Identifying Early Cardiovascular Disease to Target Candidates for Treatment

Abstract

Most attempts to identify individuals at risk for cardiovascular morbid events have involved screening for risk factors. These traditional risk factors do not identify the underlying atherosclerotic disease nor assess the severity of disease in individual patients. The goal for identifying a marker or markers for early cardiovascular disease that could serve as a surrogate for disease progression and ultimate morbid events is to improve the precision for early detection and treatment. The authors utilize a variety of techniques, which consist of 7 vascular tests (large and small artery elasticity, resting blood pressure and exercise blood pressure response, optic fundus photography, carotid intimal‐media thickness, and microalbuminuria) and 3 cardiac tests (electrocardiography, [N‐terminal pro‐] B‐type natriuretic peptide, and left ventricular ultrasonography). Each test is individually scored, and the total disease score is the sum of all the test scores. A study is ongoing to compare the new disease score vs the classical Framingham risk estimate in the prediction of cardiovascular events.

Atherosclerosis is a devastating disease because it is the most frequent cause of myocardial infarction, stroke, renal failure, peripheral vascular disease, and perhaps even dementia. Thus, the complications of atherosclerosis have a profound impact on quality of life, life expectancy, and health care costs. ¹ Most attempts to identify individuals at risk for cardiovascular (CV) morbid events have involved screening for risk factors. These risk factors have included smoking, blood pressure (BP), cholesterol elevation, obesity, physical inactivity, and other well‐established targets for intervention. They are not disease markers, but rather phenomena statistically associated with disease. ² , ³ , ⁴ Data from epidemiologic studies and intervention trials support the benefit on morbid events of aggressive attempts to modify these risk factors. ⁵ When dealing with a healthy population, however, the efficacy of these interventions may be modest and the number needed to treat to prevent a morbid event is considerable. ⁶ , ⁷

EARLY VASCULAR DISEASE DETECTION

By identifying individuals with evidence of early CV disease (CVD) before the occurrence of symptoms or morbid events, one should be able to identify a population far more likely to progress than the general population who may have no early disease. ⁸ , ⁹ By aggressive intervention in this population, first morbid events may potentially be delayed or prevented and the result should be a healthier, asymptomatic population who can anticipate a normal life expectancy. ¹⁰ This approach may be viewed as a variation of secondary prevention, because it is designed to identify disease before it becomes clinically manifested and to intervene before symptoms occur.

The fact that morbidity and mortality events do not serve as a sensitive or specific guide to disease progression renders surrogate markers an important potential contributor to understanding the natural history of disease and its response to therapeutic intervention. Some potential surrogate markers progress with time; therefore, an alteration in the surrogate may be a slowing of the time‐dependent progression rather than necessarily a normalization of the surrogate. This concept of progression and the trajectory of time‐dependent structural or functional measures as predictors of subsequent events are important in understanding the value of certain surrogate markers. ¹¹ , ¹²

Atherosclerotic disease is usually viewed as the development of lesions in the wall of conduit arteries that lead to obstruction to blood flow and/or clot formation that impede perfusion. The term atherothrombotic disease has recently evolved to clarify the mechanistic understanding that lipid‐containing plaques and thrombotic events go hand in hand and the underlying process is endothelial dysfunction. ¹³ , ¹⁴ , ¹⁵

DIAGNOSTIC TESTS

In considering the ways to identify functional and structural abnormalities of the vasculature and heart, we use a variety of techniques that are complimentary. This allows us to establish an individual's absolute CVD score. ¹⁶ , ¹⁷

Vascular Tests

Large and Small Artery Elasticity. BP is one of the major determinants of CV risk. In clinical practice, 2 specific and arbitrary points of the BP curve, peak systolic and end‐diastolic BP, are used to define CV risk. Traditionally, the BP curve has been considered to contain a steady component, mean BP, and a pulsatile component, the pulse pressure. The growing importance of pulsatile pressure indices paralleled the notion that not only increases in systemic vascular resistance but also increases in arterial stiffness are important in the pathophysiology of hypertension. ¹⁸ Information about the interaction between the left ventricle and the physical impact of the arterial circulation can be derived by the descriptive and quantitative analysis of the arterial pressure pulse waveform. ¹⁹

