Normal exercise electrocardiogram: When heart rate increases during exercise, certain predictable

changes occur in normal ECG. The P-R, QRS and QT intervals shorten, the P wave becomes taller and atrial depolarization wave (Ta wave) becomes prominent causing depression of PR segment. This results in depression of J point for a short period of 0.04 sec. The normal ST segment with exercise is upsloping and slightly convex in form and returns to baseline within 0.04 to 0.06 sec. after J point.

2. Abnormal or positive test (Fig. 11.37): The test is said to be positive for provocable ischaemia when there is depression of J point >1 mm with horizontal ST segment > 1 mm persisting for 0.08 sec (two small squares) from the J point in three successive beats.

End points for termination of stress tests. Exercise tests are terminated when the patient develops symptoms and signs of myocardial ischaemia as given in the Table 11.14.

Table 11.14: Indications for termination of the stress test I. Symptoms and Signs III. Abnormal ECG

• Anginal pain • Abnormal ST segment

• Dyspnoea depression (> 1 mm) or

• Dizziness/syncope elevation (> 1 mm) in non-q wave

• Unsteady gait leads

• Hypotension in presence of pain or abnormal ECG.

II. Arrhythmias e.g. brady- IV. Blood pressure abnormalities arrhythmias and • Systolic BP>250 mmHg tachyarrhythmias e.g. • Hypotension

multiform VPCs or VT V. Heart rate e.g.

• Decreasing heart rate.

Pitfalls

The results of an exercise test are inconclusive due to false negative and false positive results. Exercise testing is an unreliable screening method because in low-risk population (e.g. asymptomatic middle aged women) an abnormal response is more likely to represent a false positive than a true positive test. Nevertheless, certain findings on exercise testing are predictive of severe underlying disease called high risk change (see the Box 11.17).

Box 11.17: HIGHRISKFINDINGONSTRESS ECG

• Low threshold of ischaemia, e.g. ischaemic changes appear within stage 1 or 2 of Bruce protocol.

• Fall in BP on exercise

• Widespread, marked or prolonged ischaemic ECG changes

• Exercise induced arrhythmias.

Table 11.13: Indications and contraindications of stress (exercise) testing

Indications Contraindications

• To confirm the diagnosis of • Unstable angina with recent

angina chest pain.

• To evaluate stable angina and • Advanced AV blocks post-myocardial angina.

• To assess prognosis following • Uncontrolled hypertension myocardial infarction.

• To test effectiveness of • Severe congestive heart failure coronary revascularisation e.g.

coronary angioplasty and bypass surgery

• To diagnose and evaluate the • Left main coronary artery treatment of exercise induced disease.

arrhythmias

• Severe aortic stenosis

• Hypertrophic cardiomyopathy

• Acute associated disease e.g.

systemic illness, pulmonary or renal insufficiency, diabetes or thyrotoxicosis

• Ventricular aneurysm.

The Cardiovascular System (CVS)

Continuous ambulatory electrocardiographic recording (Holter monitoring)

Continuous ambulatory ECG recording (Holter monitoring) is a method of recording one or more leads of ECG for extended period of time (24 hr Holter monitoring) by attaching a small portable solid state tape recorder to the patient (Fig. 11.38). This technique is

useful because ECG is recorded when patient is up and about performing normal activities. It is especially useful for detecting transient episodes of arrhythmias or ischaemia which are likely to be missed on 12-leads routine ECG recording (Fig. 11.39).

Fig. 11.37: Positive stress test (Leads V₃–V₆ depicted). Resting ECG is normal. The ECG during exercise showed depression of J-point and ST segments > 2 mm staying for > 80 msec (25 mall squares) which reverses during the recovery period

Fig. 11.38: Holter monitoring.

Placement of electrodes on the body surface for continuous recording of one or two leads of ECG over a period of hours (24 hr) or days

Figs 11.39A and B: Holter’s monitoring. A. From a patient with Stokes-Adams attacks B. From another symptomatic patient of syncope

A variety of hand-held or implantable patient—

activated devices are available to record the ECG during symptomatic episodes (called event-recorders). These are suitable for investigating those patients who have infrequent but potentially serious symptoms. Many of these devices also have the facility to transmit ECG recording to a cardiac centre through the telephone.

Chest X-ray

A postero-anterior (PA) chest X-ray renders most informations regarding the size and shape of the heart, state of pulmonary vasculature and lung fields. Antero-posterior (AP) chest X-ray is not preferred because it magnifies the cardiac shadow by divergence of radiographic beam and may give false impression of cardiomegaly when it does not exist. It is done only in bed-ridden patients.

An estimate of heart size is determined by ‘cardio-thoracic ratio’, which is ratio of the heart size to the maximum transthoracic diameter.

The cardiothoracic ratio >0.5 (> 50%) indicates cardiomegaly.

The normal cardiac shadow/silhouette

In standard PA view of the chest (Fig. 11.40), the heart is interposed between two translucent lungs as a flask-shaped shadow with one third of its area to the right and two-thirds to the left of the midline. The apex is internal to the mid-line.

The right border of normal heart shadow is constituted by two curves from above downwards:

Fig. 11.40: Normal cardiac shadow on chest X-ray (PA view)

(i) The upper curved portion consists of superior vena cava with ascending aorta.

(ii) The lower convexed portion consists of right atrium the lower margin of which lies on the diaphragm.

The left border is constituted from above downwards by;(i) Aortic knuckle produced by arch of the aorta

(ii) Straight line of the pulmonary conus (pulmonary artery)

(iii) Left atrial appendage

(iv) The wide sweep of the left ventricle ending as apex where it rests on the diaphragm.

