Statement of the Problem
Conventional coronary angiography is the current “gold standard” for diagnosing coronary artery disease. This modality can be used for diagnostic as well as therapeutic purposes. The process is however painful and filled with the potential for many complications. Some of the risks associated with angiography can be overcome by MRI and MSCT. ¹Other than overcoming these risks these methods of diagnosis are also patient-friendly and cost–effective.
A diagnostic procedure for the patient that is more comfortable with the patient experiencing less pain is more likely to have lower rates of cancellation and no show. Further, patients’ showing a higher preference for one diagnostic test over another is likely to influence physician’s recommendations of the tests.. ¹
Purpose of the Study
The purpose of the study is to determine which diagnostic imaging modality, MSCT, MRI, or conventional coronary angiography, patients would prefer to undergo to diagnose coronary artery disease.
Hypothesis
It is expected that patients will find the MSCT procedure much more convenient and less painful to undergo. It is also expected that the sensitivity and specificity of MSCT will be found to be superior to MRI or conventional coronary angiography.
Literature Review
Coronary Artery Disease is often a complication of atherosclerosis. Atherosclerosis results from the narrowing of arteries that have hardened following the build-up of cholesterol plaques. The narrowing may also be caused by thrombi that have formed on plagues. The most common symptom is dyspnea (difficulty in breathing and shortness of breath) and angina.
The most serious consequence of CAD is myocardial infarction. Myocardial infarction commonly known as a heart attack occurs when there is blockage of a coronary artery. This leads to the death of part of the heart muscle (imaginis.com, 2008). Cardiac arrest is also a possible result of CAD.
Among patients who die sudden deaths, about 90 percent of them have two or more narrowed arteries due to atherosclerosis.
CAD is the number one cause of death in both male and female adults in the US and Europe. An estimated, 12,800,000 Americans have CAD while about 500,000 Americans have heard heart attacks resulting from CAD. More than 12 million Americans live with or have a history of angina myocardial infection or both, (American Heart Association, 2005). CAD is also a significant health threat in European countries. About two million people in Europe die due to CAD and CAD-related conditions. The rate of death among CAD patients is high and in Easton, central and Northern Europe than in the western and southern parts of Europe. The death rate for men in Russia is up to eight times high than for France while that for women is about 12 times higher in Russia as compared to France. About, 480,000 Germans have cardiac examination procedures carried out annually (www.imaginis.com, 2008).
CAD has controllable and uncontrollable risk factors. The controllable ones include smoking, a sedentary lifestyle, high levels of blood cholesterol, high blood pressure, obesity, diabetes, and stereo. The uncontrollable ones include genetics, gender, race, and family history.
Diagnosis of CAD is done through physical examination, measurements of blood pressure, measurement of blood cholesterol, electrocardiogram, stress test, chest x-ray, coronary angiography, cardiac magnetic resonance imaging, C T scan (Computerized Tomography), an echocardiogram.
The most commonly used techniques are MRI, CT scan, and angiography which provide a visual picture of the blood vessels, helping to identify narrowed vessels.
CT has been reported to be superior to both angiography and MRI in the diagnosis of CAD. In a study involving 129 patients, 108 patients had 430 vessel sex examined before going through angiography. They were examined using MRI and Multislice CT. According to the study, Multislice CT had up to 92% sensitivity in the detection of CAD while the sensitivity for MRI was 74%. Where there were greater clinical stencils, the difference between CT and MRI was even more significant. A patient survey indicated that about 73 percent of the patients preferred CT or MRI (Dewey et al, 2006).
Another study involving 142,153 patients who had either CT myocardial perfusing imaging (MPI) carried out on them yielded results in favor of CT. The study marched the patients using various categories, about 11 of demographic and risk states. These results indicate that the patients who undergo CT incur fewer expenses making CT the more cost-effective diagnosis tool (Cardiovascular Business News, 2008).
CT involves the utilization of radiation and contrast agents introduced intravenously. It has a high negative predictive value and is therefore has the potential to be a very useful tool in ruling out CAD amongst subjects who have a low likelihood for CAD (Reuters Health Information, 2006). CT scan is a non-invasive procedure used to visualize coronary arteries for blockage. There are various kinds of CT scans and there are more like a progression from one to another with the latter having higher sensitivity. The ultrafast CT scan is also known as the electron CT scan (EBCT) is a version type of the CT scan that was used earlier.
The EBCT scan is not very useful in the citation of accurate images of a coronary artery. EBCT scans indicate a patient’s calcium score. The calcium score is a reflection of the calcium deposits present on the coronary arteries living. The greater the amount of calcium score. The calcium score is a reflection of the calcium deposits present on the coronary arteries living. The greater the amount of calcium present, the more the CAD is present.