Although the large conduit arteries are the target for atherosclerotic plaque formation, the endothelial dysfunction, which precedes such plaque development, involves the small arteries as well as the conduit arteries. In the setting of endothelial dysfunction, a reduction in nitric oxide bioactivity will result in a reduction in caliber of the small arteries and an increase in their tone. From the vascular standpoint, the reduction in caliber may lead to an increase in systemic vascular resistance; the alteration in tone alters the oscillations or reflected waves generated in the arterial bed that influence the contour of the arterial pressure waveform. ²⁰ By noninvasively assessing the waveform, one can identify this alteration in the small artery function or structure by an alteration in the diastolic pressure decay. This pulse contour analysis methodology has now been applied to a wide range of patient groups and can be considered as a potential marker for the risk of future CV events. ²¹

Conduit artery disease exists long before symptoms develop or morbid events occur. Aging and atherosclerosis exert their conduit artery effects by thickening the wall as well as eventually inducing luminal plaques. Measurements of arterial stiffness provide useful information regarding the health of the arterial vasculature. Large artery stiffness, as assessed by pulse pressure and pulse wave velocity, is age‐dependent and reflects structural alterations in the conduit arteries that are accelerated by hypertension and atherosclerosis. Methodology is now available to use arterial stiffness as a marker for premature disease and to track changes in stiffness as a guide to progression of disease and the impact of therapy. ²²

Sitting BP. BP is a well‐established risk marker. ²³ An important number of CV events that occur in our society, however, are experienced in individuals whose BP is not above the normal range. The evidence that BP is linearly related to the risk of morbid CV events is remarkably strong. ¹⁸

The relationship between BP and stroke is more pronounced than it is with ischemic heart disease and other vascular events. Because the risk and benefit appear to be linear, the absolute BP level at which treatment should be instituted remains controversial. Recent guidelines that emphasize BPs >120/80 mm Hg as a risk (prehypertension) reflect evolving and differing views. ²⁴ The choice of what phase of the pulsatile pressure to focus on and on what conditions (rest or stress) should exist at the time the measurements are made remain controversial.

The value of BP as a marker for risk and as a target for therapy in large population studies does not address its possible inadequate precision in monitoring individual patients. More precision in methodology and better means of separating high‐risk from low‐risk individuals may be necessary to make BP a more useful tool in clinical practice. Whether the ultimate screening tool will be resting BP, stress‐induced pressure, or some additional measure of vascular health, to augment data from the BP readings will require further study.

Treadmill Exercise BP. During exertion, a rise in cardiac output is buffered by a reduction in systemic vascular resistance that modulates the rise in BP. In the setting of endothelial dysfunction with an increase in vascular tone, the reduction in systemic vascular resistance may be impaired or delayed, thus resulting in an accelerated rise in BP during exertion. This mechanistic possibility has provided the opportunity to monitor the BP rise during a fixed treadmill workload for 3 minutes as a guide to the functional integrity of the CV system. Early data suggest that the rise in BP and its ultimate maximum provide more insight than resting BP alone in identifying early vascular disease. Abnormal BP response to exercise has been related to an increased risk of developing hypertension and also to a higher risk of stroke. ²⁵ , ²⁶ Moreover, exercise‐induced hypertension is associated with decreased CV event‐free survival. ²⁷

Optic Fundus Photography. Visualizing the vasculature of the retina provides the opportunity for a direct assessment of the small arteries. Funduscopic examination provides a window into the small vessels. Changes in the arteriovenous crossings in the retina can reveal the effect of thickening of the arteriolar wall and impact on the associated venule. These changes in arteriovenous crossing can then help to identify the early vascular disease that may eventually lead to morbid events. ²⁸ , ²⁹ New nonmydriatic cameras facilitate collection of digital images that allow rigorous assessment of the arterial/venous crossings and arterial architecture. ³⁰

Measurement of Carotid Intima‐Media Thickness. Considerable data exist on the rate of increase of intimal‐media thickness (IMT) in the carotid artery with age and its abnormality with disease states. ³¹ Early studies confirm that this methodology can be employed in a screening mode and that it has the power to detect disease long before symptoms develop. ³²