Indications of chest X-ray

(i) The overpenetrated PA film can visualize the left atrium very well if enlarged and aorta is particularly seen for calcification. Calcification of pericardium as well as of the valves can also be better seen.

(ii) The right lateral view is of value in localizing right ventricular hypertrophy (RVH) when the anteriorly placed right ventricle is seen closer to the sternum than normal.

(iii) For detection of common alterations in diseases of heart such as;

(a) Displacement of the heart in the chest.

• To the opposite side, i.e. pleural effusion, pneumothorax

• Shift to the same side abnormally, i.e.

collapse of the lung, atelectasis, fibrosis and removal of a part or whole lung. In scoliosis, the heart is shifted to the left with convexity towards right.

• In narrow chests and in patients with COPD, the heart lies centrally and seems smaller and tubular.

(b) Abnormal shape and size of the heart.

(i) Cardiomegaly (heart is enlarged and shadow is enlarged)

- Valvular heart disease such as aortic, mitral (mitralised heart), pulmonary and tricuspid valves diseases.

- Hypertension

- Dilated cardiomyopathy, myocarditis - Ventricular aneurysm

(ii) No cardiomegaly but heart shadow is enlarged

- Pericarditis with effusion or cardiac temponade

- Cardiac rupture.

The Cardiovascular System (CVS) - Secondaries in pericardium

- Mediastinal obstruction leading to widening of heart shadow by widening the mediastinum.

Dilatation of individual cardiac chamber can be assessed by the alterations they cause to the cardiac silhouette (heart shadow).

• Left atrial enlargement results in prominence of shadow of left atrial appendage on the left border of heart and a double cardiac shadow to the right of sternum. These changes are characteristically seen in patients with mitral stenosis (read mitral stenosis in bed-side Medicine by Prof. SN Chugh)

• Right atrial enlargement produces prominence and enlargement of right border of the heart towards right lower lung field.

• Left ventricular dilatation causes prominence of left border of heart and enlargement of cardiac shadow (Fig. 11.41).

• Right ventricular dilatation increases heart size and displaces the apex upwards.

Fig. 11.41: Left ventricular enlargement. Note the boot shaped heart

(iv) Detection of abnormalities of shape and size of great vessels and pulmonary vasculature.

(a) Aorta

• Dilatation of ascending aorta occurs due to Marfan’s syndrome, cystic medial necrosis, aneurysm of aorta, syphilis, atherosclerosis and acute dilatation occurs in aortic dissection. Post-stenotic dilatation is seen in severe aortic stenosis,

• Unfolding of aorta (both ascending and descending aorta may be involved) is seen in patients with hypertension and old age.

(b) Prominent superior vena cava shadow: It is seen in the upper part of right border of the heart in patients with;

• Right ventricular failure.

• Superior vena cava obstruction.

(c) Prominent pulmonary artery (conus). The enlargement of pulmonary artery causes prominence of pulmonary conus in patients

• Pulmonary hypertension due to any causewith

• Post-stenotic dilatation in pulmonary stenosis

• Idiopathic dilatation of pulmonary artery.

(d) Prominent pulmonary vasculature. The pulmonary vasculature becomes prominent in raised left atrial pressure producing congestion in the lungs characterized by:

• Prominent hilar shadows

• Kerley’s B lines. These are short horizontal lines extending out to the lung edges or the bases of lung

• Prominence of upper lobe veins

• Interstitial pulmonary shadowing either as diffuse haziness or a bat-wing appearance of acute severe pulmonary oedema (haziness from hilum extending towards periphery).

(e) Pulmonary plethora. The main branches of the pulmonary arteries are dilated and engorged.

This occurs in;

• Left to right shunt (e.g. ASD, VSD, PDA).

This is best seen on fluoroscopy (screening) discussed below.

(f) Pulmonary oligaemia. The pulmonary vasculature is inconspicuous in;

• COPD where there is pruning of peripheral vessels due to compression by the hyperinflated alveoli.

• Fallot’s tetralogy.

Radiographic findings in heart failure

Characteristic radiological findings are observed on chest X-ray in patients with left heart failure. These are mainly due to elevation of pulmonary venous pressure and interstitial oedema. These are:

1. Abnormal distention of upper lobe pulmonary veins.

2. Vascularity of lung fields is increased and pulmonary artery is dilated.

3. Kerley’s ‘B’ lines become evident at costophrenic angles due to interstitial oedema. These lines represent thickened interalveolar septa and dilated lymphatics.

4. More advanced cases show non-homogenous opacification spreading from the hilar regions to periphery (Fig. 11.42).

5. There may be interlobar effusion and hydrothorax.

The abnormal cardiac conditions and their radiological features have discussed in bed side medicine by Prof. SN Chugh.

Fluoroscopy for hilar dance

Hilar dance is a radiological finding seen in congenital heart disease with moderate left to right shunt Pulmonary vascular markings are prominent and pulmonary artery is dilated. Pulmonary arteries show increased pulsations from hilum to periphery which can easily be seen on fluoroscopy of chest. This is due to increased blood flow through pulmonary vessels.

Screening of the heart is primarily of value in visualising the calcification and in detecting a left ventricular aneurysm.

Echocardiography

Echocardiography is ultrasound imaging of heart and great vessels. Ultrasound is reflected at interfaces between blood and solid tissues because velocity of sound is constant in body tissues. These sounds are then gathered and they collectively give the anatomical dimensions of the structure to be studied. Therefore, it is useful in studying the blood flow, the structure of the heart and movements of valves and cardiac muscles. It is done by placing a transducer on the chest which

passes sounds and collects the reflected sounds which are displayed and studied.

Type of studies

Three types of study are performed

1. M-mode echocardiography: A single transducer

In document Clinical Methods in Medicine (Page 192-196)