Cardiovascular Tests And Procedures

Front 1

Tests for Assessing Cardiac Anatomy and Function

Back 1

Application
Tests

Left ventricular function
Echocardiography

Multiple-gated acquisition (MUGA) radionuclide imaging

Gated MRI

Contrast ventriculography

Coronary artery disease diagnosis and prognosis
Exercise or pharmacologic stress testing with ECG, myocardial perfusion imaging, or echocardiography

Magnetic resonance angiography

Coronary angiography

Intravascular ultrasonography

Myocardial viability
Resting single-photon emission computed tomography (SPECT) myocardial perfusion imaging

Stress testing (using low-dose dobutamineSome Trade Names
DOBUTREX
Drug Information
) with echocardiography

Positron emission tomography (PET)

Front 2

Cardiac Catheterization

Back 2

Cardiac catheterization is the passage of a catheter through peripheral arteries or veins into cardiac chambers and coronary arteries. Cardiac catheterization can be used to perform various tests, including angiography, intravascular ultrasonography, measurement of cardiac output (CO), endomyocardial biopsy, and measurements of myocardial metabolism. These tests define coronary artery anatomy, cardiac anatomy, and cardiac function to establish diagnoses and help select treatment. Cardiac catheterization is also the basis for several therapeutic interventions.

Procedure

Patients must be npo for 4 to 6 h before cardiac catheterization. Most patients do not require overnight hospitalization.

Left heart catheterization is most commonly used to assess coronary artery anatomy; it is also useful for assessing aortic BP and systemic vascular resistance, aortic and mitral valve function, and left ventricular (LV) pressure and function. The procedure is done by percutaneous femoral, radial, or brachial artery puncture, and a catheter is passed into the coronary artery ostia or across the aortic valve into the LV. Catheterization of the left atrium (LA) and LV is occasionally done using transseptal perforation during right heart catheterization.

Right heart catheterization is most commonly used to assess right atrial (RA), right ventricular (RV), and pulmonary artery pressure and pulmonary artery occlusion pressure (PAOP)—see Fig. 1: Cardiovascular Tests and Procedures: Diagram of the cardiac cycle, showing pressure curves of the cardiac chambers, heart sounds, jugular pulse wave, and the ECG.; see Approach to the Critically Ill Patient: Pulmonary artery occlusion pressure (PAOP); PAOP approximates LA and, LV end-diastolic pressure. In seriously ill patients, PAOP helps assess volume status and, with simultaneous measurements of CO, can help guide therapy. Right heart catheterization is also useful for assessing pulmonary vascular resistance, tricuspid or pulmonic valve function, and RV pressure; RV pressure may help in the diagnosis of cardiomyopathy, constrictive pericarditis, and cardiac tamponade when noninvasive testing is nondiagnostic. The procedure is done by femoral, subclavian, internal jugular, or antecubital vein puncture; a catheter is passed into the RA, through the tricuspid valve, into the RV, and across the pulmonary valve into the pulmonary artery (see Approach to the Critically Ill Patient: Procedure). Selective catheterization of the coronary sinus can also be done.

Front 3

Coronary Artery Bypass Grafting (CABG)

Back 3

Coronary artery bypass grafting (see also Coronary Artery Disease: Coronary artery bypass graft (CABG) surgery) involves bypassing native coronary arteries with high-grade stenosis or occlusion not amenable to angioplasty with stenting. Indications are changing as percutaneous interventions (see Cardiovascular Tests and Procedures: Percutaneous Coronary Interventions (PCI)) are being increasingly used.

The procedure involves thoracotomy via a midline sternotomy. A heart-lung machine is usually used to establish cardiopulmonary bypass, although new techniques avoid it by directly revascularizing the beating heart. The left internal mammary artery is typically used as a pedicled graft to the left anterior descending coronary artery. Other grafts consist of segments of saphenous vein removed from the leg. Occasionally, the right internal mammary artery or radial artery from the nondominant arm can be used.