Carotid IMT is a direct measure of the status of the vascular wall; abnormalities are not a surrogate but a direct measure of atherosclerotic and arteriosclerotic processes. The degree of carotid disease that appears to be of prognostic value is much subtler, requiring meticulous and detailed measurements of IMT through B‐mode ultrasound. Carotid atherosclerosis has been correlated with risk factors associated with the development of atherosclerosis in any vascular bed. ³³ Prevalence of coronary artery disease, cerebrovascular disease, and peripheral vascular disease increased in parallel with increasing IMT. Accordingly, the finding of a significant association between a quantitative abnormality of the carotid IMT and evidence of established coronary artery disease is reassuring and is concordant with the principle that atherosclerosis is a diffuse disease. Detection in one bed implies a high likelihood of association with atherosclerosis in a different bed. Even more compelling is evidence showing that carotid atheroma is a predictor of vascular events and that it is useful for risk stratification. ³⁴ It is clear that IMT is sex‐and age‐related. The establishment of standards for performance and interpretation of carotid IMT is critical for further utilization of this technique. A normal age‐dependent range for quantitative assessment must be established for geographic, sex, and ethnic groups.

Microalbuminuria. Microalbuminuria has been recognized as a marker for small artery disease in the kidneys that results in leakage of albumin into the urine. This measurement has provided an additional marker for early vascular disease and appears to be sensitive in identifying high‐risk patients who have not yet sustained morbid events. The appearance of trace amounts (microalbuminuria, 30–300 mg/d) and larger amounts (frank proteinuria, >1 g/d) of albumin are associated with an increased risk of renal failure, heart disease, stroke, and CV mortality. ³⁵ , ³⁶ Albumin excretion is best expressed as a function of creatinine or as a clearance. Timed 24‐hour urine collection has been the gold standard for quantifying urinary protein excretion but is limited by poor compliance and a cumbersome collection technique. Modifications of 24‐hour collection to include shorter collection time (12‐ or 4‐hour collection after a standard water load or first morning void) have yielded to the simplicity of measuring a spot protein/creatinine ratio. Ultimately, the spot protein/creatinine ratio provides an approximation of the level of proteinuria. Any standard laboratory will perform this analysis.

Cardiac Tests

Electrocardiography. Electrocardiography (ECG) is still considered a screening tool for arrhythmias, conduction abnormalities, myocardial ischemia, old myocardial infarction, and left ventricular hypertrophy (LVH). The best‐documented ECG‐LVH criteria are Sokolow‐Lyon and Cornell Voltage Duration Product. It has been demonstrated that nonspecific (minor) ST‐segment depression and/or T‐wave abnormalities have a long‐term prognostic impact for coronary heart disease and CVD death in middle‐aged women and men and can be considered markers of heightened coronary heart disease and CVD risk. ³⁷

Left Ventricular Ultrasonography. Cardiac screening is aimed at a different chain of events. Asymptomatic left ventricular dysfunction may exist before the clinical syndrome of heart failure appears. As a risk indicator for future CV events, LVH is strong and independent and second only to age in predictive power. Finally, there is documentation for both ECG‐LVH and echocardiographic LVH that reversal has an independent prognostic value, independent of therapy and BP. ³⁸ BP lowering with all of the available antihypertensive agents, except vasodilators, has resulted in reversal of LVH. That LVH has become a validated surrogate end point for the treatment of hypertension has clinical implications. Many new diagnostic advances, however, may further refine this valuable tool.

