Wednesday, March 24, 2010

Low Diagnostic Coronary Angiography Yields: Perhaps we need a higher threshold to perform

Low Diagnostic Coronary Angiography Yields:
Perhaps we need a higher threshold to perform
Dr David KL Quek, FNHAM, FACC (Published NHAM Pulse, April 2010, pg2)

A recent research paper by the Duke Clinical Research Institute (Patel MR, et al. Low Diagnostic Yield of Elective Coronary Angiography. N Engl J Med 2010;362:886-95.) should prod every cardiologist to review his or her threshold in the performance of ‘routine’ coronary angiography for the diagnosis of significant coronary artery disease.  

This concept to justify clinical performance processes to help check potentially over-used procedures and testing has now become more and more crucial in the era of evidence-based medical practice and health costs constraints.

More importantly on a practical basis, we are exhorted to contribute more actively towards checking escalating health care cost by becoming more thoughtful and judicious in our clinical decision-making.

Justifiable Diagnostic Screening still Unresolved
In the USA, some USD14.1 billion is spent on imaging diagnostic testing annually by Medicare alone. More and more are now spent on early diagnostic procedures in the hope of detecting and treating potentially lethal coronary artery disease, but which seems to elude the very best of our diagnostic efforts and risk stratifying strategies.

Cardiologists have an unenviable position with regards to the heightened awareness of risks of coronary artery disease, among the general public globally.

Because of the huge success of our diagnostic and therapeutic capabilities, and the very many high profile celebrities surviving or even dying from heart attacks, widespread health promotional education has enlightened the public as never before.
It would be true to say that nearly every one has heard of the dangers of heart attacks and perhaps too all the major risk 
factors. Thus, it is not difficult to envisage that whenever any one person feels some twinges in the chest or suspect that he or she might be suffering a heart ailment, many present themselves to physicians for clarification and testing, and perhaps especially for reassurance that all is well, or otherwise.

Hence, there is a rising demand for health screening testing including exclusion of significant heart disease.

Unfortunately, even as we get more sophisticated, we do know that the diagnostic yield of most health screening tests for significant heart disease is disappointingly low. From simple risk factor assessments and stratification, stress ECG, stress echocardiograms to even calcium scoring to MSCT-angiogram, we are still only finding tiny incremental yields to help us not miss potentially lethal heart disease or sudden death.

Perhaps, this is the result of greater unrealistic expectations from both patients and physicians alike. We have become more enamoured by our abilities to reduce the scourge of heart disease, so much so, that we are continuously looking for the Holy Grail at preventing earlier and earlier unstable plaques, which can trigger sudden loss of life. Some harbour hopes of totally eradicating coronary artery disease itself!

A few years ago, a group of eminent cardiologists in their enthusiasm to advocate earlier detection of heart disease, pushed for a public health program to screen more aggressively for heart disease and unstable plaques, the MDCT was the touted approach then for mass screening. However, this was not universally adopted when clearer views of such a program were scrutinized. The less than consistent detection rates, resolution discrepancies, artifacts, radiation risks of mass screening with CT angiogram has stalled the more widespread use of this modality.

Then, there have been others, (cardiologists, both academic and private sector) who have swung even farther to the right of ‘gold-standardising’ diagnosis with routine coronary angiography, on demand even to detect or to exclude significant coronary stenosis. They persuade their patients that this is the only sure way of not missing anything to do with their heart, except that this is disingenuous: there is no guarantee that a heart attack would not occur in the future!

This approach is clearly unacceptable and when used as a casual screening tool, almost universally regarded as Class III indication, or worse that which may cause harm. Risks of tachyarrhythmias, embolic phenomena, CVAs, renal impairment or even untoward unexpected bleeding, while very low, are not zero. The latest analysis of the ACC National Cardiovascular registry database therefore lends weight to the fact that indiscriminate testing with unnecessary coronary angiography has low yields, which cannot be justified!

The American College of Cardiology National Cardiovascular Data Registry (NCDR) Results:
Of the nearly 2 million coronary angiographies performed in the NCDR database, some 60.3% had significant obstructive CAD (Obstructive coronary artery disease was defined as stenosis of 50% or more of the diameter of the
left main coronary artery or stenosis of 70% or more of the diameter of a major epicardial or branch vessel that was more than 2.0 mm diameter. When sensitivity was broadened to any stenosis of 50% or more for any coronary vessel, this increased diagnostic yield results by some 4%.)

When acute coronary syndromes, cardiogenic shock, proven past CAD, past histories of revascularisation procedures, and other defined indications were excluded, some 397,954 were eligible for analysis. Of these, the yields are as shown in the figure below:

Noninvasive testing (resting electrocardiography, echocardiography, computed tomography [CT], or a stress test) was performed in 83.9% of the patients before invasive angiography, of which 68.6% had a positive test result. Patients with a positive noninvasive test result had higher rate of obstructive coronary artery disease than those who did not, before angiography (41.0% vs. 35.0%, P<0.001); the rate of obstructive CAD among patients with a positive test result was also higher than the rate among those with equivocal or negative test results (41.3%, vs. 27.1% and 28.3%, respectively).

