A Synopsis from the Screening for Heart Attack Prevention and Education (SHAPE) Task Force Report

Morteza Naghavi, M.D.

Correspondence:

Morteza Naghavi, M.D.
The Society for Heart Attack Prevention and Eradication (SHAPE)
8275 El Rio, No. 100
Houston, TX 77054
Tel: 713-529-4484
Fax: 713-529-4494
Email: mn@shapesociety.org
URL: www.shapesociety.org
 
Herz. 2007 Jul;32(5):356-361.

Abstract:

Traditional guidelines for prevention of atherosclerotic cardiovascular disease (ACVD) fail to identify very-high-risk individuals (the vulnerable patient) who have extensive atherosclerotic plaques in coronary and other arteries thereby at risk for a near future adverse event. They solely rely on screening for traditional risk factors of atherosclerosis (e.g., cholesterol, blood pressure, smoking, etc.) and do not treat differently those with and without extensive atherosclerotic plaques who have a similar risk factor profile (e.g., Framingham Risk Score). Recent studies have consistently shown that individuals with extensive plaque burden regardless of their risk factor profile are very high risk. Traditional risk factor-based guidelines clearly miss to identify the vulnerable patient whose risk factor profile is normal or borderline (i.e., low- or intermediate-risk categories). Often individuals with similar risk factor profiles have different levels of coronary plaque burden and are on different trajectories for a future cardiovascular event. Risk factors of atherosclerosis are at best predictors of ACVD but cannot identify who has or does not have the disease. While such an approach was the best available method in the 70s and 80s, we now have new noninvasive tools capable of detecting atherosclerosis itself. The existing traditional guidelines for primary prevention of ACVD need to be updated to save the vulnerable patient. To address this problem, the Association for Eradication of Heart Attack, a grassroots organization founded by a group of cardiovascular physicians and researchers, has proposed the SHAPE (Screening for Heart Attack Prevention and Education) guideline based on consensus among an international group of distinguished cardiovascular experts. The SHAPE guideline aims to complement existing guidelines in preventive cardiology and address the detection and treatment of the vulnerable patient. The SHAPE Task Force has thoroughly reviewed available evidence including recent studies and recommended that all asymptomatic men 45-75 years and women 55-75 years (except for a small group < 5% with a very low risk factor profile) must undergo noninvasive screening to detect and measure the amount of hidden atherosclerotic plaques in their coronary or carotid arteries. The higher the amount of plaques the more intensive treatment is recommended. The SHAPE Task Force urges health-care policy makers to update existing national guidelines for primary prevention of atherosclerotic cardiovascular disease.

Current Guidelines in Primary Prevention

The current guidelines in primary prevention recommend initial risk assessment and then risk classification with stratification based on risk factors (eg, the Framingham Risk Score in the United States and the SCORE in Europe), followed by risk reducing goal-directed therapy when necessary (1-4). Although this approach may identify persons at very low or very high risk of a heart attack or stroke within the next 10 years, the majority of the population belongs to an intermediate risk group in which the predictive power of risk factors is low. Most heart attacks occur in this group (high population attributable risk). Consequently, many individuals at risk are likely not to be properly identified and, thus, not treated to more appropriate "individualized" goals, whereas others are misclassified as being at high risk and unnecessarily treated with a pharmacologic therapy, perhaps for the rest of their lives. (5) This strategy is not cost-effective, and, more importantly, it is not good medicine.

The serious limitations of current guidelines are recognized by the American Heart Association (AHA), the National Cholesterol Education Program (NCEP) expert panel, and by the European Third Joint Task Force (1-3). Therefore, use of noninvasive screening tests that identify abnormal arterial structure and function for risk prediction in a given individual can be an option for advanced risk assessment in appropriately selected persons, particularly in those with multiple risk factors who are judged to be at intermediate (~indeterminate) risk (1-3). Such tests could include carotid intima-media thickness (IMT) measured by ultrasound, coronary artery calcification determined by computed tomography (CT), endothelial vasomotor dysfunction evaluated by ultrasound, ankle/brachial blood pressure ratio (ABI), and magnetic resonance imaging (MRI) techniques (1-3).

The Time Has Come

The time has come to reconsider our traditional, relatively imprecise approach to individual risk assessment in primary prevention, and in this report we propose a formal strategy for assessment of risk of clinical cardiovascular disease that is largely based on non-invasive screening for the disease itself (subclinical atherosclerosis) rather than its risk factors. The purpose is to identify those who are susceptible to atherosclerosis and its thrombotic and arrhythmogenic complications (vulnerable patients) and initiate appropriate care to prevent heart attack, and to avoid treatment of those who don't need it.

New Paradigm for the Prevention of Heart Attack

In Search of the Vulnerable Patient

Parts I and II of this consensus statement elaborated on new discoveries in the field of atherosclerosis that led to the concept of the vulnerable patient (6-7). This focus on the identification and aggressive treatment of the previously unrecognized very-high-risk population neglected the majority of the population who are not in the very-high-risk category. To rectify this major omission, the SHAPE report introduces a new paradigm to stratify the entire U.S. population at risk, and to tailor recommendations accordingly. As shown in Figure 1. A comprehensive assessment of vulnerability to a new future cardiovascular event requires evaluation of vulnerable (rupture prone or high risk) plaque, vulnerable (thrombogenic) blood, and vulnerable (electrically unstable or arrhythmogenic) myocardium. Although detection of vulnerability in the blood and myocardium are important, the plaque component is the most essential element of coronary risk. Without plaque, the risk from blood and myocardium are very low. Therefore the first step in screening for prevention of coronary events should be focused on screening for the plaque component.

