Historical perspective of cardiac catheterization
In 1844, Claude Bernard passed a catheter into both the right and left ventricles of a horse's heart via a retrograde approach from the jugular vein and carotid artery. He was the first to perform a scientific study of cardiac physiology, and he set the stage for cardiac catheterization as it is known today.
In 1929, in Eberswalde, Germany, a 25-year-old surgical trainee named Werner Forssmann was the first to pass a catheter into the heart of a living person—his own. He passed the catheter into his right atrium via the left antecubital vein under fluoroscopic guidance and then climbed the stairs to the radiology department to undergo a chest radiograph. His efforts were not rewarded but, rather, stimulated considerable opposition and bitter criticism; however, in 1956, he shared the Nobel Prize in medicine with other pioneers of invasive cardiology.
Further developments in invasive cardiology were slow until the work of Andre Cournand and Dickenson Richards, who performed the first comprehensive studies of right heart physiology in humans.
In 1947, Louis Dexter expanded the clinical use of right heart catheterization with studies in patients with congenital heart disease and identified the pulmonary capillary wedge pressure as a useful clinical measurement. By this point, the value of hemodynamic measurements was being fully realized, and further developments came rapidly.
Cardiac catheterization and coronary angiography
Although the technique and accuracy of noninvasive testing continues to improve, cardiac catheterization remains the standard for the evaluation of hemodynamics. Cardiac catheterization helps provide not only intracardiac pressure measurements, but also measurements of oxygen saturation and cardiac output.1 Hemodynamic measurements usually are coupled with a left ventriculogram for the evaluation of left ventricular function and coronary angiography.
Coronary angiography remains the criterion standard for diagnosing coronary artery disease and is the primary method used to help delineate coronary anatomy.2 In addition to defining the site, severity, and morphology of lesions, coronary angiography helps provide a qualitative assessment of coronary blood flow and helps identify collateral vessels. Correlation of the coronary angiogram and left ventriculogram findings permits identification of potentially viable areas of the myocardium that may benefit from a revascularization procedure. Left ventricular function can be further evaluated during stress using atrial pacing, dynamic exercise, or pharmacologic agents.
Cardiac catheterization is a procedure undertaken for the diagnosis of a variety of cardiac diseases. As with any invasive procedure that is associated with important complications, the decision to recommend cardiac catheterization must be based on a careful evaluation of the risks and benefits to the patient.
Indications for cardiac catheterization are as follows:
- Identification of the extent and severity of coronary artery disease and evaluation of left ventricular function
- Assessment of the severity of valvular or myocardial disorders such as aortic stenosis and/or insufficiency, mitral stenosis and/or insufficiency, and various cardiomyopathies to determine the need for surgical correction
- Collection of data to confirm and complement noninvasive studies
- Determination of the presence of coronary artery disease in patients with confusing clinical presentations or chest pain of uncertain origin
With the exception of patient refusal, cardiac catheterization has no absolute contraindications. Clearly, the risk-to-benefit ratio must be considered because a procedure associated with some risk should be contraindicated if the information derived from it is of no benefit to the patient. Relative contraindications are as follows:
- Severe uncontrolled hypertension
- Ventricular arrhythmias
- Acute stroke
- Severe anemia
- Active gastrointestinal bleeding
- Allergy to radiographic contrast
- Acute renal failure
- Uncompensated congestive failure (patient cannot lie flat)
- Unexplained febrile illness and/or untreated active infection
- Electrolyte abnormalities (eg, hypokalemia)
- Severe coagulopathy
Note that many of these factors can be corrected before the procedure, thereby lowering the risk. This always should be considered unless the procedure is being performed in an emergency situation.
Numerous items of disposable equipment are used for the procedure, including various catheters, wires, needles, syringes, introducer sheaths, and stopcocks. Frequently, a Swan-Ganz catheter is used for measuring right heart pressures, collecting blood to measure oxygen saturation in various chambers, and determining cardiac output. Pressure measurements within the left ventricle usually are obtained using a pigtail catheter (see image below), and this same catheter is used for left ventricular and aortic angiography. A wide variety of preformed catheter shapes exist for coronary and bypass graft angiography. The outer diameter of a catheter is measured in French units (F); 1 F is 0.33 mm. The inner diameter of the catheter is smaller than the outer diameter because of the thickness of the catheter material.