Since the data set included asymptomatic and symptomatic patients, the association between rates of obstructive coronary artery disease and the results of noninvasive tests are presented in Figure 2 according to Framingham risk-score categories (low, intermediate, or high) and symptom categories (no symptoms, atypical symptoms, or angina). The diagnostic yield for obstructive coronary artery disease increased with a higher Framingham risk score, as well as with the presence of angina 
(P<0.001 for both analyses).


Figure 3 below shows the model’s predictive ability when symptom characteristics, i.e. beyond Framingham risk scores alone were analysed. However, stratifying Framingham risk levels, with positive, equivocal or negative noninvasive test was associated with very small incremental yields for presence of obstructive coronary artery disease (C-statistic, 0.764; 95% CI, 0.762 to 0.765), for all three Framingham risk levels.

It appears that less than 4 in 10 among those undergoing invasive coronary angiography (37.6%) had obstructive CAD (i.e., ≥50% stenosis of the left main coronary artery or ≥70% stenosis of a major epicardial vessel). The percentage was similar (41.0%) when the definition of obstructive disease was expanded to include stenosis of 50% or more of any coronary vessel.

Thus, although certain demographic and clinical characteristics could be useful in determining the likelihood that obstructive coronary artery disease would be present, the incremental value of a positive result on a noninvasive test (including any of a broad range of tests such as resting electrocardiography, echocardiography, CT, or stress test) was limited.

This begs the question whether such diagnostic tests should be promoted in a systematic way. Of course, this does not mean that those with clear indications should not be referred for such testing, if not for therapeutic options, then for risk stratification strategies and management.

But, this poses challenges for cardiologists and physicians who should be very clear in discussing with their patients the realistic clinical utility of non-invasive testing and especially for coronary angiography. For those with not much or typical symptoms, then most of these tests may not serve to enlighten either the doctor or the patient as to his or her status of cardiac health!

So, What should Cardiologists Do?
In Malaysia, we do have an unhealthy love affair with all that is new and fashionable, especially technology-driven equipment and techniques. These are touted as must-have amenities bordering on questionable competition for who has the newest, most advanced equipment. There are about 20 ultra-fast multi-detector CT scanners in the Klang valley; and another 15 or so cardiac catheterisation laboratories as well.

Business people in collaboration with physicians, usually fund such huge capital-intensive enterprises, which then demand quick returns on their investments. Thus, there is an unspoken nudge toward greater utilization of such facilities to help justify their purchases. To compound the problem, it is not inconceivable that cardiologists are also venally encouraged to use more of these testing modalities, because they would personally benefit from procedure fees—the sort of asymmetrical moral hazard, which has been decried by many health economists.

In several reports now, a few cardiologists in the USA have been charged and indicted for fraud for performing un-indicated coronary angiography, and even unnecessary angioplasties. Linked hospitals have also been fined huge sums for condoning over-utilisation of such procedures without sufficient oversight or appropriate audit.

With the NCDR data in mind we should now seriously reconsider our penchant for early invasive testing, and resort to better evidence-based medicine to offer our patients the optimum care without fear of under-diagnosing or missing non-critical disease, which are usually not life-threatening (this is not addressed in this analysis). But we do have past precedents, the COURAGE study had shown quite conclusively that when given optimal medical therapy, even significant but stable coronary artery disease can be managed quite well, with no increase in mortality or major adverse complications.

Let’s give more thought as to how we practice cardiovascular medicine and remind ourselves that the best medicine is one that is evidence-based and purely for the patient’s benefit, not ours or our personal financial gain per se.

We have to learn to stay our reflexive tendency to diagnostic or therapeutic procedures which may not improve risk assessment or clinical management for our patients, but which may instead increase their potential harms and incur unnecessary costs.

Unless we rein in our free-for-all approach, the escalation in costs may actually impose external oversight and imposition of audits and cost-constraints for reimbursements, through case-mix or DRG models.

Worse, callous over-utilisation of procedures including coronary angiography may demean the trust and esteem which the public has for the physician, the cardiologist, and impeach our much-vaunted medical professionalism!

1 comment:

Cuddly Bear said...

I am an academic family physician in Sugar Land, Texas. I see patients and teach in a family medicine residence program.

The problem, as I see it, with Patel et al's interpretation of the elective coronary angiography data in the March NEJM article, is that it ignores the 23.2% of patients found to have nonobstructive CAD (20-49% left main or 20-69% other coronary stenosis). These patients are also at high risk for myocardial infarction (and stroke, since they are likely to have concomitant carotid artery disease). Aggressive medical management of their reversible risk factors is advisable to reduce their cardiovascular event risk. If they are like my patients, many of them are reluctant to take statins unless they think they "have to." Finding out that they have even "non-obstructive" coronary artery disease makes many of them more accepting of statin therapy. So detecting those with subcritical CAD can prevent some heart attacks and save some lives. If the non-obstructive CAD cases are added to the obstructive CAD, that makes the diagnostic yield 60.8%. Patel et al's "glass half empty" conclusion is that a little over one-third of the patients had obstructive coronary disease. My "glass half full" conclusion is that almost two-thirds of the patients had clinically significant coronary artery disease.

Michael Crouch, MD, MSPH
Memorial Family Medicine Residency Program