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Special Investigations In Cardiology: Radiology And Electrocardiography (ECG)
We do not just stop at Inspection, palpation, percussion and Auscultation. We still need to carry out more investigations such as radiograhy and electrocardiography to ascertain our diagnosis.
NOTE: The slideshow below this hub indicates the previous episode of this cardiology series and the next, so if you have been following this series, just click on next on the slide below, if you want to go back, click on previous.
The size and shape of the heart can be assessed from chest radiographs. Postero-anterior views, lateral views and oblique views are used to assess abnormalities of the different chambers. Normally, the cardio-thoracic ratio is less than 50%. Enlargement of different chambers gives characteristic configuration in the x-ray. The contraction of the chambers can be seen by fluoroscopy.
Pulsation of the aorta and pulmonary artery can be observed. Pulmonary congestion, pulmonary oligemia and pulmonary edema can be diagnosed. Serially taken chest radiographs also help in assessing the progress of cardiac disease.
Placement of Leads
Specific waves of the ECG
The electrical changes that take place in the heart during different phases of the cardiac cycle are recorded in the electrocardiogram (ECG). The standard 12 lead ECG consists of three standard bipolar limb leads (L1, L2 and L3), three augmented unipolar leads (aVR, aVL and aVF) and six precordial unipolar leads (V1-V6). When required, further additional leads such as right sided chest leads, high anterior chest leads or left posterior chest leads are also taken. Normal ECG shows the P-wave which is caused by electrical activation of the atria, QRS which represents ventricular depolarisation and T-wave which is caused by ventricular repolarisation. The amplitude of these waves, their configuration, their duration and the time interval between various deflections (P-R, QRS and QT, P-P and R-R intervals) are all studied to derive diagnostic information.
The following are the clinical applications of electrocardiography:
- Determining the heart rate and rhythm;
- to detecting atrial or ventricular enlargement;
- diagnosis of all arrhythmias and disorders of impulse conduction;
- detection, localization and semi-quantification of myocardial ischemia (reversible and irreversible);
- diagnosis of myocardial diseases (myocarditis or cardiomyopathy);
- diagnosis of pericardial diseases (pericarditis, effusion);
- monitor toxicity of drugs like digoxin;
- diagnosis of the cardiac involvement in metabolic diseases like myxedema, thyrotoxicosis;
- determining the cardiac effects of electrolyte disturbances, especially hyper- and hypokalemia; and
- detecting live multiple pregnancy.
The ECG has been employed in several varied clinical situations so that its recording is a routine investigation to look for evidence of heart diseases.
The following modifications have been made over the conventional ECG,
- Stress tests: Master's test and treadmill test, which serve to bring out latent ischemic heart disease.
- Continuous ECG recording to detail paroxysmal arrhythmias. Holter monitoring is the recording of the ECG continuously on tapes which can be analysed in a computer in ambulant subjects.
- His bundle electrography: Electrical activity of the bundle of His may be recorded by an electrode catheter placed near the tricuspid valve under fluoroscopy. This technique known as His Bundle electrocardiography permits division of the P-R interval into two sub-intervals, namely, the A-H interval (an approximation of A-V nodal conduction time) and H-V interval (representing conduction time within the His Purkinje system). Thus, more precise localization of the iste of atrio-ventricular block and distinction between supraventricular and ventricular beats become possible.
© 2013 Funom Theophilus Makama