Decisions about which catheter to use are based on several factors, including (1) the vascular and heart anatomy, (2) the necessity to adequately opacify the coronary arteries and cardiac chambers in different clinical situations, (3) the extent to which the catheter must be manipulated and the desire to limit vascular injury and complications, and (4) whether arterial access is obtained via the femoral artery or via an upper extremity artery. Larger-diameter catheters (7-10F) allow for greater catheter manipulation and excellent visualization, but they have a higher potential for trauma to the coronary or peripheral vasculature. In contrast, smaller catheters (4-6F) are less traumatic and permit earlier ambulation after catheterization, but contrast delivery may be limited in certain situations, thus compromising the quality of the procedure. The 6F diagnostic catheter is used widely for routine angiography because it has a good balance of the necessary requirements.
Although not a necessity, a short vascular access sheath often is used to facilitate arterial access and multiple catheter exchanges, which often are necessary. All catheters and sheaths are advanced over a guidewire to diminish the chance of trauma to the vasculature. A commonly used wire is a 150-cm, 0.035-in J-tipped guidewire.
Preparation of the patient for cardiac catheterization
Before the procedure, the responsible cardiologist should fully explain the risks and benefits to the patient, should obtain written consent, and should answer questions asked by the patient or family. A close physician-patient relationship is important to reduce fears about the procedure. Before the procedure, a complete history, physical examination, complete blood count, blood chemistries, chest radiograph, and ECG should be obtained.
Special attention should be given to identifying patients with insulin-dependent diabetes mellitus, renal insufficiency, peripheral vascular disease, contrast allergy, or long-term anticoagulation use because these conditions are associated with a higher risk of procedure-related complications. Appropriate therapies before the procedure can minimize these risks. For example, adequate hydration before the contrast load will minimize the risk of contrast-induced nephropathy3 and pretreatment with corticosteroids will diminish the likelihood of an allergic reaction to contrast. Evidence is strong that pretreatment with sodium bicarbonate, theophylline, and acetylcysteine are nephroprotective.
Patients should fast for at least 8 hours before the procedure. Premedication with a mild sedative is common, and some operators administer diphenhydramine or a narcotic.
Technique and approach
In the early days of cardiac catheterization, access to the arterial system was obtained by direct exposure of the brachial artery and insertion of the catheters under direct visualization. After the procedure, the arteriotomy and then the skin were sutured closed. Although this classic brachial approach still is used by some operators, the majority of procedures now are performed using a percutaneous approach from the femoral, radial, brachial, or axillary artery. Right heart catheterization now is commonly performed from the femoral, internal jugular, or subclavian veins using percutaneous access methods.
Arterial access from the upper extremity (modified Sones method)
The classic brachial artery technique was developed by Mason Sones, MD and thus often is referred to as the Sones method. Although surgical exposure of the brachial artery still is used by some operators, percutaneous access now is used commonly. A 5F or 6F sheath is inserted into the brachial artery, and catheters are maneuvered through the axillary and subclavian arteries into the ascending aorta. Coronary angiography is performed using either a Sones catheter, which requires deflection of the catheter tip off the aortic valve cusps, or a variety of preformed catheter shapes.
Alternatively, access can be obtained from the axillary artery or radial artery. Access from the axillary artery avoids the potential for injury to the median nerve and provides a better platform for compression of the artery against the humerus to obtain hemostasis. Obtaining access from the radial artery is increasing in popularity. Performing an Allen test before the procedure is necessary to insure continuity of the arterial arch in the hand should the radial artery occlude during or after the procedure. Standard catheters may be used from the radial approach, and several new shapes have been developed to facilitate easy cannulation of the coronary arteries. The main advantage of the radial approach is a low incidence of serious vascular complications and the ability to mobilize the patient quickly after the procedure. The disadvantages of the radial approach are a longer learning curve for the operator and occasional severe arterial spasm, which impairs manipulation of the catheter.
In general, arterial access from the upper extremity is preferred if the patient has important iliac or femoral artery atherosclerosis, prior bypass grafting of these same vessels, or severe obesity rendering the normal landmarks for access difficult to appreciate. Access sites are shown in the illustration below.