This CT scan, however, does not indicate the presence of actual, individual blockages that would be significant in the coronary arteries. CT technology has improved to include CT images with gantries that rotate. This enables greater accuracy in the visualization of arteries. Consequently, the blockages if any are seen with much clarity. In the case of Multislice CT scans (MSCT), the scans increase in quality as the camera takes more slices. The high negative predictive value of MSCT means that for an individual with blockages that are significant in the arteries, the probability that the MSCT scan will detect is upwards of 90 percent (Rich, 2008).
The MSCT has limitations, however. To begin with, it is not able to visualize the coronary tree in its entirety. Studies show that only about 71 percent of the coronary artery is visualized by the CT while others claim that 88% of the tree can be evaluated by the CT. the downside here is that there are chances of MSCT missing existing blockages that range from 12% to 29%. Other limitations in the use of MSCT include patient requirements such as a regular resting heart rate, a heart rate not higher than 60-70 beats in one minute. A patient with atrial fibrillation would thus not be a good candidate for MSCT. Allergy to the contrast dye also disqualifies some patients from using this diagnostic test. Patients with a large number of calcium deposits do not benefit much from the procedure since the resolution of the arteries is generally poor. The patient is also exposed to large amounts of radiation (Garcia et al, 2006).
MRI combines 2Dand 3D techniques with advanced magnetic hardware. The MRI machine converts energy produced by the hydrogen atom nucleus when it is exposed to variations of the magnetic field. This energy is converted by the machine to energy. Hydrogen nuclei are used because of the abundance of hydrogen in the form of water in the human body. The MRI image is usually 3D and can be sliced in any direction, allowing for differences in tissues to be detected. A difference in the rate of blood flow or tissue viability will lead to different emissions of energy. This is important in the detection of areas with compromised blood flow as in coronary artery disease or in the detection of areas that have undergone myocardial infarction (Fogoros, 2003).
The MRI has the disadvantage of inducing claustrophobia in an estimated 5 percent of patients. Their ECG gets distorted meaning that patients who are critically ill cannot undergo the MRI examination. Patients who have devices like pacemakers, defibrillators, and artificial heart valves cannot have cardiac MRIs done on them (Fogoros, 2003). All these factors influence the patient’s degree of concern, comfort, degree of helplessness, pain, willingness to undergo the procedure again, and overall satisfaction. When these factors are considered then the MRI becomes a choice that many patients would not make.
Coronary angiography is the most common method of diagnosing CAD. It is an invasive procedure carried out in cardiac catheterization laboratories. The examination involves placing a catheter in one of the major blood vessels. A dye of radio-opaque material is then injected to enhance the creation of the image of the heart and coronary arteries. The patient is usually given a sedative to help them relax. Angiography is not only useful for the diagnosis of CAD; it is also utilized in providing a guide to the progress of treatment. Sometimes when a blockage is found the doctor can decide to open the blockage thus providing diagnosis and treatment in one procedure (Gandelman, 2006).
Often, the finding in CAD is a relatively smooth vessel or a slight irregularity of a tapered narrowing of the artery. In angiography, the occlusion as a result of CAD is not specific where there are other causes like thromboembolism or atherosclerosis. These two conditions may present similar characteristics in embolism making it a limited method. MRI and MSCT have no such limitation and MRI is especially useful in this aspect making it a more accurate method. Some of the risks associated with coronary angiography include arrhythmias, tamponade, hemorrhage, stroke, hematoma formation, and decreased blood pressure. These possible complications make the condition worse for the patient who may have CAD. In addition, they increase the patient’s anxiety especially when the patient is fully aware of the risks involved. The invasive nature of the procedure comes with automatic risks such as the risk for infection, bleeding, and pain at the site of venipuncture and insertion of the intravenous line. Plastic catheters may also cause damage to the blood vessels. The formation of blood clots on catheters that could late block the vessels in other body parts is also another possible risk. The contrast dye is not only a worrying factor to patients who are allergic to it but also to those patients with conditions like diabetes as it has the potential to cause damage to the kidneys (Gandelman, 2006).
Method
This study was approved by the institutional review board and the Federal Department of Radiation Protection. The patients who participated were required to give written consent. A purposive sampling method was used, where only patients with suspected CAD were chosen. The patients also had no contraindications to MSCT, MRI, or coronary angiography.
One hundred twenty patients (mean age 60 ± 9 years) participated in the study at the University of Chicago Medical Centers.
