Comparison of Perception of Angina Pectoris DuringExercise Testing in African-Americans

Versus CaucasiansDavid Sheffield, PhD, D. Scott Kirby, MD, Paula L. Biles, BA, and

David S. Sheps, MD, MSPH

S ince the introduction of electrocardiographic ex-ercise testing, it has been recognized that patients

can have ST-segment depression without angina pec-toris.1,2 Both the severity of ischemia3,4 and individualdifferences in sensory perception5,6 determine whetherischemia is silent or symptomatic. Pain perception andresponse differences have been shown to exist be-tween cultures and races; African-Americans havegreater sensitivity to experimental and clinical painthan North American Caucasians.7–9 However, nostudy has examined the relation between race andangina perception. Accordingly, in this study we in-vestigated race differences in reports of angina duringexercise testing in patients with a positive result.

• • •We reviewed all exercise treadmill tests performed

at University of North Carolina hospitals during 1990to 1994. Of the 4,723 reviewed, 1,144 patients withpositive tests (24%), defined as exercise-induced hor-izontal or downsloping ST-segment depression of$1mm at 0.08 second after the J point, were selected foranalyses. All positive tests were confirmed by thesame experienced cardiologist. Of the 1,144 patientswith positive tests, 1,000 with the following condi-tions were excluded from analyses: (1) conditions thatcould affect anginal pain perception (diabetes melli-tus, post–coronary bypass surgery); (2) exercise pro-tocol other than standard Bruce protocol; (3) restingelectrocardiographic abnormalities that could influ-ence test interpretation (left ventricular hypertrophy,Wolff-Parkinson-White syndrome, left bundle branchblock, or remarkable intraventricular conduction de-fect); (4) electrocardiographic changes with posture orhyperventilation; (5) taking digitalis or antianginalmedication includingb blockers, calcium channelblockers, or long-acting nitrates; (6) age#35; (7)normal or nonsignificant coronary artery disease(,50% diameter narrowing) from coronary arteriog-raphy; and (8) subsequent nuclear imaging study notsuggestive of flow-limiting disease. For patients whohad$2 positive tests, we selected only the first pos-itive test for analysis; data from 142 patients wereused in our analyses.

Each patient performed a treadmill exercise test

using a symptom-limited standard Bruce protocol anda Marquette system. The baseline of ST-segment anal-ysis was established as the level of ST segment ob-served in the standing position before the start ofexercise. Leads aVF, V3, and V5 were continuouslymonitored. Twelve-lead electrocardiograms were re-corded before exercise in the supine, standing, andposthyperventilation conditions, at 1-minute intervalsduring exercise and until at least 5 minutes into re-covery phase or return to baseline. Blood pressurerecorded by cuff sphygmomanometer was taken at restbefore exercise, at 2 minutes into each stage of theprotocol until at least 5 minutes into the recoveryphase, or return to baseline level. In addition, 12-leadelectrocardiograms were monitored and blood pres-sure measured at the time of onset of angina and at thetime of onset of positive test, defined as$1-mmST-segment depression at 0.08 second after the J pointfor $3 mm, $3 consecutive ventricular prematurecomplexes, or decrease in systolic blood pressure by$10 mm Hg. Patients were instructed to inform thesupervising physician immediately of the onset andresolution of chest pain. In addition to the demo-graphic and clinical information, the following exer-cise variables were recorded in each patient: (1) heartrate, blood pressure, and rate-pressure product at rest,onset of 1-mm ST-segment depression, onset of chestpain, and maximal exercise; (2) time at onset of 1-mmST-segment depression, at onset of chest pain, andtotal exercise time; (3) maximal ST-segment depres-sion and electrocardiographic leads in which the ST-segment depression was present; and (4) the presenceor absence of typical chest pain.

Continuous variables were described with mean6SE, and categorical variables were described withfrequencies and percentages. Differences betweencontinuous data were performed by Student’st test forpaired and unpaired data, as appropriate. Comparisonsbetween proportions were made with the chi-squaretest. A p value,0.05 was considered significant.