Common complications include bleeding, infection, and atrial fibrillation but can involve any system (eg, pulmonary, renal, brain, GI). Typically, hospital stays are 4 to 5 days but may be prolonged by complications.

Front 4

Echocardiography

Back 4

Echocardiography uses ultrasound waves to produce an image of the heart and great vessels. It helps assess heart wall thickness (eg, in hypertrophy or atrophy) and motion and provides information about ischemia and infarction. It can be used to assess diastolic filling patterns of the left ventricle, which can help in the diagnosis of left ventricular hypertrophy, hypertrophic or restrictive cardiomyopathy, severe heart failure, constrictive pericarditis, and severe aortic regurgitation.

In transthoracic echocardiography (TTE), a transducer is placed along the left or right sternal border, at the cardiac apex, at the suprasternal notch (to visualize the aortic valve, left ventricular outflow tract, and descending aorta), or over the subcostal region. In transesophageal echocardiography (TEE), a transducer on the tip of an endoscope visualizes the heart via the esophagus.

TTE, the most common technique, provides 2-dimensional tomographic images of most major cardiac structures. TEE is used to assess posterior cardiac structures (eg, left atrium, left atrial appendage, interatrial septum) because they are closer to the esophagus than to the anterior chest wall. TEE can also produce images of the ascending aorta, which arises behind the 3rd costal cartilage; of structures < 3 mm (eg, thrombi, vegetations); and of prosthetic valves.

Two-dimensional (cross-sectional) echocardiography is most commonly used; contrast and spectral Doppler echocardiography provide additional information.

Contrast echocardiography is 2-dimensional TTE done while agitated saline is rapidly injected into the cardiac circulation. Agitated saline develops microbubbles, which produce a cloud of echoes in the right cardiac chambers and which, if a septal defect is present, appear on the left side of the heart. Usually, the microbubbles do not traverse the pulmonary capillary bed; however, one agent, sonicated albumin microbubbles, can do so and can enter left heart structures after IV injection.

Spectral Doppler echocardiography can record velocity, direction, and type of blood flow. This technique is useful for detecting abnormal blood flow (eg, due to regurgitant lesions) or velocity (eg, due to stenotic lesions). Spectral Doppler echocardiography does not provide spatial information about the size or shape of the heart or its structures.

Color Doppler echocardiography combines 2-dimensional and spectral Doppler echocardiography to provide information about the size and shape of the heart and its structures as well as the velocity of and direction of blood flow around the valves and outflow tracts. Color is used to code blood flow information; by convention, red is toward and blue away from the transducer.

Stress echocardiography is TTE done during and after exercise or pharmacologic stress. Stress echocardiography shows regional wall motion abnormalities that result from an imbalance in blood flow in epicardial blood vessels during stress. Computer programs can provide side-by-side assessment of ventricular contraction during systole and diastole at rest and under stress. Exercise and pharmacologic protocols are the same as those used in radionuclide stress testing. Stress echocardiography and radionuclide stress testing detect ischemia about equally well. The choice between tests is often based on availability, the provider's experience, and cost.

Front 5

Electrocardiography (ECG)

Back 5

The standard ECG provides 12 different vector views of the heart's electrical activity as reflected by electrical potential differences between positive and negative electrodes placed on the limbs and chest wall. Six of these views are vertical (using frontal leads I, II, and III and limb leads aVR, aVL, and aVF), and 6 are horizontal (using precordial leads V1, V2, V3, V4, V5, and V6). The 12-lead ECG is crucial for establishing many cardiac diagnoses, especially arrhythmias and myocardial ischemia (see Table 4: Cardiovascular Tests and Procedures: Interpretation of Abnormal ECGs). It can also identify atrial enlargement, ventricular hypertrophy (see Table 5: Cardiovascular Tests and Procedures: Criteria for ECG Diagnosis of Left Ventricular Hypertrophy), and conditions that predispose to syncope or sudden death (eg, Wolff-Parkinson-White syndrome, long QT syndrome, Brugada syndrome).

