Clinical review

Conditions affecting the left side of the heart

June Edhouse, R K Thakur, Jihad M Khalil. 

Many cardiac and systemic illnesses can affect the left side of the heart. After a careful history and examination, electrocardiography and chest radiography are first line investigations. Electrocardiography can provide supportive evidence for conditions such as aortic stenosis, hypertension, and mitral stenosis. Recognition of the associated electrocardiographic abnormalities is important as misinterpretation may lead to diagnostic error. This article describes the electrocardiographic changes associated with left atrial hypertrophy, left ventricular hypertrophy, valvular disease, and cardiomyopathies.

	Left atrial abnormality

Top Left atrial abnormality Left ventricular hypertrophy Valvular problems The cardiomyopathies

The term left atrial abnormality is used to imply the presence of atrial hypertrophy or dilatation, or both. Left atrial depolarisation contributes to the middle and terminal portions of the P wave. The changes of left atrial hypertrophy are therefore seen in the late portion of the P wave. In addition, left atrial depolarisation may be delayed, which may prolong the duration of the P wave.

View larger version (35K): [in this window] [in a new window]   Biphasic P wave in V1. The large negative deflection indicates left atrial abnormality (enlarged to show detail)

The P wave in lead V1 is often biphasic. Early right atrial forces are directed anteriorly giving rise to an initial positive deflection; these are followed by left atrial forces travelling posteriorly, producing a later negative deflection. A large negative deflection (>1 small square in area) suggests a left atrial abnormality. Prolongation of P wave duration to greater than 0.12 s is often found in association with a left atrial abnormality. Normal P waves may be bifid, the minor notch probably resulting from slight asynchrony between right and left atrial depolarisation. However, a pronounced notch with a peak-to-peak interval of >0.04 s suggests left atrial enlargement.

View larger version (28K): [in this window] [in a new window]   P mitrale in lead II. P mitrale is a P wave that is abnormally notched and wide and is usually most prominent in lead II; it is commonly seen in association with mitral valve disease, particularly mitral stenosis (enlarged to show detail)

Any condition causing left ventricular hypertrophy may produce left atrial enlargement as a secondary phenomenon. Left atrial enlargement can occur in association with systemic hypertension, aortic stenosis, mitral incompetence, and hypertrophic cardiomyopathy.

	Left ventricular hypertrophy

Top Left atrial abnormality Left ventricular hypertrophy Valvular problems The cardiomyopathies

Systemic hypertension is the most common cause of left ventricular hypertrophy, but others include aortic stenosis and co-arctation of the aorta. Many electrocardiographic criteria have been suggested for the diagnosis of left ventricular hypertrophy, but none is universally accepted. Scoring systems based on these criteria have been developed, and although they are highly specific diagnostic tools, poor sensitivity limits their use.

Electrocardiographic findings
The electrocardiographic features of left ventricular hypertrophy are classified as either voltage criteria or non-voltage criteria.

The electrocardiographic diagnosis of left ventricular hypertrophy is difficult in individuals aged under 40. Voltage criteria lack specificity in this group because young people often have high amplitude QRS complexes in the absence of left ventricular disease. Even when high amplitude QRS complexes are seen in association with non-voltage criteriasuch as ST segment and T wave changesa diagnosis cannot be made with confidence. Typical repolarisation changes seen in left ventricular hypertrophy are ST segment depression and T wave inversion. This "strain" pattern is seen in the left precordial leads and is associated with reciprocal ST segment elevation in the right precordial leads.

View larger version (114K): [in this window] [in a new window]   Left ventricular hypertrophy in patient who had presented with chest pain and was given thrombolytic therapy inappropriately because of the ST segment changes in V1 and V2

View larger version (26K): [in this window] [in a new window]   Left ventricular hypertrophy with strain (note dominant R wave and repolarisation abnormality)

      The presence of these ST segment changes can cause diagnostic difficulty in patients complaining of ischaemic-type chest pain; failure to recognise the features of left ventricular hypertrophy can lead to the inappropriate administration of thrombolytic therapy.

View larger version (128K): [in this window] [in a new window]   Left ventricular hypertrophy without voltage criteriain a man who presented with heart failure secondary to severe aortic stenosis (gradient 125 mm Hg). The ST segment changes are typical for left ventricular hypertrophy and there is evidence of left atrial enlargement. If the scoring system is used, these findings suggest left ventricular hypertrophy even though none of the R or S waves meets voltage criteria

Furthermore, in patients known to have left ventricular hypertrophy it can be difficult to diagnose confidently acute ischaemia on the basis of ST segment changes in the left precordial leads. It is an advantage to have old electrocadiograms for comparison. Other non-voltage criteria are common in left ventricular hypertrophy. Left atrial hypertrophy or prolonged atrial depolarisation and left axis deviation are often present; and poor R wave progression is commonly seen.