(N‐Terminal Pro‐) B‐Type Natriuretic Peptide. The plasma level of this cardiac hormone has emerged as a sensitive and specific guide to the presence of heart failure in symptomatic patients and to left ventricular dysfunction in asymptomatic patients. The concentration is a determinant of adverse outcome in heart failure and appears to correlate with a favorable therapeutic effect on outcome. As such, plasma (N‐terminal pro‐) B‐type natriuretic peptide may ultimately prove to be a reliable surrogate marker for the severity of left ventricular remodeling and perhaps a sensitive and specific marker for the progression of cardiac disease in ischemic and nonischemic forms of cardiomyopathy. ³⁹

EARLY CVD SCORE VS RISK SCORE

We have developed a global model that consists of composite disease markers called the Rasmussen Disease Score, named for the benefactor of the Rasmussen Center for Cardiovascular Disease Prevention. The history, physical examination, and laboratory testing in the center are carried out by a nurse practitioner and a medical technologist. The total duration of the center visit is confined to 2 hours: 1 hour dedicated to extensive history, CV examination, and lifestyle discussion; and 1 hour to the testing procedures. The entire 2‐hour screening takes place in one room, where all the necessary equipment is installed for the different measurements.

A cardiologist oversight includes chart and data review, report generation, and direct patient contact, only when indicated. Screening consists of modifiable disease contributor assessment. Our strategy has been to use a combination of 7 vascular and 3 cardiac tests to better define the presence of early disease. The basis for selecting the 10 tests has been discussed above. This approach requires a scoring system for the biological detection of early disease. The Table summarizes the Rasmussen Disease Score and the scoring of each test. Each of the 10 tests is scored as follows: 0 for normal, 1 for borderline abnormal, and 2 for abnormal. The total score for any individual may therefore range from 0 to 20. ⁸ The additional information from the “risk contributors” assessment is then used to design a management strategy. We have now screened 1500 patients. One‐third of this population has a Rasmussen Disease Score between 0 and 2 (low risk), one‐third between 3 and 5, and one‐third 6 and above, which is considered high risk. Tracking of events is also in process to evaluate this personalized disease score compared with the classical CV risk scores. At present, there is no proof that this type of screening will improve outcome over and above treating known risk factors; however, we are performing a study to compare the new disease score vs the classical Framingham risk estimate in the prediction of long‐term CV events.

Table.

Rasmussen Disease Score With the Scoring of Each Individual Test

Test	Rasmussen Disease Score
	Normal (Score = 0)	Borderline (Score = 1)	Abnormal (Score = 2)
Large artery elasticity	Age‐ and sex‐dependent
Small artery elasticity	Age‐ and sex‐dependent
Resting BP, mm Hg	SBP <130 and DBP <85	SBP 130–139 or DBP 80–89	SBP ≥140 or DBP ≥90
Exercise BP, mm Hg	SBP rise <30 and SBP ≤169	SBP rise 30–39 or SBP 170–179	SBP rise ≥40 or SBP ≥180
Retinal vasculature	A/V ratio >3:5	A/V ratio ≤3:5 or mild A/V crossing	A/V ratio ≤1.2 or A/V nicking
Carotid IMT	Age‐ and sex‐dependent
Microalbuminuria, mg/mmol	≤0.60	0.61–0.99	≥1.00
Electrocardiography	No abnormalities	Nonspecific abnormalities	Diagnostic abnormalities
LV ultrasonography, LV mass index	<120 g/m2	120–129 g/m2	≥130 g/m2
BNP, pg/dL	≤50	50–99	≥100
Abbreviations: A/V, arteriovenous; BNP, B‐type natriuretic peptide; BP, blood pressure; DBP, diastolic BP; IMT, intima‐media thickness; LV, left ventricular; SBP, systolic BP.

COST

The cost of testing in the Rasmussen Center has been reimbursed by private insurers, based on the current procedural terminology codes for individual tests. The reimbursement date will likely vary depending on local reimbursement policies and specific insurance coverage.

CONCLUSIONS

Most attempts to identify individuals at risk for CV morbid events have involved screening for risk factors that are statistically associated with future cardiac and cerebrovascular events. This approach has resulted in several risk factor assessment scales that can identify groups with higher risk but may provide limited information about individual risk. ⁴⁰ Since the risk factors used are not necessarily disease markers, however, this approach does not provide insight as to how the risk factors are impacting the biologic target organs, the vasculature, and the heart. Screening tests, which identify early vascular and cardiac functional and structural abnormalities, may identify abnormalities in asymptomatic individuals without obvious risk factors for CVD. Bringing these techniques to so‐called asymptomatic individuals who have not yet sustained CV events represents the challenge for the 21st century.