The heart

8.1. The heart

8.1.1. Developmental abnormalities

Echocardiography plays a decisive role in the imaging of the vast and widely complex field of congenital heart diseases. Its value is further increased by the fact that this harmless

examination is safe to perform in the primarily involved age group, newborns and infants.

Many of the congenital heart anomalies lead to left-to-right shunts in the form of atrial and ventricular septum defects, or patent ductus arteriosus and pulmonary vein transposition. The shunt leads to a state where the right side of heart and the pulmonary circulation suffers a volume and pressure increase and their signs can be detected on chest radiographs.

One of the fundamental questions of the primary diagnostics and the postoperative control examinations is to assess cardiac chamber and valvular morphology. Their other main concern is to determine the cardiac functional status. It is essential to demonstrate precisely, for the success of reconstructive surgical procedures, which are at many times multi-step

interventions, how the ventricular myocardial volume and functionality are, including the individual (split) functional parameters of the left and right ventricle. These sophisticated requirements can be best investigated with MRI. MRI is also able to quantify the blood volume flow in the great vessels, the shunt volumes between the circularity sides and the function of the cardiac valves. With complementary MRA examination, the accompanying abnormalities of thoracic vessels can also be revealed.

8.1.2. Primary cardiomyopathies

Hypertrophic cardiomyopathy most often involves the inter-ventricular septum of the heart.

The involvement can be asymmetrical, more pronounced on the left side and patients demonstrate an obstruction to the outflow of blood from the left ventricle. With US

examination it is relatively easy to detect the uneven thickening of the subaortic septum and the consequent obstruction. MRI examination, besides the detection of the left ventricular morphological and functional disorders, is able to depict the degenerative processes occurring in the myocardium.

61 Fig.1., 2.: Hypertrophic obstructive cardiomyopathy: Longitudinal and short axis slices of delayed enhancement of contrast material in the heart: pathologic enhancement is visible in

the myocardium in the asymmetrically thickened left ventricular wall, referring to a degenerative-fibrotic process.

In case of dilated cardiomyopathy the enlargement is visible in the ventricles. The wall becomes thinner and the pump function becomes impaired, leading to the decrease of the ejection fraction. Most commonly it is caused by coronary diseases, but metabolic diseases, inflammatory processes and toxic damage can also be a cause. The cardiac morphology and function is well assessable with echocardiography, while MRI can play a role in the

differential diagnostics.

Arrhythmogenic right ventricular cardiomyopathy and non-compact cardiomyopathy can only be diagnosed with MRI examination. It is usually necessary to perform when patient presents with recurring, equivocal arrhythmias. In cases of Tako-Tsubo cardiomyopathy the base of the left ventricle shows a circular hypertrophy, while the apex appears normal. In rare instances the disease can present in a reversed distribution. Echocardiography is considered the primary examination, while MRI is only complementary.

8.1.3. Myocarditis

MRI examination is able to detect the direct signs of edematous-infiltrative changes in the myocardium. Moreover, after contrast administration with a delayed image acquisition, it is able to depict irregular and increased contrast enhancement and differentiate it from ischemic damage, which shows a subendocardial distribution.

8.1.4. Ischemic heart disease

The role of diagnostic imaging of ischemic heart disease is to demonstrate the obstructive and congenital anatomic abnormalities of the coronary system. Moreover, it has to assess

myocardial damage and its consequent functional impairment. Furthermore, it has to inform about the complications of myocardial infarction and assist in the planning of surgical or interventional therapeutic procedures and finally it needs to be able to evaluate the efficacy of these treatments.

The traditional imaging modality of the coronary vessels is cardiac catheterization

(coronarography) and it still has an absolute indication in acute coronary syndrome. During the examination not only the identification of the symptom causing stenosis or occlusion (culprit lesion) can be done, but it is also possible to perform dilatation with a balloon catheter or to restore flow with stent implantation.

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If either of these procedures is carried out within 6 hours of symptom onset, myocardial dearth can be avoided, or it is possible to achieve a radical reduction of its size.