Each patient first underwent MSCT and MRI, before one day later undergoing conventional coronary angiography. The study was conducted at the University of Chicago Medical Centers. The study group was composed of 120 patients whose mean age was 60 ± 9 years. A purposive sampling method was used, choosing only patients with suspected coronary artery disease and without contraindications to MSCT, MRI, or coronary angiography. The patients first underwent MRI and MSCT before they could undergo coronary angiography. A GE Light speed 16 slice scanner was used to perform the MSCT. The contrast used was nonionic Omnipaque 350. A dual-head Med-Rad power injector was used to inject 100mls of contrast at a flow rate of 3.5mls/s. Radiation exposure was estimated at 12.6mSv. A Siemens 1.5TMRI scanner was used to perform the MRI using a dedicated cardiac coil. After 10minutes, five patients could not go on with the exam due to claustrophobia. They were included in the study.
The transfemoral approach was used to perform angiography with an average of 107mls of iodinated contrast is administered. Radiation exposure was estimated at 11.4mSv. The local anesthetic used was lidocaine. After angiography, each patient had a pressure dressing applied for 6hours. All the patients had to lie in supine positions for 12 hours during angiography. The design of the study was a posttest – only nonexperimental design with no control group (Trochim, 2005). The patients answered questionnaires a day after the completion of the three diagnostic exam procedures. The questionnaire used a 1-to-5 rating Likert response scale. To eliminate bias the wording in the questions was the same for each diagnostic test. Open-ended questions were used to determine the advantages and disadvantages of each diagnostic test from the patient’s viewpoint. Any questions the patients had were answered by the researchers who were present as the patients filled in the questionnaires.
Discussion of Expected Results
The issues being measured were patients’ concern, comfort, degree of helplessness, pain, willingness to undergo the procedure again, and overall satisfaction. It was expected that patients would prefer to undergo MSCT over MRI and conventional coronary angiography. MRI rated less comfortable than MSCT. Conventional coronary angiography was rated more painful than both MRI and MSCT. MSCT was perceived as noninvasive and therefore painless. It was also perceived as fast. Thus it was rated as the most preferable of the three modalities. MRI though rated as less painful than conventional coronary angiography was less comfortable than MSCT because it took longer and was more confining. Conventional coronary angiography was perceived as more painful, but the treatment of stenoses could be administered at the same time.
Significance to Knowledge/Practice
Coronary artery disease is a major public health issue in the United States. It is, therefore, necessary to improve patient compliance to diagnosis and treatment. Conventional coronary angiography is the current standard diagnostic procedure used in the detection of coronary stenoses. Diagnosis of coronary artery disease can be made more cost-effective with a painless, non-invasive approach such as MSCT or MRI. These approaches have also been found to be more accurate and valuable in differentiating plaques than angiography. With patients aware of these facts they are more likely to choose these diagnostic methods (MRI or MSCT) thus increasing the rate of patient compliance and improving the prognosis for CAD with early interventions as a result of early detection of the condition.
Conclusion
The higher degree of accuracy when using MRI and MSCT has been backed by much evidence from research. These two methods are consequently better choices for the patient when additional qualities such as non-invasiveness and lack of pain are added. The MSCT has the advantage of being faster without the uncomfortable characteristic of claustrophobia. MSCT, therefore, shows great promise in the future of diagnosing coronary artery disease.
The safety and reliability of MSCT coupled with its high negative predictive value make this modality a fast and reliable means for evaluating chest pain in the emergency department. MSCT could therefore become the new gold standard for diagnosing coronary artery disease over MRI or conventional coronary angiography.
References
Cardiovascular Business NEWS, 2008, Web.
Caso V, Bogousslavsky J, 2005, Handbook on Cerebral Artery Dissection Front Neurol Neurosci Basel, Karger, 2005, vol 20, pp 102-118 (DOI: 10.1159/000088155) Baumgartner RW, Paciaroni M (eds).
Dewey M, Taigas, Schnapauff D, Laule M, Borges A, Wemecke K, Schink T, Baumann, G. RutschW, Rogalla P, Taupitz M Hamm B2006, Noninvasive Detection of Coronary Artery Stenoses with Multislice Computed Tomography or Magnetic Resonance Imaging Fogoros R, 2003 Cardiac MRI – part 3 By, Web.
Gandelman G, 2006, Coronary angiography. Web.
Garcia MJ, Hoffmann MHK Lessick J, et al, 2006, Accuracy of 16-row multidetector computed tomography for the assessment of coronary artery stenosis JAMA 2006; 296:403-411.
Reuters Health Information, 2006 CT Superior to MRI for Detecting Coronary Artery Disease Annals of Internal Medicine, 145, 407-415Ann Intern Med 2006;145:407-415,466-467.