Cardiac Catheterization


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Cardiac Catheterization



Charles J. Davidson, Robert O. Bonow



Indications for Diagnostic Cardiac Catheterization


The decision to recommend cardiac catheterization is based on an appropriate risk-benefit ratio. In general, diagnostic cardiac catheterization is recommended whenever it is clinically important to define the presence or severity of a suspected cardiac lesion that cannot be evaluated adequately by noninvasive techniques. Because the risk for a major complication from cardiac catheterization is less than 0.5% and mortality is less than 0.08%, there are few patients who cannot undergo the procedure safely in an active laboratory. Intracardiac pressure measurements and coronary arteriography are procedures that can be performed best with reproducible accuracy by invasive catheterization. Alternatively, intracardiac pressures can be estimated noninvasively with echocardiography (see Chapter 14). Coronary computed tomography (CT) angiography can also be used for assessment of coronary anatomy (see Chapter 18) and provides adjunctive information on plaque distribution and composition. However, limitations of spatial resolution, heart rate variability, patient cooperation, and radiation dosing limit the ability of CT to replace cardiac catheterization for definition of coronary artery stenosis.


To understand the various indications for diagnostic cardiac catheterization, integration of knowledge from multiple American College of Cardiology/American Heart Association (ACC/AHA) guidelines is necessary.1–9 These guidelines address specific indications for cardiac catheterization related to disease states, including guidelines for the management of patients with valvular heart disease,1 chronic heart failure,2 ST-elevation myocardial infarction (STEMI),3 percutaneous coronary intervention (PCI)4 and coronary artery bypass grafting (CABG),5 unstable angina or non-STEMI,6 and congenital heart disease.7


Cardiac catheterization is indicated in diverse populations. At one extreme, many critically ill and hemodynamically unstable patients are evaluated during acute coronary syndromes, severe heart failure, or cardiogenic shock. At the other end of the spectrum, many procedures are performed in an outpatient setting. Such settings include hospitals with or without cardiac surgical capability and freestanding or mobile laboratories.9


Cardiac catheterization should be considered a diagnostic study used in combination with complementary noninvasive tests. For example, cardiac catheterization in patients with valvular or congenital heart disease is best performed with full prior knowledge of any noninvasive imaging and functional information. This allows catheterization to be directed and simplified without obtaining redundant anatomic information that is reliably available with echocardiography, cardiac magnetic resonance (CMR) (see Chapter 17), or CT.


Identification of coronary artery disease and assessment of its extent and severity are the most common indications for cardiac catheterization in adults. The information obtained is crucial to optimize selection of mechanical or medical therapy. In addition, dynamic coronary vascular lesions, such as spasm, myocardial bridging, and plaque rupture with thrombosis, can be identified. The consequences of coronary heart disease, such as ischemic mitral regurgitation and left ventricular (LV) dysfunction, can also be defined. During PCI for acute coronary syndromes, patients are studied during evolving acute myocardial infarction, with unstable angina, or in the early period after acute myocardial injury. The optimal timing for catheterization and revascularization has been described in various guidelines3,4,6 (see Chapters 52 and 53).


In patients with myocardial disease and LV dysfunction, cardiac catheterization provides important hemodynamic and coronary artery information. It can be used to evaluate the severity of coronary artery disease and quantify LV and right ventricular (RV) hemodynamics and function. In patients with angina and impaired LV function, noninvasive testing has limitations and coronary angiography is often indicated to differentiate ischemic from nonischemic cardiomyopathy.2 Cardiac catheterization also permits quantification of the severity of both diastolic and systolic dysfunction and differentiation of myocardial restriction from pericardial constriction.