Coronarography of patients with stable angina is only recommended if a high risk of coronary disease persists clinically. CT coronarography can replace cardiac catheterization in low and medium risk patient groups who present with angina-like chest pain. The examination has a very high sensitivity and negative predictive value for coronary disease; therefore it is a sensitive screening tool for patients who present chest pain as a symptom of coronary stenosis. Moreover, it can provide alternative diagnoses for chest pain syndromes. CT examination is not only good in representing the vascular lumen, but it is also capable of sensitively detecting possibly vulnerable plaques showing a special morphologic appearance;

a lipid rich composition. These lesions might remain hidden for coronarography, producing false negative results with regard to an existing significant atherosclerotic involvement.

Fig. 3., 4., 5.: CT coronarography: Normal anatomy, volume rendered image and curved reformatted image Plaque causing stenosis on LAD coronary artery

Myocardial ischemia causes ventricular wall motion abnormalities, which in latent ischemia only appear with provocation. Ischemia induced cardiac hypokinesis and akinesis can be sensitively detected with stress echocardiography or with MRI. Coronary stenosis related angina is caused by the decrease in myocardial perfusion. This can occur in resting states, but can be reliably demonstrated with stress tests. Traditionally, perfusion evaluation is carried out with radionuclide examinations: either 99mTc-sestamibi SPECT scan or even PET examination is able to detect perfusion anomalies. MRI examination, carried out with complementary pharmacological stress examination, can also prove to be sensitive with this regard.

If the diagnosis of coronary disease has already been established, then imaging is used to examine the viability of the myocardium. This is an important influencing factor, because either of the revascularization techniques is only expected to create a significant improvement in the ventricular function if the recanalized myocardial territory shows viability in at least 50% of its wall thickness. Viability can be assessed with isotope examination, CT or MRI.

With MRI, on the delayed contrast enhanced images (5-10 minutes after iv. injection) the non-viable territories or scar tissue show characteristically increased enhancement; and they are easily distinguishable form viable myocardium. The wide-spread use of MRI in cardiac viability assessment is further justified by the fact that it does not necessitate the use of ionizing radiation. Moreover, with only one diagnostic session it still provides the best anatomic and functional analysis, demonstrates the functionality and the state of the myocardium and myocardial viability.

63 Fig.: 6., 7., 8.: MRI: Extended myocardial infarct of the inferior ventricular wall Late phase

contrast enhancement in the thin inferior wall of the ventricle in cross sectional and longitudinal images, MRI

Echocardiography can be used for the detection and the follow-up of complications of acute myocardial infarcts. Its great advantage, compared to other modalities, is that it can be

performed as a bedside examination, at any time and repeated as often as it is necessary. It can sensitively analyze the state, the function and the wall motion abnormalities of the left

ventricle. The papillary muscles and any septum rupture are also detectable with it. Moreover, echocardiography is sensitive for the detection of aneurysms, intramural thrombus or for the appearance of pericardial fluid collections. Chronic and stable patients can normally be controlled with MRI, which in turn provides detailed information.

8.1.5. Valvular diseases

Indirect signs that indicate valvular abnormalities can be identified by traditional chest

radiography examinations. In aortic insufficiency a pronounced expansion of the left ventricle is seen, while the aortic arch appears widened and elongated. In mitral insufficiency both the left atrium and ventricle are enlarged and pulmonary edema is frequently present as a result of left-sided cardiac failure. In mitral stenosis the left ventricle appears smaller while the left atrium and the auricle are both expanded. There is also an elevated pulmonary pressure and congestion. Furthermore, in more advanced cases of mitral stenosis, an increased arterial pressure and the expansion of the right ventricle can be seen. In pulmonary stenosis and in pulmonary insufficiency both the right ventricle and the pulmonary trunk are enlarged.

Echocardiography provides real-time imaging of the valvular structure and its function. It is able to visualize anatomic distortions of the membranous valve structure and related valvular vegetations and it can equally well identify stenotic lesions or septal closure abnormalities.

