Diagnostic Testing: Difference between revisions

Echocardiography is based on the use of ultrasound directed at the heart to create images of cardiac anatomy and display them in real time on a digital screen. The transthoracic echocardiography is obtained by placing a transducer in various positions on the anterior chest The processing of the ultrasound waves creates cross-sectional images of the heart and great vessels in a variety of standard planes. In general, echocardiography is a sensitive and non-invasive tool for detecting anatomic abnormalities of the heart and great vessels. [Figure 3]

   

The two-dimensional echocardiographic imaging technique is used to investigate the heart in multiple planes in order to asses the existence of (dys)function and structural abnormalities of cardiac chambers and valves throughout the cardiac cycle. Both the cross sectional and longitudinal views are used to look for the presence of any anatomical or functional abnormalities with most of the structures of the heart. [Figure 4&5]

   

   

In addition, in the cross sectional planes ventricular wall motion and left ventricular wall thickening during systole (an important measure of myocardial viability) can be investigated. The systematically assessment of cross sectional segment can also be used to estimate left ventricular volumes and ejection fraction. [Figure 6]

   

Although the two-dimensional imaging technique gives superior view of the important structures of the heart, the analog echocardiographic display referred to as M-mode, motion-mode, or time-motion mode, is still in use for the high resolution axial and temporal imaging. The analog technique is preferred to measure the size of structures in its axial direction, and its high sampling rate allows for the resolution of complex cardiac motion patterns. [Figure 7]

   

Doppler ultrasound is a technique of combined with the traditional ultrasound technique. The Doppler technique assesses changes in frequency of the reflected ultrasound compared with the transmitted ultrasound. The difference is used to be translated in a picture of the flow velocity. The continuous-wave Doppler mode is used to quantitate the exact velocity of the flow and estimate the pressure gradient when high velocities are suspected. The technique creates a graphic representation of the flow velocity in echotransducers’ beam in a time continuous wave. The technique is hampered by the fact that anatomical structures can make disturb the beam and subsequently the flow velocity measurement. When there is ambiguity about the source of the high velocity, pulsed-wave Doppler could be a more useful tool. This technique is range-gated in order to make it possible to investigate specific areas along the beam (sample volumes).  Another technique widely integrated in echocardiography is the colour Doppler. The colour Doppler technique projects in coloured images informative for the direction of flow, the velocity, and the presence or absence of turbulent flow. The flow velocity colour images are in real-time combined with the two-dimensional structural imaging to investigate blood flow in the heart and great vessels. The colour Doppler image technique is in particular of use in detecting regurgitant blood flows across cardiac valves or to visualise any abnormal communications in the heart. [Figure 8]

   

The non-invasive echocardiography has now largely replaced cardiac catheterization for calculation of the hemodynamics changes caused by valvular disease. Several examples of methods to examine hemodynamics of the heart and valves by echocardiopgraphy are:

Unfortunately, it is impossible to obtain high-quality images or Doppler signals in as many a small percent of patients. Underlying conditions such as obesity, emphysema or chest wall deformities can limit the use of transthoracic echocardiography. A technique to partly cope with these limitations is transoesophageal echocardiography (TEE) [figure 9].  

   

With TEE a smaller ultrasound probe is placed on a gastroscopic device for introduction in the oesophagus behind the heart. Besides overcoming structural problems, in general TEE produces much higher resolution images of posterior cardiac structures. With TEE left atrial thrombi, small mitral valve vegetations, and thoracic aortic dissection can be diagnosed a high degree of accuracy. The downside of the techniques is the invasiveness of the procedure; the introduction of a probe into the oesophagus is very often experienced as rather uncomfortable by patients.

*Myocardial resonance imaging

   

The induced cardiac stress is most widely used to compare the coronary circulation during exercise with the circulation in rest. An imbalance between myocardial oxygen supply and demand due to coronary disease can be revealed as a result of the increased oxygen demand during stress conditions. By this means stress testing can reveal myocardial ischemia during exercise, while no symptoms are present at rest. Furthermore, stress testing can also be used to determine cardiac reserve in patients with valvular and myocardial disease. Deterioration of left ventricular performance during the test suggests a decline in cardiac reserve that could have therapeutic and prognostic implications.