Arterial access from the lower extremity
The common femoral artery is the only access site used in the lower extremity. Catheters used for performing coronary angiography via the femoral artery were developed by Melvin Judkins, MD, and thus, the method often is referred to as the Judkins technique. This widely used method requires separate preformed catheters for the right and left coronary arteries. A pigtail catheter frequently is used for measuring left heart pressures and performing a left ventriculogram. The images below show Judkins catheters in position.
Proper access to the common femoral artery is critical for this technique (see image below). Vascular complications are increased if the arterial puncture is made either above or below the common femoral artery. The main advantages to this method are its ease and substantial safety record. The main disadvantage is the need for an extended (2-6 h) period of bedrest after completion of the procedure. Several types of arterial closure devices now are available that provide rapid hemostasis and shorten the period of bedrest considerably. However, complication rates with these closure devices are similar to conventional manual compression.
Because of the smaller-diameter arteries in the upper extremity and thus the more occlusive nature of the catheters, anticoagulation is required for the procedure and unfractionated heparin is used frequently. Many operators also administer heparin when access is from the femoral artery, especially if the procedure is prolonged and several catheter exchanges are required.
Additional vascular approaches used for cardiac catheterization
Rarely, severe atherosclerotic disease may affect both the upper and lower extremities and preclude vascular access at the usual sites. Access to the descending aorta can be obtained via a translumbar approach, and coronary angiography can be performed using the standard catheter shapes.
Catheterization of the left atrium and left ventricle can be performed using a transseptal approach. This technique involves puncture of the intra-atrial septum with a needle followed by advancement of a catheter into the left atrium and left ventricle. Transseptal catheterization is used in patients with mechanical aortic valves or if obtaining a true left atrial pressure is necessary. This technique requires a firm understanding of cardiac radiographic anatomy to avoid puncturing adjacent structures such as the free wall of the right atrium, the coronary sinus, or the aortic root. If left ventricular hemodynamics are necessary in patients with mechanical valves in both the aortic and mitral position, a direct left ventricular puncture may be the only option.
Transient hypotension may occur when large volumes of ionic contrast agents are administered and often is more prominent if the ventricular filling pressures are low. This usually requires no treatment. Other causes of important hypotension require quick investigation and treatment. Ventricular filling pressures can be quickly measured and corrected by volume administration if low. Concurrent drug therapies, such as intravenous nitroglycerin, should be considered and regulated if necessary. Occult blood loss from a retroperitoneal hematoma should be evaluated if hypotension persists, and a vasopressor agent should be administered if central perfusion is critically compromised.
Congestive heart failure
Due to the osmotic effects of the contrast agents and fluid administration during the procedure, congestive heart failure may develop, especially in patients with marginal left ventricular function. This may require aborting the procedure and instituting treatment with oxygen, diuretics, and nitroglycerin.
Chest pain may occur, especially during coronary angiography. Some patients are sensitive to the vasodilator effects of the contrast and may experience mild chest discomfort during each dye injection, even in the absence of underlying coronary artery disease. However, in patients with important coronary artery disease, myocardial ischemia with pain and ST-segment changes may occur. This frequently resolves with sublingual or intravenous nitroglycerin, but persistent pain with evidence of myocardial ischemia may indicate the need for urgent revascularization.6
Minor arrhythmias (eg, atrial or ventricular premature beats, brief episodes of supraventricular tachycardia) are common and usually resolve without treatment. Ventricular tachycardia or fibrillation is a rare occurrence but requires prompt defibrillation.
The risk of a major complication during diagnostic cardiac catheterization is less than 1-2%. The risk-to-benefit ratio strongly favors performance of this procedure as part of the evaluation and treatment of potentially fatal or lifestyle-limiting cardiac disease in appropriately selected patients. In a large series reported from the Society of Cardiac Angiography and Interventions Registry, the multivariate predictors of complications were shock, acute myocardial infarction (MI) within the past 24 hours, renal insufficiency, cardiomyopathy, aortic and mitral valve disease, poorly compensated congestive heart failure, severe hypertension, and unstable angina.