Front 6

Electrophysiologic Studies (EPS)

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In electrophysiologic studies, recording and stimulating electrodes are inserted via right- or left-sided cardiac catheterization into all 4 cardiac chambers. Atria are paced from the right or left atrium, ventricles are paced from the right ventricular apex or right ventricular out-flow tract, and cardiac conduction is recorded. Programmed stimulation techniques may be used to trigger and terminate a reentrant arrhythmia.

Electrophysiologic studies are indicated primarily for evaluation and treatment of arrhythmias that are difficult to capture, serious, or sustained. These studies may be used to make a primary diagnosis, to evaluate the efficacy of antiarrhythmic drugs, or to map arrhythmia foci before radiofrequency catheter ablation (see Arrhythmias and Conduction Disorders: Radiofrequency (RF) ablation); various mapping techniques are available.

Front 7

Imaging Tests

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Standard imaging tests include chest x-ray, CT, and MRI. Standard CT and MRI have limited application because the heart constantly beats, but faster CT and MR techniques can provide useful cardiac images.

Chest x-rays: Chest x-rays are often useful as a starting point in a cardiac diagnosis. Posteroanterior and lateral views provide a gross view of atrial and ventricular size and shape and pulmonary vasculature, but additional tests are almost always required for precise characterization of cardiac structure and function.

CT: Spiral (helical) CT may be used to evaluate pericarditis, congenital cardiac disorders (especially abnormal arteriovenous connections), disorders of the great vessels (eg, aortic aneurysm, aortic dissection), cardiac tumors, acute pulmonary embolism, chronic pulmonary thromboembolic disease, and arrhythmogenic right ventricular dysplasia. However, CT requires a radiopaque dye, which may limit its use in patients with renal impairment.

Electron beam CT, formerly called ultrafast CT or cine CT, is used primarily to detect and quantify coronary artery calcification, an early sign of atherosclerosis.

MRI: Standard MRI is useful for evaluating areas around the heart, particularly the mediastinum and great vessels (eg, for studying aneurysms, dissections, and stenoses). With ECG-gated data acquisition, image resolution can approach that of CT or echocardiography, clearly delineating myocardial wall thickness and motion, chamber volumes, intraluminal masses or clot, and valve planes. Sequential MRI after injecting a paramagnetic contrast agent (gadolinium-diethylenetriamine pentaacetic acid [Gd-DTPA]) produces higher resolution of myocardial perfusion patterns than does radionuclide imaging. Blood flow velocities in cardiac chambers can be measured. MRI can assess tissue viability by assessing the contractile response to inotropic stimulation with dobutamineSome Trade Names
DOBUTREX
Drug Information
or by using a contrast agent (eg, Gd-DTPA, which is excluded from cells with intact membranes).

Magnetic resonance angiography (MRA) is used to assess blood volumes of interest (eg, blood vessels in the chest or abdomen); all blood flow can be assessed simultaneously. MRA can be used to detect aneurysms, stenosis, or occlusions in the carotid, coronary, renal, or peripheral arteries. Use of this technique to detect deep venous thrombosis is being studied.

PET: Positron emission tomography (PET) can demonstrate myocardial perfusion and metabolism.

Perfusion agents include carbon-11 (11C) CO2, oxygen-15 (15O) water, nitrogen-13 (13N) ammonia, and rubidium-82 (82Rb). Only 82Rb does not require an on-site cyclotron.

Metabolic agents include fluorine-18 (18F)-labeled deoxyglucose (FDG) and 11C acetate. FDG detects the enhancement of glucose metabolism under ischemic conditions, and can thus distinguish ischemic but still viable myocardium from scar tissue. Sensitivity is greater than with myocardial perfusion imaging, possibly making FDG imaging useful for selecting patients for revascularization and for avoiding such procedures when only scar tissue is present. This use may justify the greater expense of PET. Half-life of 18F is long enough (110 min) that FDG can often be produced off-site. Techniques that enable FDG imaging to be used with conventional SPECT cameras may make this type of imaging widely available.

