CVS Imaging

         Cardiac MRI with delayed postgadolinium imaging ("viability study") is the most sensitive imaging technique for MI. Echocardiography can detect areas of myocardial wall thinning or abnormal myocardial contraction. Cardiac single photon emission computed tomography (SPECT) can detect areas of nonviable myocardium. However, MRI has greater specificity than echocardiography and far greater spatial resolution and sensitivity than SPECT.

·         Arrhythmogenic right ventricular dysplasia or cardiomyopathy (ARVD/ARVC) is a disease of unknown etiology, characterized by fatty or fibrous infiltration of the myocardium. It is a common cause of sudden death and may be familial. Diagnosis is made through a combination of clinical, imaging, electrocardiographic, and pathologic findings. MRI is a useful test for evaluating right ventricular morphology, composition, and function. Suggestive findings on MRI include dysfunction, dilation, or thinning of the right ventricular wall, aneurysms of the right ventricle, and fatty infiltration of the right ventricular wall. Treatment consists of placement of an implantable cardioverter defibrillator. It is important to realize that the diagnosis of ARVD should not be made on the basis of imaging findings alone.

·         Anomalous origin of the coronary arteries occurs rarely (about 1% of cardiac catheterizations). Sudden death is associated with the left main coronary artery arising from the right sinus (particularly when the artery courses between the aorta and pulmonary artery), the right coronary artery arising from the left sinus, or a single coronary artery. The left main coronary artery may also arise from the pulmonary trunk; this anomaly tends to present earlier, with congestive heart failure or sudden death.

·         AORTIC PATHOLOGIC CONDITIONS:

1.       Aortic aneurysm: dilation of the aorta, but all three levels of the aortic wall remain intact.

2.       Pseudoaneurysm: a contained aortic rupture, with disruption of at least one layer of wall.

3.       Dissection: a tear in the intima, with propagation of this tear along the aortic long axis.

4.       Transection: traumatic aortic injury, with compromise of at least a portion of the aortic wall. Most patients with transection die before reaching a hospital.

·         The Stanford classification categorizes dissections into those involving the ascending aorta regardless of involvement of the descending aorta and those involving the descending aorta only:

Type A: Ascending aorta is involved with or without descending aortic involvement

Type B: Descending aorta only

The DeBakey classification denotes three categories of aortic dissection: singular involvement of the ascending or descending aorta or involvement of both ascending and descending aortas. The mnemonic for this system is BAD:

Type 1: Both ascending and descending

Type 2: Ascending only

Type 3: Descending only

·         Approximately 90% of the time, the false lumen is larger than the true lumen.

·         Any artery dilated by more than 50% of its normal size is called aneurismal.

·         An endoleak is defined as residual blood flow in the "aneurysm sac" (in other words, between the native aortic wall and the wall of the stent-graft). This complication is subcategorized based on the origin of the blood flow to the aneurysm sac. Type II endoleaks are the most common and are related to reversed flow into the aneurysm sac from collateral vessels such as the inferior mesenteric artery or lumbar arteries. Screening for endoleaks is usually performed with CTA or MRA. An appropriate protocol requires precontrast images and postcontrast arterial phase and delayed phase images since endoleaks may only be identified on delayed imaging.

·         The most common variant of aortic arch anatomy is termed a bovine arch, in which there are two vessels that arise from the aorta. The more proximal of these is a common trunk of the innominate artery and left common carotid artery. The more distal vessel is the left subclavian artery. This anatomic variant is of no clinical significance, except when planning aortic surgery.

·         Orthodeoxia is a term used to describe position-dependent oxygen desaturation. Most pulmonary AVMs occur in the lower lobes. Shunting of blood and desaturation are maximum when blood flow to the lung bases is greatest. Patients with large pulmonary AVMs in the lower lobes will have larger shunts and lower oxygen saturation when standing. When lying down, blood is redirected toward the lung apices, and the shunt fraction and desaturation may decrease.

·         Scimitar syndrome is a hypogenetic lung (almost exclusively on the right) that is drained by an anomalous vein. This anomalous vein can drain into many structures including the infradiaphragmatic inferior vena cava (IVC), suprahepatic IVC, portal vein, or right atrium. The chest x-ray will demonstrate a small right lung with a tubular opacity paralleling the right heart border (called the scimitar). Magnetic resonance imaging and CT better demonstrate the course and nature of the abnormal vascular anatomy.

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·         There are two main types of intravascular stents: balloon expandable, made from stainless steel, and self-expandable, made from a special alloy called NITINOL. The first type of stent is paramagnetic and creates strong MRI artifacts that prevent imaging of the underlying vessel. NITINOL stents are made from a diamagnetic material that creates fewer artifacts. Both stainless steel and NITINOL stents cause minimal artifacts in CTA and therefore usually do not obscure the underlying vessel.

·         MEASURING DEGREE OF VESSEL STENOSIS

1.       Most accurate method: compare cross-sectional area of stenotic lesion segment to that of a normal segment of the vessel.

2.       Most commonly used method: compare linear diameter of stenotic lesion segment to that of a normal segment of the vessel.

·         Generally, renal veins have more consistent anatomy than renal arteries. Knowledge of the venous anatomy before laparoscopic surgery is important to prevent vascular injury and bleeding. The left vein is longer than the right vein, which is one reason why the left kidney is preferred for transplantation. The most common left renal vein anatomic variant is a circumaortic renal vein, which occurs in 5-7% of the population. With this anatomic variant, the left renal vein forms a ring around the aorta. The anterior segment of the ring connects with the inferior vena cava (IVC) at the expected level of the left renal vein, and the posterior segment connects with the IVC below the insertion of the anterior segment. A retroaortic left renal vein is less common and occurs in 2-3% of people.

·         Currently, the gold standard for the diagnosis of FMD is still conventional arteriography. The main findings of FMD are subtle intimal changes, resulting in a beaded appearance to affected vessels. The resolution of MRA is not sufficient for diagnosis. CTA, using 16- and 64-channel scanners, shows promise for detecting FMD, but it is not considered reliable enough at this time to accurately diagnose FMD.