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Clinical use of CT heart scans in patients with possible coronary heart disease (CHD)


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 The patient with symptoms or signs suggestive of coronary heart disease is a very common clinical problem for both cardiologists and primary care doctors. The older, more traditional approach to such patients emphasized the use of functional stress tests ( with plain ECG, nuclear perfusion imaging, or echocardiography) to detect hemodynamically significant stenoses amenable to interventional or surgical treatment.  The major limitation of such tests is that they do not exclude vulnerable plaques which may be hemodyanmically insignificant but are susceptible to rupture, possibly resulting in myocardial infarction or sudden death.

The widespread use of statins and their clinical effectiveness in reducing the morbidity and mortality of CHD, presumably by stabilizing vulnerable plaque, has made the detection of earlier (ie, hemodynamically insignificant and possibly asymptomatic) stages of CHD much more important.  Fortunately, the advent of the 64-slice CT scanner has made possible CT coronary angiography with intravenous contrast injections that can detect CHD in its very earliest stages, allowing the clinician to begin aggressive lipid-lowering  therapy much sooner.

The following flow chart helps illustrate how the clinician might use CT angiography in combination with other testing modalities to most effective assess the patient with suspected CHD. For the sake of simplicity, the chart uses chest pain as the primary symptom of concern, but anginal equivalents such as new exertional dyspnea, frequent ventricular ectopy, or a newly abnormal ECG could be susbstituted and the analysis would be the same.

 

                     ASSESSMENT OF CHEST PAIN 

 

    

                               PATIENTS WITH RELATIVELY LOW RISK OF CHD

 Patients in the left column have minimal or no risk factors for CHD and relatively atypical symptoms. Most, if not all, of such patients can be managed with no testing other than a lipid profile since any stress test that might be done would have a high likelihood of giving a false positive result. When necessary for reassurance, at most a simple ECG stress test should suffice.

 

                     PATIENTS WITH INTERMEDIATE-HIGH RISK OF CHD

Patients in the middle column with intermediate or greater risk of CHD are those most likely to benefit from a CT heart scan because their spectrum of potential disease is the widest. If the scan shows no evidence of CHD, there is clear evidence that they do not not require aggressive lipid-lowering therapy beyond the normal guidelines and no additional testing is necessary no matter how typical their symptoms or high their risk factors.

Alternatively, if the scan shows the presence of CHD in the form of calcific or non-calcific plaque but no significant stenosis, aggressive lipid-lowering therapy (LDL<70) is clearly warranted.

The presence of plaque with at least borderline significant stenosis would warrant additional functional stress testing (nuclear perfusion imaging or stress echocardiography). Those patients who had more typical symptoms or who had already undergone equivocal stress testing would be candidates for catheterization and coronary angiography.

Finally, patients with evidence of plaque and high-grade stenosis would be immediately referred for catheterization and coronary angiography

  

   PATIENTS WITH HIGH RISK FACTORS AND TYPICAL SX OR KNOWN CHD

These patients, in the right-hand column, have a very high pre-test likelihood of CHD and a hemodynamically significant stenosis. Most of these patients would be best referred directly for catheterization and coronary angiography because of the concern that any non-invasive test could give a false-negative result.

Even in this group, though, there are selected patients for whom CT angiography is appropriate. The most obvious are those who refuse catheterization. CT angiography is very useful for assessing patients with prior surgery and multiple by-pass grafts. Because of their size and relative immobility, by-pass grafts are visualized extremely well with CT angiography, sometimes even better than at catheterization.

 

References

 

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