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Left Heart Studies

Invasive Tests
 


Left Heart Cardiac Catheterization
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Cardiac catheterization and coronary angiography

Although the technique and accuracy of non-invasive 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. 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. 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. Coronary angiogram and left ventriculogram findings allows the doctor to identify viable areas of the heart muscle that may benefit from a revascularization procedure (CABG or PCI).  

Before the procedure:

• the cardiologist fully explains the risks and benefits to the patient
• should obtain written consent
• should answer questions asked by the patient or family so as to reduce fears about the procedure
• a complete history, physical examination, complete blood count, blood chemistries, chest X-Ray, 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.

Patients should fast for at least 8 hours before the procedure. Premedication with a mild sedative is common.

Numerous items of disposable equipment are used for the procedure, including various catheters, wires, needles, syringes, introducer sheaths, and stopcocks. Frequently, a special 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, 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.
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. 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.   


• Intraprocedure complications

Hypotension

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.  

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 medical treatment.  

Chest pain

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 i intravenous nitroglycerin, but persistent pain with evidence of myocardial ischemia may indicate the need for urgent revascularization.  

Arrhythmia

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.  

• Major complications

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.  

Death

Death rates from cardiac catheterization have declined steadily over the past 15 years. The incidence of procedure-related death is now approximately 0.08%. The risk of death varies with age; patients older than 60 years and younger than 1 year have an increased mortality rate from catheterization. An 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%).  

Myocardial infarction


The current risk rate for procedure-related 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.   

Stroke

The procedure-related stroke rate was as high as 0.23% in 1973, but it has decreased to 0.06%. 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.  

Infection

Cardiac catheterization is a sterile procedure, thus, the incidence of infections is very low. To eliminate the risk of patient-to-patient infection, the theatre is cleaned between procedures and multiuse drug vials are avoided.  

Allergic reaction

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 rather than the newer agents. These reactions actually may be vasovagal in origin.   

Renal dysfunction

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. Creatinine levels usually begin to rise 2-3 days after contrast exposure and slowly return to baseline within 7 days.

Contrast nephropathy is avoided by limiting contrast volume to the minimum required for completion of the procedure. Low-osmolar contrast agents are 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 may prevent worsening of renal function in patients with renal insufficiency.  

Arrhythmias

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. 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.  

• Vascular complications

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.   

Bleeding

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. Abdominal ultrasound 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. The diagnosis is confirmed by duplex ultrasound. Surgical correction is necessary for large pseudoaneurysms with a wide connection to the parent artery.  

• 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. 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.

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.  


• Left ventriculography

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 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.   

Mitral regurgitation

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.



 
 
 
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