Death rates from cardiac catheterization have declined steadily over the past 15 years. The incidence of procedure-related death is now approximately 0.08%. A high-risk subgroup can be defined based on characteristics identified in multiple large series. The risk of death varies with age; patients older than 60 years and younger than 1 year have an increased mortality rate from catheterization. New York Heart Association functional class IV is associated with nearly a 10-fold increase in mortality compared with classes I and II. A similar increase in risk is observed in those with severe narrowing of the left main coronary artery and poor left ventricular function (ie, left ventricular ejection fraction <30%).
Patients with valvular heart disease, renal insufficiency, insulin-dependent diabetes mellitus, peripheral vascular disease, cerebrovascular disease, or pulmonary insufficiency also have an increased incidence of death and major complications from left heart catheterization. Mortality is especially high in those with preexisting renal insufficiency who have further deterioration of renal function within 48 hours after the procedure, particularly when dialysis is required.
The current risk rate for procedure-related myocardial infarction (MI) is less than 0.03%. The risk of precipitating an MI is influenced by patient-related and technique-related variables. Risk factors that predispose patients to an MI during the procedure include (1) recent unstable angina or non–Q-wave infarction, (2) severe of coronary artery disease, and (3) the presence of important comorbidities.
In high-risk patients, serial ECGs and cardiac enzyme measurements may be considered following the procedure.
The procedure-related stroke rate was as high as 0.23% in 1973, but it has decreased to 0.06% in contemporary registries. Although incidence of stroke has decreased, it is one of the most devastating complications of cardiac catheterization. A stroke may not always be apparent during the procedure. The first symptoms may develop hours after the procedure is completed when atherosclerotic debris loosened from plaques in the proximal aorta finally break free and embolize. Maintain a very high level of suspicion, and evaluate patients after the procedure to assess any neurologic changes.6
High-osmolar contrast agents in the carotid arteries may cause transient neurologic deficits.
Cardiac catheterization is a sterile procedure, thus, the incidence of infections is very low. The American College of Cardiology/American Heart Association task force does not mandate full surgical scrubbing and attire for the femoral approach, but it does recommend it for the brachial approach, which has a 10-fold higher infection risk (0.62% vs 0.06%). Special care should be used in patients with femoral bypass grafts because these patients are prone to life-threatening infections. To eliminate the risk of patient-to-patient infection, the laboratory should be cleaned between procedures and multiuse drug vials should be avoided. Fever occurring after the procedure usually is not due to infection, but rather, it is due to phlebitis or often is unexplained. Pyrogen reactions as a cause for fever are now very uncommon because almost all of the catheters used are single-use disposable devices.
Allergic reactions during cardiac catheterization may be precipitated by local anesthetics, iodinated contrast agents, protamine sulfate, and latex exposure. Allergies to local anesthetic usually occur with the older agents (eg, procaine) rather than the newer agents. These reactions actually may be vasovagal in origin, caused by preservatives in the older ester agents. Some centers perform skin testing prior to the procedure to avoid reactions.
Reactions to iodinated contrast agents occur in approximately 1% of patients. This reaction is not a true anaphylactic reaction but, rather, the result of direct complement activation and thus is an anaphylactoid reaction. Symptoms include sneezing, urticaria, angioedema, bronchospasm, and profound hypotension. The risk of a contrast reaction is increased in patients with other atopic disorders, multiple other allergies, or history of a prior reaction to contrast agents.
To decrease the risk of contrast reactions, high-risk patients should be premedicated with corticosteroids and a nonionic contrast agent should be used. Some physicians also administer H1 and H2 receptor blockers. Severe reactions usually are reversed by an intravenous injection of dilute epinephrine.
Protamine sulfate is now rarely given to reverse the anticoagulant effect of heparin. However, if it is used, serious allergic reactions with profound hypotension can occur. Such reactions are reported to be more frequent in patients with diabetes who previously received neutral protamine Hagedorn (NPH) insulin. The prior long-term exposure to protamine is thought to sensitize the patient to protamine.
Latex-induced allergic reactions are being recognized more frequently. They usually are local, although systemic reactions may occur. These can be avoided by the use of latex-free materials in sensitive patients.