Doppler examination can precisely measure the acceleration in the blood flow, which in turn can be used to estimate the pressure gradient of the stenosis, or in case of insufficiency, the grade of regurgitation. Echocardiography can be used to reliably measure and to follow-up the dilation of any cardiac chamber. Compared to the radiographic evaluation of left ventricle hypertrophy in aortic stenosis, ultrasonography examination is also superior, since left ventricle enlargement on radiographs can remain unnoticed up until the heart failure is so advanced that the ventricle is already irreversibly damaged.

MRI or CT examinations are not routinely used for the assessment of the valves. However, for other reasons (primarily in congenital heart diseases) these techniques can also be informative about the valvular morphology and function. MRI has the advantage that it is able to measure flow rate, while CT is more sensitive in the identification of valvular calcifications.

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8.1.6. Radiologic aspects of arrhythmias

Cardiomyopathies predispose for arrhythmias, amongst which the most typical is

arrhythmogenic right ventricular cardiomyopathy. MRI has the greatest diagnostic role in this aspect, since it is able to judge the morphologic deviation of the right ventricle and the

structural changes of the myocardium with a remarkable accuracy.

In atrial fibrillation due to the altered hemodynamic states, thrombus formation in the atrium is a frequent complication; it is most prevalent in the left auricle and it threatens with the risk of systemic embolisation. Echocardiography is routinely applied in patients with atrial fibrillation to rule out the cardiac origin of the embolisation. Intra-auricular thrombosis, the most frequent source of cardiac embolisation, is evaluated best with transesophageal echocardiography technique.

Catheter thermoablation is an available procedure to prevent atrial fibrillation. For the planning and the implementation of this intervention it is necessary to know the precise anatomic arrangement of the left ventricle and the pulmonary vein ostia. Both, MRA and CTA examinations can provide the necessary 3D information for these procedures.

8.1.7. Diseases of the Pericardium

Pericardial effusion appears as an opacified, dense mantle about the heart on the chest X-ray image. However, echocardiography is the technique to detect pericardial effusion with in the easiest and most reliable manner. It can already be helpful in the optimal localization of a possible puncture site. If ultrasonography cannot provide unequivocal acquisition in complex inflammatory states or cancerous conditions, then CT or MRI examinations are required. The complications of pericarditis can be subsequent thickening of the pericardium and sclerotic callus formations that all lead up to the development of constrictive functional disorders, which might require surgical interventions. Although echocardiography can depict sclerotic lesions, it is unable to visualize the pericardial surfaces in their full extent. CT scanning is sensitive in the imaging of sclerosis and when it is performed with ECG gated guidance it is even capable of functional analysis. Even with regard to pericardial diseases the most complex characterization is still possible with MRI, although it has a reduced sensitivity for the determination of sclerotic lesions.

8.1.8. Cardiac tumors

The most common primary cardiac tumors are myxomas originating from the endocardium and the valves. They are typically depicted as mobile, intra-cavital masses; their imaging is possible with echocardiography, CT or MRI. The most common tumor originating form the myocardium is – the often multifocal – rhabdomyoma. Secondary tumors of the heart can be metastases from real hematogenous spread; the primary tumors are most often breast-, lung carcinomas or melanoma. Secondary tumors can also result from direct propagation of thoracic, most commonly, primary pulmonary tumors that reach the heart. Echocardiography can raise the suspicion that a tumor is infiltrating the cardiac wall and chamber, however it is not able to completely demonstrate the possible extra-cardiac tumor component and it is not as effective in differentiating the lesion from the normal myocardium.

65 Another fundamental question is to determine how much of the actual intra-cavital pathologic lesion is made up of viable tumor tissue and how much of it is a thrombogenous growth on its surface. This is best assessable with MRI examination. Tumors with extra-cardiac,

mediastinal or pulmonary infiltration might require the use of CT examination in order to determine the full extent of the tumor components.

8.1.9. Injuries

Injuries penetrating the cardiac chamber cause pericardial hematoma – if they do not cause pericardial tamponade – then echocardiography can be used for identification and follow-up.

Blunt force trauma causes myocardial contusion that can appear as a myocardial infarct both clinically and in the lab results. Edema and necrosis involving the myocardium can be demonstrated with MRI.