Atrial Hypertrophy

General Characteristics of Hypertrophy

In hypertrophy the heart muscle becomes thicker. Hypertrophy refers to an increase in the size or mass of the heart muscle.

• Increase amplitude of waves
• Axis shift towards greater amount of muscle mass
• Increased duration of waves

Atrial Enlargement or Hypertrophy

• Atrial hypertrophy is best seen in Lead V1 (which is directly over atria)
• P wave in lead V1 will appear diphastic (both positive and negative)

Right Atrial Enlargement (RAE) – Right Atrial Hypertrophy

Right atrial enlargement can result from increased pressure in the pulmonary artery, e.g. after pulmonary embolization

Causes:

• Often a result of severe lung disease

Characteristics

• Right atrial hypertrophy is diagnosed when first part of diphasic P wave is biggest.
• Peaked P waves (P wave height greater than or equal to 2.5 mm) in leads II, III, and aVF
• No change in P wave duration – Width of p wave does not change.

Left Atrial Enlargement (LAE)

AKA: Left atrial hypertrophy, left atrial abnormality.

Leads to delayed activation of left atrium and thus prolonged depolarization and a prolonged P wave.

Background

• Left atrial enlargement (LAE) is due to pressure or volume overload of the left atrium.
• It is often a precursor to atrial fibrillation.

Electrocardiographic Criteria

LAE produces a broad, bifid P wave in lead II (P mitrale) and enlarges the terminal negative portion of the P wave in V1.

Diagnostic criteria are as follows:

In lead II

• Bifid P wave with > 40 ms between the two peaks
• Total P wave duration > 110 ms

In V1

• Biphasic P wave with terminal negative portion > 40 ms duration
• Biphasic P wave with terminal negative portion > 1mm deep

Characteristics

• A notched P wave in Lead II
• Diagnosed when the second part of the diphasic P wave is biggest.
• Increased duration of the P wave; terminal portion of P wave must span atleast one small box (40 msec)
• P wave with a broad (0.04 sec or 1 small square) and deeply negative (>1 mm) terminal part in V1
• P wave duration longer than 0.12 sec in leads I and / or II (Usually lead II)

Causes

In isolation:

• Classically seen with mitral stenosis
• Left atrial enlargement is also known as “P mitrale” because it is associated with mitral valve insufficiency, resulting in back flow of blood from the left ventricle to the left atrium and subsequent increased local pressure.

In association with left ventricular hypertrophy:

• Systemic hypertension
• Aortic stenosis
• Mitral incompetence
• Hypertrophic cardiomyopathy

Broad (>110ms), bifid P wave in lead II (P mitrale) with > 40ms between the peaks

P wave terminal portion > 40 ms duration in V1

Bi-Atrial Enlargement (BAE)

• Diagnosed when RAE and LAE are present
• P wave in lead II > 2.5 mm tall and ≥ 0.12s in duration
• Initial positive component of P wave in V1 > 1.5 mm tall and prominent P-terminal force

Example 1

Biatrial enlargement due to idiopathic cardiomyopathy:

• Biphasic P waves in V1 with a very tall positive deflection (almost 3 mm in height!) and a negative deflection that is both deep (> 1 mm) and wide (> 40 ms).

Example 2

Biatrial enlargement:

• P waves in lead II are tall (> 2.5mm) and wide (> 120 ms).
• P waves in V2 are tall (> 1.5 mm), while the terminal negative portion of V1 is deep (> 1mm) and wide (> 40 ms).

ECG challenge

Two patients provide an opportunity to apply these principles:

A 75-year-old man with pulmonary hypertension has an ECG as part of his yearly examination (Figure 2; click image to enlarge).

Based on the stepwise approach to evaluating an ECG, consider the following:

(1)  Does the ECG indicate a regular heartbeat? Yes, the QRS complexes march out.

(2)  Determine the patient’s heart rate by finding a QRS complex on or near a dark line.

Method A: The number of large boxes between Rs is close to four. Four boxes puts the rate at 75 beats per minute.

Method B: Approximately seven QRS complexes occur in 6 seconds (30 large boxes), which estimates the heart rate at 70 beats per minute (7 × 10 = 70). 

Method C: Dividing 300 by the number of large boxes between QRS complexes (4) yields an estimate of 75 beats per minute.

(3)  A P wave appears before each QRS complex. Is the contour of the P wave the same in all leads? In lead II, the P wave is peaked and has a normal duration. The P wave in V₁ is biphasic, with no increase in the upslope of the first deflection.

(4)  The PR interval spans approximately three small boxes (0.12 seconds), indicating a sinus rhythm. 

(5)  The QRS complex spans fewer than three small boxes, which is normal.

(6)  The ST segments are neutral, so there is no ischemia.

(7)  The T wave is positively deflected in all leads except the aVR. 

(8)  There are no U waves. 

This ECG indicates that the patient is in sinus rhythm and has RAE.

The second patient is a 53-year-old woman who complains of fatigue, dyspnea, and mild chest discomfort. On auscultation, you hear a mid-diastolic low-pitched murmur. The ECG is shown in Figure 3 (click image to enlarge).

 

(1)  Is this ECG regular? Yes, the QRS complexes march out.

(2)  Heart rate:

Method A: The number of large boxes between Rs is close to three. Three boxes would put the rate at 100 beats per minute.

Method B: Approximately 10 QRS complexes occur in 6 seconds (30 large boxes), resulting in an estimated rate of 100 beats per minute (10 × 10 = 100).

Method C: Dividing 300 by the number of large boxes between QRS complexes (3) yields a heart rate of 100 beats per minute.

(3)  There is a P wave for every QRS complex. Is the contour the same? A notched P wave in lead II has a prolonged duration. The P wave in V₁ is biphasic, has an increased down slope in the terminal portion, and spans more than one small box (ie, more than 40 milliseconds in duration).

(4)  The PR interval is approximately three small boxes, which is 0.12 seconds, indicating a sinus rhythm.

(5)  The QRS complex spans fewer than three small boxes, which is normal.

(6)  The ST segments are neutral; there is no ischemia.

(7)  The T wave is positively deflected in all leads except the aVR. 

(8)  There are no U waves. 

This ECG indicates that the patient is in sinus rhythm and has LAE.

Sources: JAAPA