In patients with valvular heart disease, cardiac catheterization is both confirmatory of and complementary to findings on echocardiography and CMR (see Chapter 63). Cardiac catheterization can define the severity of valvular stenosis or regurgitation, particularly when noninvasive studies are inconclusive or the results are disparate from the clinical findings. Knowledge of coronary artery anatomy is necessary in most adults older than 35 years when valve surgery is planned.1 However, catheterization may be unnecessary in some preoperative situations, such as younger patients (<55 years) with atrial myxoma, endocarditis, or acute valvular regurgitation. Identification of congenital anomalies, quantification of the hemodynamic consequences of valvular lesions (such as pulmonary hypertension), and the acute hemodynamic response to pharmacologic therapy can provide useful preoperative information that helps define the risk and response to surgery and permits a more directed surgical approach.1


The current role of cardiac catheterization in certain congenital disease states has been addressed in guidelines for adults with congenital heart disease7 (see Chapter 62). Echocardiography with Doppler and CMR often provide adequate information. Because gross cardiac anatomy can generally be well defined by these methods, catheterization is required only if certain hemodynamic information (e.g., quantification of shunt severity, pulmonary vascular resistance [PVR], and reversibility of pulmonary arterial hypertension with a vasodilator) is needed for confirmation in determining the indications for surgical procedures or if percutaneous interventions are being considered.


There is no true absolute contraindication to cardiac catheterization other than refusal by a competent patient. The procedure can be performed successfully with relatively low risk even in the most critically ill patients. Relative contraindications to cardiac catheterization are summarized in Table 19-1.




Technical Aspects of Cardiac Catheterization





Catheterization Laboratory Facilities


Cardiac catheterization facilities have several venues, including traditional hospital-based laboratories with in-house cardiothoracic surgical programs, hospital-based laboratories without on-site surgical programs, freestanding laboratories, and mobile laboratories. Of the 5099 hospitals in the United States, 4345 (85%) now have cardiac catheterization laboratories and 1061 (21%) provide cardiac surgical services. At present, approximately 75% of cardiac catheterization laboratories have on-site surgical backup. According to a recent joint position paper,9 a cardiac catheterization laboratory with surgical on-site support services allows cardiac catheterization to be performed safely on any patient with heart disease. A hospital with all these services is considered a “full-service” facility. Cardiac surgical capability, as well as other ancillary services, including cardiac anesthesia, is a critical service. With such support a hospital is fully equipped for complex studies and interventions. Although direct surgical intervention is infrequently necessary, such expertise, including equipment, personnel, cardiac anesthesiologists, perfusionists, and cardiac and vascular surgeons, helps support high-risk patients and management of the complications that can arise. High-risk diagnostic studies and all elective percutaneous interventions should be performed in laboratories with on-site surgical facilities. Recommended on-site support services for a full-service facility include cardiac surgery, cardiac anesthesia, critical care unit, vascular services, hematologic consultative and blood bank services, advanced imaging services (echocardiography/Doppler, CMR, CT), mechanical circulatory support services, and endovascular surgery/interventions.9


The goal of freestanding and mobile cardiac catheterization facilities is to reduce cost while offering services in a convenient location for low-risk patients. The safety of mobile catheterization in properly selected low-risk patients appears to be comparable to that in other settings.


As a result of the documented safety and cost-effectiveness of diagnostic cardiac catheterization in the outpatient setting, approximately 50% of hospital-based procedures are currently performed on an outpatient basis. In general, patients who require preprocedural hospitalization for diagnostic catheterization are uncommon. Such patients include those with severe congestive heart failure and those with stage 4 chronic kidney disease requiring additional prehydration. The need for hospitalization to bridge patients in switching from warfarin to heparin has been obviated mainly by the use of low-molecular-weight heparin as an outpatient strategy for anticoagulation, except for patients with mechanical heart valves.1


Noninvasive testing can identify patients who would be more appropriately evaluated in a setting in which cardiac surgery is available, including those with severe ischemia discovered during stress testing, ischemia at rest, highly suspected severe left main or proximal three-vessel disease, critical aortic stenosis, and severe comorbid disease. Most patients can be discharged on the same day within 2 to 6 hours after the procedure.