Figure 1. A comprehensive assessment of vulnerability to a new future cardiovascular event requires evaluation of vulnerable (rupture prone or high risk) plaque, vulnerable (thrombogenic) blood, and vulnerable (electrically unstable or arrhythmogenic) myocardium. 

Almost all vulnerable individuals have detectable subclinical atherosclerosis, and we now possess the tools to identify it with sufficient predictive power. It is therefore proposed that all apparently healthy men 45-75 years of age, and women 55-75 years of age, with no known CHD and who are considered not to be at very-low-risk (footnoted under Figure 4) -  undergo screening for atherosclerosis. Of the 61,163,000 US population in the SHAPE age range, 3,951,000 have known CHD. The size of the very-low-risk population is difficult to ascertain but is probably around 5-10% based on data from large US cohort studies (8). This population, and those who have already underogone CACS or CIMT assessment, are excluded from the SHAPE eligible population. Since an exact number is not available, 50 million has been chosen as the approximate number who will require SHAPE evaluation. Based on a 50% compliance rate for SHAPE screening over 10 years, and a 5-year re-examination cycle, the number of people required to annual screening after a decade will decrease to 5-6 million per year.

An estimated 875,000 Americans annually experience a first heart attack of which 175,000 are silent heart attacks (9). Since approximately 500,000 of the total will occur in the 50 million SHAPE eligible population (the peak of the pyramid in Figure 1), a screening ratio of 1/100 (500,000/50,000,000) is anticipated. Almost all of the events will occur in the ~50% of the eligible population who have a positive atherosclerosis test. They, therefore, have ~2% annual risk, consistent with the high-risk classification used in the existing US guidelines. However, according to the SHAPE classification in those with positive tests, the annual risk escalates as the burden of atherosclerosis increases, as demonstrated in Figure 2. Those with the highest burden of atherosclerosis are the most vulnerable patients. A major advantage of the SHAPE guideline over the existing guidelines is that in the existing guidelines the low-risk and intermediate-risk population account for the majority of heart attacks, and only less than 20% of the total number of the events results from the high-risk population, whereas in the SHAPE guideline, the majority of heart attacks happens in the high risk population.

Criteria for Recommended Screening Tests
Several factors are used in selecting individual tests as part of a screening program. These factors include 1) the abundance of evidence for the predictive value of the test in the recommended population over and above that available from standard office-based risk assessment tools (incremental value), 2) availability, 3) reproducibility, 4) complementary value with respect to the concept of the vulnerable patient, and/or 5) cost-effectiveness relative to the status quo.

Figure 3 illustrates the array of available diagnostic tests, including traditional risk factor based and tests that more directly evaluate the presence or effect of atherosclerosis.

The following atherosclerosis screening methods were selected as those that currently best fulfill the above criteria:

• Coronary artery calcium (CAC) determined by CT
• Carotid intima-media thickness (CIMT) and plaque determined by ultrasonography

The evidence behind this selection and the suggested threshold values in the 1st SHAPE Guideline have been published previously (9) and can be found at www.aeha.org.

The 1st SHAPE Guideline

In contrast to the existing traditional risk factor based guidelines, this new strategy is primarily based on noninvasive screening for subclinical atherosclerosis using two well-established noninvasive imaging modalities - CT for measurement of CACS and B mode ultrasound for measurement of CIMT and carotid plaque. This strategy is driven by the data-supported principle that the major determinant of risk for atherosclerotic CVD in asymptomatic adults is the presence of the underlying disease itself, i.e, subclinical atherosclerosis. Early detection of atherosclerosis will permit more widespread and effective prevention strategies to be implemented through accurate risk stratification and tailoring the intensity of therapy to the underlying CHD risk in a cost-effective manner.

The screening strategy for risk assessment and the associated treatment algorithm of the 1st SHAPE Guideline are summarized in Figure 4 and reported previously in details (9)

Figure 4.  The SHAPE Guideline Flow Chart.

Compliance with Treatment
Despite significant and consistent data on the benefits of lipid-lowering agents to reduce cardiovascular events, adherence and utilization of these agents remains low. It is important, therefore, that a recent study demonstrated that statin compliance increased from 44% over 3 years to over 90% in those with baseline calcium scores in the top 75th percentile for age and gender (p<0.001) (10). In multivariable analysis, after adjusting for cardiovascular risk factors, age and gender, higher baseline CAC scores were strongly associated with adherence to statin therapy. Thus, in addition to risk stratification, actually seeing their coronary artery can improve patients compliance to treatments such as lipid-lowering therapy.

The ultimate strategy is a multi-step strategy directed towards the different levels of primary prevention (i.e. primary prevention of risk factors in the entire population, primary treatment of risk factors in a smaller at-risk population, primary prevention of events in further smaller pre-symptomatic population, etc). Implementing such strategies can be visualized in a pyramid approach with the primary prevention of risk factors on the bottom and the primary prevention of events in the pre-symptomatic population on the top (Fig 5)

Conclusion:
Recent discoveries have created major paradigm shifts in our understanding of the underlying mechanisms involved in the formation of atherosclerotic plaques and the sequence of events that result in heart attack and stroke. These scientific discoveries, along with new diagnostic and therapeutic developments, have opened the way to unprecedented opportunities, including detection and treatment of the vulnerable patient which is the focus of the SHAPE Guidelines. We urge healthcare policy makers to revise existing national guidelines in light of the SHAPE Task Force report.

Acknowledgement:
The author acknowledges and appreciates the contribution of the SHAPE Task Force. Special thanks to Erling Falk, M.D., Ph.D., Mathew Budoff, M.D., Harvey Hecht, M.D., and PK Shah, M.D.

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