Uptake of 11C acetate appears to reflect overall O2 metabolism by myocytes. Uptake does not depend on such potentially variable factors as blood glucose levels, which can affect FDG distribution. 11C acetate imaging may better predict postintervention recovery of myocardial function than FDG imaging. However, because of a 20-min half-life, 11C must be produced by an on-site cyclotron.

Front 8

Percutaneous Coronary Interventions (PCI)

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Percutaneous coronary interventions (PCI) include percutaneous transluminal coronary angioplasty (PTCA) with or without stenting. Primary indications are treatment of angina pectoris (stable or unstable), myocardial ischemia, and acute MI (particularly in patients with developing or established cardiogenic shock). Elective PCI may be appropriate for post-MI patients who have recurrent or inducible angina before hospital discharge and for patients who have angina and remain symptomatic despite medical treatment. Percutaneous transluminal angioplasty (PTA) is used to treat peripheral arterial disease (see Peripheral Arterial Disorders: Percutaneous intervention).

PTCA is done via percutaneous femoral, radial, or brachial artery puncture. A guiding catheter is inserted into a large peripheral artery and threaded to the appropriate coronary ostium. A balloon-tipped catheter, guided by fluoroscopy or intravascular ultrasonography, is aligned within the stenosis, then inflated to disrupt the atherosclerotic plaque and dilate the artery. Angiography is repeated after the procedure to document any changes. The procedure is commonly done in 2 or 3 vessels as needed.

Restenosis requiring repeat PTCA or coronary artery bypass grafting (CABG) is the most common complication of PTCA. Restenosis rate is highest (up to 35%) in the first 6 mo after angioplasty but can be reduced by stent insertion and anticoagulation during PTCA.

Stents are most useful for short lesions in large native coronary arteries not previously treated with PTCA, for focal lesions in saphenous vein grafts, and for treatment of abrupt closure during PTCA. The role of stenting in acute MI, ostial or left main disease, chronic total occlusions, and bifurcation lesions is still evolving. Some stents elute drugs (eg, sirolimusSome Trade Names
RAPAMUNE
Drug Information
, paclitaxelSome Trade Names
TAXOL
Drug Information
) that limit neointimal proliferation to reduce the risk of restenosis. In intracoronary brachytherapy, the site of stenosis is exposed to radiation in the form of small pellets embedded in a nylon ribbon temporarily (eg, 30 min) placed in the coronary artery prior to stenting. This appears to decrease the risk of early restenosis, but it is unclear whether later stenosis is slightly increased; trials are ongoing. Radioactive stents have not proven effective at limiting restenosis. Stenting is not risk-free; complications include stent thrombosis, restenosis, bleeding secondary to aggressive adjunctive anticoagulation, side branch occlusion, and stent embolism.

Various anticoagulation regimens are used during and after angioplasty to reduce the incidence of thrombosis at the site of balloon dilation; clopidogrelSome Trade Names
PLAVIX
Drug Information
and glycoprotein IIb/IIIa inhibitors are the standard of care for patients with unstable non-ST-segment elevation MI. ClopidogrelSome Trade Names
PLAVIX
Drug Information
(often in combination with aspirin) is continued for 9 to 12 mo after PCI. Ca channel blockers and nitrates may also reduce risk of coronary spasm.

Contraindications and Complications

Absolute contraindications include lack of cardiac surgical support and significant obstruction of the left main coronary artery without a nonobstructed bypass graft to the left anterior descending or left circumflex arteries. Relative contraindications include coagulopathy, hypercoagulable states, diffusely diseased vessels without focal stenoses, a single diseased vessel providing all perfusion to the myocardium, total occlusion of a coronary artery, and < 50% stenosis.

Significant complications occur in 2 to 3% of patients within 30 days of PCI. Complications besides restenosis are similar to those of coronary angiography, although risk of death, MI, and stroke is greater. Abrupt coronary artery closure secondary to spasm, dissection, or thrombus formation occurs in up to 4%, sometimes causing silent infarction. Treatment consists of drugs (for the disorder causing closure), stents, or, in extreme circumstances, intra-aortic balloon pumps or emergency CABG. Of all angiographic procedures, PCI has the highest risk of contrast nephropathy; this risk can be reduced by preprocedural hydration and use of a nonionic contrast agent, acetylcysteineSome Trade Names
MUCOMYST
Drug Information
, or hemofiltration in patients with preexisting renal insufficiency.