The most common reason for postprocedural hospitalization is hematomas, which necessitate additional bed rest and observation. In addition, diagnostic findings from the procedure may require hospitalization, including severe left main or three-vessel disease. Other potential indications for postprocedure hospitalization include decompensated heart failure, unstable ischemic symptoms, severe aortic stenosis with LV dysfunction, renal insufficiency requiring further hydration, and need for continuous anticoagulation.


The hybrid cardiac catheterization laboratory has recently gained popularity with the advent of transcatheter valvular and structural heart interventions. Also, combined valvular or coronary artery surgery with PCI is well suited for hybrid suites. The main impetus is to provide high-resolution imaging with the sterility and capabilities of a cardiovascular surgical operating room. Lighting and air exchange must conform to operating room standards. Space requirements are generally larger than those needed for standard operating room or catheterization laboratories to accommodate the multidisciplinary team and equipment. These facilities can be located either in the cardiac catheterization laboratory or in the operating room. Dedicated catheter laboratory and/or operating room personnel are critical to ensure consistent high-quality outcomes after these complex procedures.



Laboratory Procedural Volume.


For proficiency to be maintained, laboratories for adults should perform a minimum of 300 procedures per year. According to the Accreditation Council for Graduate Medical Education guidelines for diagnostic catheterization, physicians in training must spend a total of 8 months and perform more than 300 cases, including more than 200 as a primary operator, to be credentialed for level II diagnostic cardiac catheterization procedures in practice.8 However, the minimum volume for practicing physicians has not been established.9 Regular evaluation with quality assessment of laboratory, physician, nurse, and technologist performance and outcomes is mandatory. The laboratory director should have at least 5 years of catheterization experience. In a laboratory performing PCI, the director should be board-certified in interventional cardiology. The director is responsible for credentialing of physicians; review of laboratory, physician, and ancillary personnel performance; and provision of necessary training.



Equipment.


Equipment for cardiac catheterization includes the radiographic system and physiologic data monitoring, sterile supplies, imaging for vascular access, and an emergency cart and defibrillator. Also necessary is support equipment consisting of a power injector, image processing with digital archiving, viewing stations, and a uniform method of report generation that allows data analysis of outcomes and procedural technique.



Radiographic Equipment.


High-resolution x-ray imaging is required for optimal performance of catheterization procedures. The equipment needed includes a generator, x-ray tube, flat panel detector, expansive modulation, video image capture, image display, and digital archiving.10 The flat panel detector produces a direct digital video signal from the original visible light fluorescence without the intermediate visible light stage.


Immediate review, quantitative computer analysis, image manipulation, road maps, and flicker-free images at low frame rates minimize exposure of patients and personnel to radiation. Transfer of images between laboratories, hospital networks, and physician offices is accomplished with the use of remote secure Internet access. The development of digital imaging and communication standards for cardiac angiography has allowed compatibility among different vendors.



Physiologic Monitors.


Continuous monitoring of blood pressure and the electrocardiogram (ECG) is required during cardiac catheterization. Systemic, pulmonary, and intracardiac pressure is generally recorded with use of fluid-filled catheters connected to strain gauge pressure transducers and then transmitted to a monitor. Equipment for determination of thermodilution cardiac output and blood gas determination, as well as a standard 12-lead ECG, is necessary. Measurement of oxygen consumption for determination of cardiac output with the Fick method should be available in laboratories performing valvular and congenital diagnostic procedures.



Radiation Safety.