Renal dysfunction is a potential complication of any angiographic procedure. Approximately 5% of patients experience a transient rise in plasma creatinine concentration (>1 mg/dL) after contrast exposure. Patients with preexisting renal insufficiency, multiple myeloma, dehydration, or those taking nephrotoxic medications are at an increased risk. The risk of contrast-induced nephropathy is not increased in patients with diabetes who have normal renal function, but patients with diabetes who have impaired renal function are at high risk. Creatinine levels usually begin to rise 2-3 days after contrast exposure and slowly return to baseline within 7 days. Contrast-induced renal failure usually is nonoliguric, but dialysis occasionally is necessary.
Approximately 1% of patients eventually require long-term dialysis.
Contrast nephropathy can be avoided by limiting contrast volume to the minimum required for completion of the procedure. Low-osmolar contrast agents should be used because these appear to have less renal toxicity than high-osmolar agents.
Although many therapies have been tried, the mainstay of prevention is adequate hydration with normal or half-normal saline before and after the procedure. A recent study demonstrated that premedication with N -acetylcysteine (Mucomyst) may prevent worsening of renal function in patients with renal insufficiency.
Systemic cholesterol embolization is another cause of renal failure after cardiac catheterization. This occurs in approximately 0.15% of patients, mostly in those with severe atherosclerosis. Renal failure in these patients tends to develop slowly over weeks compared with contrast-induced nephropathy, which develops over several days. The hallmark of cholesterol embolization is peripheral embolization resulting in livedo reticularis, foot pain, and purple toes. Episodic hypertension, transient eosinophilia, and hypocomplementemia usually precede the signs of embolization. Treatment is purely supportive, and approximately half of these patients progress to renal failure.
Arrhythmias and conduction disturbances can occur during cardiac catheterization. Most are of little clinical significance except for asystole or ventricular fibrillation. Atrial fibrillation usually is well tolerated but may provoke hemodynamic decompensation in patients with severe coronary disease, hypertrophic cardiomyopathy, aortic stenosis, or severe systolic dysfunction.
Prompt treatment by cardioversion prevents progressive decompensation due to the arrhythmia. Ventricular tachycardia and/or fibrillation occurs in approximately 0.4% of patients. These arrhythmias may result from catheter manipulations or the injection of contrast directly into a coronary artery or bypass graft. Vigorous contrast injection into the conus branch of the right coronary artery, which supplies the right ventricular outflow tract, has a high likelihood of provoking ventricular fibrillation.
Bradycardia occurs commonly at the end of a right coronary artery injection performed using high-osmolar agents. Forceful coughing usually helps clear the contrast from the coronary arteries, supports aortic pressure, and restores normal cardiac rhythm. Bradycardia and hypotension also may occur during a vasovagal reaction. Other symptoms of a vasovagal reaction are yawning, nausea, sweating, and hypotension. The 2 most common times for this to develop are during the administration of local anesthesia in the groin and after the application of pressure to obtain femoral artery hemostasis. Intravenous fluids and atropine are the treatments for a vasovagal reaction.
Complications at the catheter insertion site are among the most common problems observed after cardiac catheterization. These include acute thrombosis, distal embolization, arterial dissection, pseudoaneurysm, or bleeding.
Predisposing factors for arterial thrombosis include a small vessel lumen, peripheral vascular disease, diabetes mellitus, and female sex. Arterial thrombosis is a greater concern with brachial access, and thus, heparin is a requirement. Consultation with a vascular surgeon is necessary in case paresthesia or reduced distal pulses occur following catheterization.
Bleeding is the most common vascular complication. This may simply result in a local hematoma of little clinical significance. However, severe blood loss may develop if bleeding occurs in the retroperitoneal space. Unexplained hypotension and a decreasing hematocrit level should suggest the possibility of a retroperitoneal hematoma. Abdominal sonography or CT scanning usually is diagnostic.
Pseudoaneurysm is another potential cause of important groin bleeding and must be recognized.
A pseudoaneurysm develops if a connection persists between a hematoma and the arterial lumen. It presents as a pulsatile mass, sometimes with a systolic bruit. The diagnosis is confirmed by duplex ultrasonography. Management often is conservative, using prolonged compression or thrombin injection in selected patients. Surgical correction is necessary for large pseudoaneurysms with a wide connection to the parent artery.
