Cardiovascular disease is not only the leading cause of morbidity and mortality in Western nations, it is the leading cause of health care expenditures. It is estimated that the cost of the diagnosis and treatment of cardiovascular disease and stroke will exceed $431 billion in 2007 ( ). Cost related to cardiovascular disease is multifactorial with a large component related to the expense of diagnosis. Accurate, rapid diagnosis of cardiac disease is essential for the appropriate triaging and treatment of patients with coronary artery disease.
Clearly, patients with acute coronary syndromes or active infarction require immediate medical support and revascularization. These patients typically do not present a diagnostic dilemma and have characteristic symptoms of chest pain or pressure radiating to the left arm or jaw, diaphoresis, nausea, dizziness and anxiety. ECG changes of ST-segment elevation and elevated serum troponin or creatine kinase muscle-brain type (CK-MB) are demonstrated in these patients. Patients presenting in this manner should be transported emergently to the angiography suite for prompt diagnosis and treatment of obstructive coronary disease.
Patients with atypical presentations or low-intermediate suspicion for coronary disease pose more of a diagnostic dilemma. It is in this patient population that non-invasive cardiac imaging plays a key role in diagnosis and triage. Evaluation of these patients includes clinical history and physical examination, ECG findings, serial enzyme laboratory investigations and some form of non-invasive imaging ( ). This may take the form of exercise stress testing, coronary calcium score ( ), nuclear myocardial perfusion imaging, coronary CT angiography (CCTA) or, occasionally, cardiac magnetic resonance imaging ( ). If all of these investigations are unrevealing, conflicting or inconclusive, the patient may proceed on to conventional catheter angiography.
There is a wealth of literature on the efficacy, sensitivity and specificity of the well established techniques of stress-rest myocardial perfusion imaging, However, to date, few studies have been performed to compare these techniques to newer modalities such as coronary CT angiography. In the original research published by Budoff et al. ( ) in this journal, the authors perform just such a comparison. By using catheter angiography as a gold standard, the authors prospectively evaluated patients with stable angina with myocardial perfusion imaging (MPI), coronary calcium scoring (CAC) and coronary CT angiography. It was the finding of these authors that coronary CT angiography had a higher sensitivity and specificity for obstructive coronary disease than myocardial perfusion imaging, or coronary artery calcium scoring.
Recent data published for coronary CT angiography performed on 64 slice multi-detector row CT (MDCT) scanners have reported sensitivities and specificities of 93% and 97% respectively ( ). The negative predictive value of MDCT coronary angiography has improved from 97% in studies of 16-row detectors to 100% in 64 slice MDCT studies. While these studies demonstrate nearly ideal negative predictive values, the positive predictive values of this imaging modality have not been as remarkable. Studies report a range of positive predictive values as low as 64% ( ) for all evaluable segments. The number of evaluable segments has also significantly increased with the advent of 64-row technology and aggressive beta-blockade ( ).
Myocardial perfusion imaging, in contradistinction, has been demonstrated to have lower sensitivity (approximately 75–80%), specificity (approximately 60–80) ( ) and positive and negative predictive values (approximately 75–80% and 60–80% respectively). The spatial resolution of MPI is also lower than that of CT. The inherent resolution of MPI imaging, even with positron emission tomography CT (PET CT) cannot exceed 1.4 cm ( ) Conversely, CT has a resolution of 0.5 cm ( ).
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