The main guiding principle of x-ray exposure is ALARA (as low as reasonably achievable). This implies that no level of radiation is completely safe to patients or providers. The effects of radiation can be classified as either deterministic or stochastic. Both are characterized by a delay between radiation and effect. The delay may be hours to years. Examples of deterministic effects include skin erythema, desquamation, cataracts, hair loss, and skin necrosis. Skin injury is the most common deterministic effect from radiation. Early transient erythema can develop within hours, but most skin injuries do not appear for 2 to 3 weeks after exposure. Stochastic effects are related to probability and are not proportional to dose, although the likelihood of an effect is related to dose. Examples of this effect include neoplasms and genetic defects. The dose-area product is the absorbed dose to air (air kerma) multiplied by the cross-sectional area of the x-ray beam at the point of measurement. It is an approximation of the total x-ray energy delivered to the patient and is a measure of the patient’s risk for stochastic effects.10


Deterministic effects are dose related, which means that below a certain dose, there is no effect. However, when a threshold is exceeded, severity increases with dose. The estimated dose range for cardiac catheterization is 1 to 10 millisievert (mSv), which is the equivalent of 2 to 3 years of natural background radiation. The typical dose is 3 to 5 mSv.10 Another measure of skin dose is the interventional reference point, which is located 15 cm from the isocenter of the x-ray tube and is an estimation of the skin entrance point of the beam.


The basic principles of minimizing radiation exposure include minimizing fluoroscopic beam time for fluoroscopy, using beam collimation, positioning the x-ray source and image reception optimally, using the least magnification possible, rotating the radiographic projection during long procedures to minimize exposure of skin at the entrance port, and recording the estimated patient dose.


For laboratory personnel, the most important factors are maximizing distance from the source of x-rays and using appropriate shielding, including lead aprons, thyroid collars, lead eyeglasses, and movable leaded barriers. Severely angulated views, particularly the left anterior oblique (LAO) view, substantially increase the radiation exposure of operators because of scatter from patients.


A method of measuring radiation exposure of personnel is required. It is recommended that at least two film badges be worn. One should be worn on the outside of the apron at the neck and another under the apron at the waist. The latter monitors the effectiveness of the lead apron. The maximum allowable whole-body radiation dose per year for those working with radiation is 5 roentgen-equivalents-man (rem = 50 mSv), or a maximum of 50 rem in a lifetime.10



Catheterization Laboratory Protocol


Preparation of the Patient for Cardiac Catheterization


Before arrival in the catheterization laboratory, the cardiologist responsible for the procedure should explain the procedure fully, including the risks and benefits, and answer questions from the patient and family. Precatheterization evaluation includes a patient history, physical examination, and ECG. Routine laboratory studies include a complete blood count with platelets, serum electrolyte determinations with creatinine and estimated glomerular filtration rate (eGFR), prothrombin time with international normalized ratio (INR) (in patients receiving warfarin or with hepatic disease), and the partial thromboplastin time (in patients receiving heparin). Important components of the history that need to be addressed include diabetes mellitus (insulin or non–insulin requiring), kidney disease, anticoagulation status, peripheral arterial disease, and previous allergy to contrast media or latex. Full knowledge of any previous procedures, including cardiac catheterizations, PCI, peripheral arterial interventions or surgery, and cardiac surgery, is necessary.


Patients should be fasting for at least 6 hours, and an intravenous line should be established. Oral or intravenous sedation is often administered (e.g., benzodiazepine). Pulse oximetry should be used to monitor respiratory status. Warfarin should be discontinued approximately 3 days before and the INR should be less than 1.8 to minimize risk for bleeding. An INR lower than 2.2 is acceptable for radial artery access.9 In patients receiving dabigatran, use of the medication should be discontinued 24 hours before catheterization in patients with normal renal function and 48 hours before in those with an eGFR higher than 30 and lower than 50 mL/min. A lower eGFR will require several days of cessation. Aspirin and/or other oral antiplatelet agents are continued before the procedure. Patients with diabetes receiving metformin should have use of the medication discontinued the morning of the procedure and not be restarted until renal function is stable for at least 48 hours after the procedure.11 To minimize the risk for contrast-induced nephropathy, all patients should receive hydration before and after the procedure. The amount of hydration is dependent on LV function and baseline fluid status. However, if tolerated, a total of 1 liter of normal saline administered between initiation and completion of the procedure is recommended. Another hydration regimen that has been studied to prevent contrast-induced nephropathy in patients with chronic kidney disease is the use of sodium bicarbonate at 3 mL/kg for 1 hour before the procedure and 1 mL/kg for 6 hours after.12 This regimen was initially reported to be superior to normal saline, but recent data have shown equivalence. Despite this lack of superiority, it is a simple and rapid regimen for prevention of contrast-induced nephropathy.