Bleeding from the arterial puncture may track into the adjacent venous puncture, forming an arteriovenous fistula and a continuous bruit. Many of these are small and resolve spontaneously. Surgical repair is required to fix enlarging fistulae before hemodynamic compromise develops.
Mitral and aortic stenosis
Determining the severity of a valvular stenosis based on the pressure gradient and flow across the valve is an important aspect of the evaluation in patients with valvular heart disease. The measurement of the pressure gradient alone often is insufficient to distinguish significant from insignificant valvular stenosis. In patients with aortic stenosis, a true transvalvular pressure gradient should be obtained whenever possible. Although measuring the gradient between the left ventricle and the femoral artery is convenient, downstream augmentation of the pressure signal and delay in pressure transmission between the proximal aorta and femoral artery may alter the pressure waveform and introduce errors. This is especially important in patients with a low pressure gradient and cardiac output.
In many patients, left ventricular-femoral artery pressure gradients may suffice as an estimate of the severity of aortic stenosis, especially if the gradient is high and the cardiac output is preserved. The normal aortic valve area is 2.6-3.5 cm2 in adults. Valve areas of 0.8 cm2 or smaller represent severe aortic stenosis.
In patients with mitral stenosis, the valve gradient usually is measured using the left ventricular and pulmonary capillary wedge pressure. The pulmonary wedge pressure tracing must be realigned with the left ventricular tracing for accurate mean gradient determination. However, the most accurate method uses the left atrial and left ventricular pressure. This requires a transseptal catheterization approach. Tracings are shown in the images below (aortic stenosis, first image; mitral stenosis, second image).
The normal mitral valve area is 4-6 cm2, and severe mitral stenosis is present with valve areas smaller than 1.0-1.2 cm2.
This technique is used to define the anatomy and function of the left ventricle and related structures in patients with congenital, valvular, coronary, and myopathic heart disease. It provides valuable information about global and segmental left ventricular function, mitral regurgitation, ventricular septal defect, and hypertrophic cardiomyopathy. The ventriculogram findings can be analyzed qualitatively and quantitatively. The analysis should use a normal sinus beat if possible because ectopic and postectopic beats yield inaccurate information about ventricular function. The ejection fraction may be estimated visually or computed using the area-length method to derive actual end-diastolic and end-systolic volume estimates.
Segmental wall motion also can be visually graded as normal, hypokinetic, akinetic, or dyskinetic or quantified using several computer algorithms.
The severity of mitral regurgitation can be graded based on the amount of contrast regurgitation from the left ventricle through the incompetent mitral valve into the left atrium, using the opacification of the left atrium as a guide. The opacification is graded as follows:
- Grade 1+ (mild): Regurgitation essentially clears with each beat and never opacifies the entire left atrium.
- Grade 2+ (moderate): Regurgitation does not clear with 1 beat and opacifies the entire left atrium after several beats.
- Grade 3+ (moderately severe): The left atrium is opacified completely and achieves equal opacification to the left ventricle.
- Grade 4+ (severe): The entire left atrium is opacified within 1 beat and becomes denser with each beat, with associated refluxing into the pulmonary veins during systole. See image below.
Acute severe mitral regurgitation. Image courtesy of Olurotimi Badero, MD and www.tctmd.com.
An estimate of the degree of valvular regurgitation may be obtained by computing the regurgitant fraction (RF). The difference between the angiographic stroke volume and the forward stroke volume is the regurgitant volume. Angiographic stroke volume is computed from the left ventriculogram findings, and forward stroke volume is derived from cardiac output as determined by the Fick or thermodilution method and the heart rate. The RF is that portion of the angiographic stroke volume that does not contribute to the net cardiac output. RF is computed as the regurgitant stroke volume divided by angiographic stroke volume.
- An RF of 20% is approximately equivalent to grade 1+ regurgitation described visually.
- An RF of 21-40% is equivalent to grade 2+ regurgitation.
- An RF of 41-60% is equivalent to grade 3+ regurgitation.
- An RF of 60% or more is equivalent to grade 4+ regurgitation.