Left atrial enlargement can be identified by changes on the electrocardiagram. The changes in the P wave may be referred to P mitrale due to the association with mitral valve disease.
Situations where left atrial enlargement may occur:
(1) mitral stenosis
(3) arterial hypertension
(4) ischemic heart disease
Criteria from the electrocardiogram for left atrial enlargement (Table I, page 830, Munuswamy et al, 1984):
(1) P terminal force in lead V1 more negative than ( < ) -0.04 mm•s.
(2) duration of the negative of phase of the P wave in lead V1 > 40 ms (0.040 seconds)
(3) depth of the negative phase of the P wave in lead V1 >= 1 mm (0.10 mV)
(4) total P wave duration > 110 ms (0.110 seconds)
(5) notched (indented) P wave in any standard lead (such as II or III) with an interpeak duration > 40 ms (0.040 seconds)
(6) ratio of (total P wave duration in seconds) / (P-R interval in seconds) > 1.6
• P terminal force = (depth of the terminal phase of P wave in mm) * (duration in seconds); the depth of the terminal phase is taken as a negative number. This also termed the Morris index.
• P-R interval is the time from the beginning of the P wave to the beginning of the R wave
• The notching in the P wave is due to separation of left and right atrial peak potentials.
Performance of the criteria when compared to M-mode echocardiography:
Table III, page 831, Munuswamy et al (1984). Hazen et al (1991) showed similar findings for criteria 1, 4 and 5 (Table II, page 825) except for better sensitivity for criterion 4 (62%).
• The diagnosis of left atrial enlargement by electrocardiography is neither sensitive nor specific. Combining 2 or more of the criteria above did not improve performance.
• Many of the electrocardiographic changes associated with left atrial enlargement are related to a prolonged interatrial conduction time (Josephson et al, 1977). A patient with an interatrial conduction defect may give a false positive for left atrial enlargement by ECG, while a patient with left atrial enlargement but without a conduction defect could appear as a false negative.
• Echocardiography and other imaging modalities can be used now if the diagnosis is in question.
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