Investigations of the Cardiovascular system

Investigations of the Cardiovascular system Electrocardiography Radiology Echocardiography CT imaging MRI Cardiac catheterization Radionuclide imaging

Electrocardiography (ECG) uses: To determine heart rhythm Status of the conducting system To diagnose myocardial ischemia or infarction Chamber enlargement and hypertrophy Effects of drugs & metabolic disorders (electrolyte imbalance, acidosis, etc.)

Principles of the ECG depolarization starts in the sino-atrial node (SA node), spreads through the two atria (sinus rhythm)

Principles of the ECG Transmitted to the ventricles via the AV node, which conducts slowly and regulates the frequency of conduction to the ventricles

Principles of the ECG Normally, the AV node is the only route of impulse transmission to the ventricles. In other areas, the atria are insulated from the vnetricles by the annulus fibrosus

Principles of the ECG The bundle of His passes from the AV node through the annulus fibrosus and divides into the right bundle (RBB) and left bundle (LBB) branches

Principles of the ECG Each bundle branch passes along the corresponding septal surface of the heart & radiates out as the Purkinje system The left bundle divides into the anterior & posterior fascicles

Principles of the ECG Activation of the SA node is not detected on the surface ECG

Principles of the ECG Impulse transmission down the atria triggers atrial contraction & is recorded as the P wave

Principles of the ECG The PR interval represents the delay between the onset of atrial depolarization and the beginning of ventricular depolarization

Principles of the ECG The depolarization wave then spreads to the two ventricles causing ventricular contraction and producing the QRS complex

Principles of the ECG The muscle mass of the ventricles is larger than that of the atria, so the QRS amplitude is greater than that of the P wave.

Principles of the ECG Repolarization starts ~ 300 msec after the end of depolarization The interval from the end of the S wave to the beginning of the repolarization (T) wave is the ST segment, which is normally iso-electric

Principles of the ECG Repolarization of the myocardium produces the T wave The QT interval represents the total duration of ventricular depolarization & repolarization

The ECG Leads Standard leads (Bipolar Leads) Augmented leads Chest leads

Standard leads (Bipolar Leads) Lead I: between left arm & right arm Lead II: between right arm & left leg Lead III: left arm and left leg

Augmented Limb Leads aVL: left arm and central terminal aVR: right arm and central terminal aVF: left foot and neutral central terminal

Chest Leads Six leads: V1-V6 V1 & V2: face the RV V3 & V4: face the septum V5 & V6: face the LV.

Investigations of the Cardiovascular system Electrocardiography Radiology Echocardiography CT imaging MRI Cardiac catheterization Radionuclide imaging

Exercise ECG In patients with angina, the resting ECG may be normal The principle of the test is to stress the heart and observe for ECG changes of ischemia ECG and BP are continuously recorded while the patient is exercising on a bicycle or a treadmill

Ambulatory ECG Monitoring (Holter) Continuous recording of ECG over 24 hours or more Used to detect transient episodes of ischemia or arrhythmia which can rarely be captured during routine, ordinary ECG recording

Imaging The principle of imaging is to reconstruct a three-dimensional structure out of a group of two dimensional images: Silhouette imaging: various structures are overlapped over each other e.g. CXR, angiography, nuclear imaging Tomographic imaging: a group if sections through the structure to be examined e.g. echo, CT, MRI

Radiology of the Heart Chest X-ray: Postero-anterior view (PA view): Size of the heart Shape of the heart Specific chamber enlargement Status of the pulmonary circulation

Radiology of the Heart Cardiac size: Cardio-thoracic ratio (CTR): Normally < 0.5 Enlargement of the heart (cardiomegaly): LV dilatation and dysfunction Pericardial effusion

Radiology of the Heart Left atrial enlargement: Straight heart border (LA appendage) Widening of the carinal angle Double contour of the right heart border

Radiology of the Heart LV enlargement: Enlarged cardiac silhouette Prominent left heart border

Radiology of the Heart RV enlargement: Cardiomegaly Straightening of the left heart border Apex displaced upwards Right atrial enlargement: Prominence of the right border of the heart

Radiology of the Heart Lung fields: Congestion & edema in patients with left heart failure Increased blood flow (prominent arteries and veins) in shunt lesions Oligemic lungs in pulmonary stenosis Pleural effusions in advanced heart failure

Two Dimensional Echocardiography Ultrasound beam passing through the heart generates cross sectional images or “slices” of the heart Various structures can be seen in real time

Two Dimensional Echocardiography indications Assessment of LV function Diagnosis & quantitation of severity of valvular lesions Identification of vegetations Identifying the source of systemic embolism Detection of pericardial effusion

Doppler Echocardiography Sound waves reflected from moving RBCs undergo frequency shift The faster the blood velocity , the greater the frequency shift The direction of moving blood determines whether the reflected signal is positive or negative

Doppler Echocardiography The derived signal can be plotted graphically against time Or, color can be assigned for the reflected signal and superimposed over the 2D image (color flow mapping)

Other non-invasive imaging: CT and MRI Chambers of the heart The great vessels The pericardium Diseases of the aorta The pulmonary arteries Non-invasive imaging of the coronary arteries

Invasive investigation: cardiac catherization A small tube is passed into the heart via a peripheral artery or vein under fluoroscopic guidance Pressure can be measured, flow volumes calculated, radiographic dyes can be infected to outlime the specific chamber or vessel (angiography)