The electrocardiogram is abnormal in almost 50% of patients with hypertension, with minimal changes in 20% and obvious features of left ventricular hypertrophy in 30%. There is a linear correlation between the electrocardiographic changes and the severity and duration of the hypertension. High amplitude QRS complexes are seen first, followed by the development of non-voltage criteria.

The specificity of the electrocardiographic diagnosis of left ventricular hypertrophy is improved if a scoring system is used.

Scoring system for left ventricular hypertrophy (LVH) suggested if points total 5 Electrocardiographic feature No of points Amplitude (any of the following) 3 Largest R or S wave in limb leads 20 mm S wave in leads V1 or V2 30 mm R wave in leads V5 or V6 30 mm ST-T wave segment changes typical for LVH in the absence of digitalis 3 Left atrial involvement 3 Left axis deviation 2 QRS duration of 0.09 s 1 Delayed ventricular activation time in leads V5 and V6 of 0.05 s 1

	Valvular problems

Top Left atrial abnormality Left ventricular hypertrophy Valvular problems The cardiomyopathies

A normal electrocardiogram virtually rules out the presence of severe aortic stenosis, except in congenital valve disease, where the trace may remain normal despite a substantial degree of stenosis. Left ventricular hypertrophy is seen in about 75% of patients with severe aortic stenosis. Left atrial enlargement may also be seen in the electrocardiogram. Left axis deviation and left bundle branch block may occur.

	The cardiomyopathies

Top Left atrial abnormality Left ventricular hypertrophy Valvular problems The cardiomyopathies

Diseases of the myocardium are classified into three types on the basis of their functional effects: hypertrophic (obstructed), dilated (congestive), or restrictive cardiomyopathy. In cardiomyopathy the myocardium is diffusely affected, and therefore the resulting electrocardiographic abnormalities may be diverse.

Hypertrophic cardiomyopathy
This is characterised by marked myocardial thickening predominantly affecting the interventricular septum and/or the apex of the left ventricle. Electrocardiographic evidence of left ventricular hypertrophy is found in 50% of patients. A characteristic abnormality is the presence of abnormal Q waves in the anterolateral or inferior chest leads, which may mimic the appearance of myocardial infarction. As the left ventricle becomes increasingly less compliant, there is increasing resistance to atrial contraction, and signs of left atrial abnormality are commonly seen. Atrial fibrillation and supraventricular tachycardias are common arrhythmias in patients with hypertrophic cardiomyopathy. Ventricular tachycardias may also occur and are a cause of sudden death in these patients.

View larger version (51K): [in this window] [in a new window]   Abnormal Q waves in patient with hypertrophic cardiomyopathy

   Dilated cardiomyopathy
Many patients with dilated cardiomyopathy have anatomical left ventricular hypertrophy, though the electrocardiographic signs of left ventricular hypertrophy are seen in only a third of patients. In some patients the signs of left ventricular hypertrophy may be masked as diffuse myocardial fibrosis can reduce the voltage of the QRS complexes. If right ventricular hypertrophy is also present the increased rightward forces of depolarisation may cancel out some of the leftward forces, again masking the signs of left ventricular hypertrophy.

Signs of left atrial enlargement are common, and often there is evidence of biatrial enlargement. Abnormal Q waves may be seen, though less commonly than in hypertrophic cardiomyopathy. Abnormal Q waves are most often seen in leads V1 to V4 and may mimic the appearance of a myocardial infarction.

View larger version (95K): [in this window] [in a new window]   Dilated cardiomyopathy (note left ventricular hypertrophy pattern)

Restrictive cardiomyopathy
Restrictive cardiomyopathy is the least common form of cardiomyopathy and is the end result of several different diseases associated with myocardial infiltrationfor example, amyloidosis, sarcoidosis, and haemochromatosis. The most common electrocardiographic abnormality is the presence of low voltage QRS complexes, probably due to myocardial infiltration. Both supraventricular and ventricular arrhythmias are common.

View larger version (83K): [in this window] [in a new window]   Patient with restrictive cardiomyopathy due to amyloidosis (note the low voltage QRS complexes and the right bundle branch block)

	Acknowledgments

The box showing voltage criteria for left ventricular hypertrophy and the box showing the scoring system are adapted from Chou T, Knilans TK. Electrocardiography in clinical practice. 4th ed. Philadelphia, PA: Saunders, 1996.

	Footnotes

R K Thakur is professor of medicine, Thoracic and Cardiovascular Institute, Michigan State University, Lancing, MI, USA, where Jihad M Khalil also worked at the time of submission.

   The ABC of clinical electrocardiography is edited by Francis Morris, consultant in emergency medicine at the Northern General Hospital, Sheffield; June Edhouse, consultant in emergency medicine, Stepping Hill Hospital, Stockport; William J Brady, associate professor, programme director, and vice chair, department of emergency medicine, University of Virginia, Charlottesville, VA, USA; and John Camm, professor of clinical cardiology, St George's Hospital Medical School, London. The series will be published as a book in the summer.