Front 9

Radionuclide Imaging

Back 9

Radionuclide imaging uses a special detector (gamma camera) to create an image following injection of radioactive material. This is performed to evaluate coronary artery disease (CAD), valvular or congenital cardiac disorders, cardiomyopathy, and other cardiac disorders. Radionuclide imaging exposes patients to less radiation than do comparable x-ray studies. However, because the radioactive material is retained in the patient briefly, sophisticated radiation alarms (eg, in airports) may be triggered by the patient for several days following such testing.

Planar techniques, which produce a 2-dimensional image, are rarely used; single-photon emission computed tomography (SPECT), which uses a rotating camera system and tomographic reconstruction to produce a 3-dimensional image, is more common in the US. With multihead SPECT systems, imaging can often be completed in ≤ 10 min. Visual comparison of stress and delayed images can be supplemented by quantitative displays. With SPECT, inferior and posterior abnormalities and small areas of infarction and the vessels responsible for infarction can be identified. The mass of infarcted and viable myocardium can be quantified, helping determine prognosis.

Front 10

Stress Testing

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In stress testing, the heart is monitored by ECG and often imaging studies during an induced episode of increased cardiac demand so that ischemic areas potentially at risk of infarction can be identified. Heart rate is increased to 85% of age-predicted maximum (target heart rate) or until symptoms develop, whichever occurs first.

Stress testing is used for diagnosis of coronary artery disease (CAD) and for risk stratification and monitoring of patients with known CAD. In patients with CAD, a blood supply that is adequate at rest may be inadequate when cardiac demands are increased by exercise or other forms of stress. Stress testing is less invasive and less expensive than cardiac catheterization, and it detects pathophysiologic abnormalities of blood flow; however, it is less accurate for diagnosis in patients with a low pretest likelihood of CAD. It can define the functional significance of abnormalities in coronary artery anatomy identified with coronary angiography during catheterization.

Risks of stress testing include infarction and sudden death, which occur in about 1/5000 patients tested. Stress testing has several contraindications (see Table 7: Cardiovascular Tests and Procedures: Contraindications to Exercise Stress Testing). Patients must be npo for 4 to 6 h before the test.

Front 11

Tilt Table Testing

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Tilt table testing is used to evaluate syncope in younger, apparently healthy patients and, when cardiac and other tests have not provided a diagnosis, in elderly patients. Tilt table testing produces maximal venous pooling, which can trigger vasovagal (neurocardiogenic) syncope and reproduce the symptoms and signs that accompany it (nausea, light-headedness, pallor, hypotension, bradycardia).

After an overnight fast, a patient is placed on a motorized table with a foot board at one end and is held in place by a single strap over the stomach; an IV line is inserted. After the patient remains supine for 15 min, the table is tilted nearly upright to 60 to 80° for 45 min. If vasovagal symptoms develop, vasovagal syncope is confirmed. If they do not occur, a drug (eg, isoproterenolSome Trade Names
ISUPREL
Drug Information
) may be given to induce them. Sensitivity varies from 30 to 80% depending on the protocol used. The false-positive rate is 10 to 15%.

With vasovagal syncope, heart rate and BP usually decrease. Some patients have only a decrease in heart rate (cardioinhibitory); others have only a decrease in BP (vasodepressor). Other responses include a gradual decrease in systolic and diastolic BP with little change in heart rate (dysautonomic pattern), significant increase in heart rate (> 30 beats/min) with little change in BP (postural orthostatic tachycardia syndrome), and report of syncope with no hemodynamic changes (psychogenic syncope).

Relative contraindications include severe aortic or mitral stenosis, hypertrophic cardiomyopathy, and severe coronary artery disease (CAD). In particular, isoproterenolSome Trade Names
ISUPREL
Drug Information
should not be used in patients with hypertrophic cardiomyopathy or severe CAD.