Those with a previous history of allergy to contrast media need prophylaxis before the procedure.13 A recommended regimen is the administration of either prednisone (50 mg by mouth) or hydrocortisone (100 mg by intravenous push) 12 hours and immediately before the procedure. Cimetidine (300 mg by intravenous push or by mouth), a nonselective histamine antagonist, and diphenhydramine (25 to 50 mg by intravenous push) may also be given. A common misconception is that a history of shellfish allergy predisposes patients to contrast media reactions. Tropomyosin, not the iodine in shellfish, appears to be the allergen.



Catheterization Protocol


A general routine for performing diagnostic catheterization will ensure efficient acquisition of all pertinent data. In general, hemodynamic measurements and determination of cardiac output should be done before angiography to reflect the basal conditions most accurately. However, in a high-risk case, the approach is to acquire the most important information first because of the possibility of patient instability.


Right-heart catheterization should not be performed in all patients undergoing routine coronary angiography because of the low yield in those with suspected coronary artery disease without other known cardiac disease. Right-heart catheterization should include screening oximetric analysis, measurement of intracardiac pressures, and determination of cardiac output. Right-heart catheterization is indicated when a patient has LV dysfunction, heart failure, complicated acute myocardial infarction, valvular heart disease, suspected pulmonary hypertension, congenital heart disease, intracardiac shunts, or pericardial disease.


Although use of a temporary pacemaker is not indicated for routine cardiac catheterization, operators should understand the techniques for proper insertion. Even in patients with an isolated left bundle branch block, right-heart catheterization can generally be performed safely with balloon flotation catheters without causing any additional conduction disturbance. An example of a balloon flotation catheter (Swan-Ganz) is shown in Figure 19-1.




Catheters and Associated Equipment


Catheters used for cardiac catheterization are available in various lengths, sizes, and configurations. Typical catheter lengths vary between 50 and 125 cm, with 100 cm being used most commonly for adult left-heart catheterization via the femoral approach. In patients with a dilated ascending aorta or tortuous ascending or descending aorta, a longer 125-cm catheter is often used. The outer diameter of the catheter is specified in French units, with 1F equaling 0.33 mm. The inner luminal diameter of the catheter is smaller than the outside diameter because of the thickness of the catheter material. Guidewires used during the procedure must be the proper caliber to pass through the inner diameters of both the introducer needle and the catheter. Guidewires are described by their length in centimeters, diameter in inches, and tip conformation. A commonly used wire is a 150-cm, 0.035-inch J-tip wire. Introducer sheaths are specified by the French number of the largest catheter that can pass freely through the inner diameter of the sheath rather than the outer diameter. Therefore a 7F introducer sheath accepts a 7F catheter (7F = 2.31 mm) but has an outer diameter greater than 7F.


Selection of the size of the catheters to be used is determined by balancing the need to opacify the coronary arteries and cardiac chambers adequately and to permit sufficient manipulation of the catheter while limiting vascular complications and allowing earlier ambulation. The most commonly used catheters are 4F to 6F, which permit early ambulation after femoral artery access and generally provide adequate visualization. Smaller catheters require greater technical skill for manipulation and have lower flow rates. Thus their use in patients with tortuous anatomy, large body habitus, or high coronary flow states (e.g., aortic regurgitation) can be challenging. The relationship between sheath size and vascular complications is not clear within the range used for routine diagnostic catheterization. Rather, the arterial puncture technique, anticoagulation status, including the use of thienopyridines and glycoprotein IIb/IIIa receptor inhibitors, and the presence of coagulopathies are more important factors related to vascular complications.14


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Jun 4, 2016 | Posted by in CARDIOLOGY | Comments Off on Cardiac Catheterization

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