened in Lead I;  strongly positive in Leads III and aVF; negative in aVL):
  • Dextrocardia.
  • Vertical heart configuration.
  • Limb lead reversal.
  • Right atrial enlargement.
• Left shift:
  • Horizontal heart configuration.
  • Left atrial enlargement.
  • Some congenital heart diseases (P congenitale).

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left atrial abnormality

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two criteria are most helpful: 

• [1] P-wave duration >120 ms:
  • This might be the most accurate predictor of left atrial dilation (with an odds ratio of 2.5). (20537347, 35333097)
  • Isolated P-wave duration >110 ms without other morphological features of left atrial abnormality (as discussed below) may indicate intra-atrial conduction block without left atrial abnormality.
• [2] V1 with exaggerated negative deflection:
  • ECG findings:
    • Negative deflection duration multiplied by depth is >40 ms*mm (Morris Index).
    • Negative deflection is greater than the positive deflection.
  • These strongly suggest left atrial dilation.
  • Differential diagnosis:
    • Pectus excavatum.
    • Severe right atrial dilation (prominent P-terminal force in V1).
    • V1 is placed too high: 📖

Lead II may provide some confirmatory evidence

• P-mitrale: Double-humped P-wave with a peak-to-peak interval of >30 ms and total duration >120 ms.
  • Causes include:
    • Left atrial hypertrophy, dilation, or acute rise in left atrial pressure.
    • Intraatrial conduction delay.
• Tall P-wave may represent left atrial enlargement in up to 30% of cases (pseudo-P-pulmonale). (O'Keefe 2021)
• ⚠️ Massive limb lead P-waves (>2.5 mm high & >3 mm wide) indicate biatrial abnormality.

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clinical significance of left atrial abnormality 

acute LAA can reflect volume overload

• Acute volume overload may generate exaggerated negative deflection in V1 that resolves following diuresis. (de Luna 2022)
• Comparison with recent ECGs may be helpful.

underlying substrate of LAA

• LAA usually reflects either:
  • (1) Left ventricular failure.
  • (2) Mitral stenosis (with a normal left ventricle).
• LAA contributes 3 points to the Romhilt-Estes score for LVH (left ventricular hypertrophy). In the presence of any additional features of LVH, the patient may likely have LVH. 📖

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right atrial abnormality

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predictors of right atrial enlargement (on echocardiogram or CT scan)

• #1 = Large (>1.5 mm) P-wave in V1 or V2 (specific but insensitive).
  • Tall, Peaked P-waves in V1-V2.
• #2 = R>S in V1, in the absence of RBBB.
• #3 = QRS axis >90 degrees.
• (These findings seem to be part of the constellation of RV hypertrophy: 📖).

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P-pulmonale

ECG findings of a P-pulmonale pattern:

• Primary definition:
  • [1] Tall, peaked P-waves in Lead II (>2.5 mm).
  • [2] Sinus rhythm (not ectopic P-waves).
• The P-wave axis is generally >70 degrees (negative P-wave in aVL).
• Large P-waves sometimes cause diffuse ST depression (due to atrial repolarization).

causes of P-pulmonale pattern:

• [1] Acute pulmonary embolism. This doesn't seem to correlate with actual RA dilation on echocardiography, but it may reflect increased wall tension within the right atrium.
• [2] RVH (right ventricular hypertrophy).
• [3] Vertical heart configuration (usually 2/2 hyperinflation) 📖
  • 🔑 Prominent P-waves in inferior leads.
  • 🔑 Lead-I sign (low voltage in lead I).
  • 🔑 Low voltage (sometimes with shrinkage of QRS voltage in V4->V5->V6).
  • 🔑 Slow R-wave progression in V1-V3.
  • 🔑 S-waves in V6 and Lead I.
  • ⚠️ No unexplained features suggest PE/RVH (e.g., right precordial TWI, RBBB, tall R-V1). 📖
• [4] Hypokalemia. 📖

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biatrial abnormality

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Biatrial abnormality is suggested by a combination of findings that suggest both left and right atrial abnormality.  The following, in particular, may suggest biatrial abnormality: 

• V1 has large, biphasic P-waves:
  • Initial positive component of 1.5 mm.
  • Terminal negative duration*amplitude >40 ms*mm.
• Lead II P-waves are both tall (>2.5 mm) and wide (>120 ms).

Fakeout: Severe right atrial dilation

• Severe right atrial dilation may cause:
  • [1] Prominent, negative P-wave in V1 (prominent P-terminal force in V1).
  • [2] Tall, sharp, and narrow P-wave in the inferior leads (P-pulmonale).
• This may mimic biatrial abnormality, but both abnormalities are due to right atrial dilation.
• Clues to this diagnosis:
  • [1] The P-wave in the inferior leads is tall but not broad.
  • [2] Marked evidence of RVH.
• Example: ECG Wave Maven 304.

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background

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some general concepts behind atrial abnormalities:

• Normally, the RA depolarizes before the LA.
• RA enlargement leads to an overlap of the RA and LA signals in the inferior leads. This produces tall P-waves with a normal P-wave duration.
• LA enlargement causes the duration of the P-wave to increase.

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Bayes syndrome

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Bayes syndrome

• ECG criteria:
  • [1] Prolonged P-wave (>120 ms or >3 boxes).
  • [2] Biphasic (plus –> minus) P-waves in inferior leads (II, III, aVF).
• Clinical criteria: AF or other atrial arrhythmias.

clinical significance

• ECG findings correlate with a high risk of atrial fibrillation (as well as stroke and vascular dementia). Even in the absence of atrial fibrillation, ECG findings may reflect fibrotic atrial cardiomyopathy.
• ECG findings are increasingly common with age:
  • 55 years old: ~0.5% prevalence.
  • 75 years old: ~8% prevalence.
  • 100 years old: ~25% prevalence. (32684442)
• Pathophysiologically, this may correlate with the complete blockade of the Bachmann bundle between the atria, leading to retrograde depolarization of the left atrium from areas near the atrioventricular junction. (32684442)

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questions & discussion

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References