Of the 1,144 patients with positive exercise tests,142 met the criteria for analyses. There were 124Caucasians and 18 African-Americans (mean age 59years [range 36 to 84]). Mean total duration of exer-cise was 6.86 0.2 minutes. Patients developed$1-mm ST-segment depression at the average of4.8 6 0.2 minutes into exercise. Average heart rate atthe onset of 1-mm ST-segment depression was 13462 beats/min. Exercise-induced ischemia was accom-panied by angina in 43 patients (30%).

African-Americans (9 [50%] had angina) weremore likely to have angina during exercise testing than

From the Department of Internal Medicine, East Tennessee State Uni-versity, Johnson City, Tennessee; and Division of Cardiology, Univer-sity of North Carolina at Chapel Hill, Chapel Hill, North Carolina. Thisstudy was supported in part by Grants 1-R29-HL-56825 and 2-R01-HL-47477 from the National Heart, Lung, and Blood Institute, Be-thesda, Maryland. Dr. Sheffield’s address is: Division of Cardiology, Box70622, Department of Internal Medicine, East Tennessee State Univer-sity, Johnson City, Tennessee 37614-0622. Manuscript received Febru-ary 1, 1998; revised manuscript received and accepted July 28, 1998.

106 ©1999 by Excerpta Medica, Inc. 0002-9149/99/$–see front matterAll rights reserved. PII S0002-9149(98)00790-5

Caucasians (34 [27%] had angina, p5 0.05; see TableI). In addition, in patients with angina during exercisetesting, African-Americans had a somewhat shortertime (2116 31 seconds) to angina than Caucasians(3056 25 seconds, p5 0.08). Table I lists the clinicaland exercise characteristics of patients with and with-out angina during exercise testing. Patients with an-gina were more likely to be smokers and had lowersystolic blood pressure at rest and at the onset of1-mm ST-segment depression than those with silentischemia. In addition, patients with angina were morelikely to be referred for catheterization or nuclearstudy. However, there were no differences in diseaseseverity as indexed by the number of occluded vesselsand time to and duration of 1-mm ST-segment depres-sion. African-Americans were more likely to bewomen (50% vs 18%, p5 0.002) and had a somewhatshorter time to ST-segment depression than Cauca-sians (2296 29 vs 2986 13 seconds, respectively,p 5 0.05). Time to angina was also related to time toST-segment depression (r5 0.46, p5 0.002) and age(r 5 20.28. p5 0.07).

Given these differences, the relation between raceand the expression of ischemia was examined afteradjusting for time to ST depression, systolic bloodpressure at rest, smoking status, and gender usinglogistic regression. Race remained a predictor of an-gina after controlling for these variables (Wald53.46, p5 0.06). Regression analysis revealed that racewas still related to the timing of angina after control-ling for time to ST-segment depression and age (p50.07). The same pattern of findings were found inanalyses of subsamples that: (1) included only the 90

patients with documented disease (asindexed by positive catheterization,positive nuclear study, or history ofmyocardial infarction; p5 0.05 forfrequency of angina, and p5 0.10for time to angina); and (2) includedonly the 60 patients with positivecatheterization results (p5 0.06 forfrequency of angina, and p5 0.20for time to angina).

• • •Our results showed that African-

Americans reported anginal pain attwice the rate of Caucasians. In ad-dition, African-Americans had ashorter time to angina than Cauca-sians. These relations were not al-tered after controlling for disease se-verity, as indexed by time to ST de-pression. Because systolic bloodpressure at rest is related to the pres-ence of chest pain,10 we also statisti-cally controlled for its effects. Racewas still related to angina perceptionafter adjusting for blood pressure.The same pattern of results werefound in a subsample that only in-cluded patients with positive cathe-terization results.

The concept of racial differences in pain perceptionhas been of clinical interest for many years and stud-ied extensively since 1960 using various painful stim-uli and measurement techniques.6 However, few painstudies of race differences have used large, ethnicallydiverse populations and incorporated consistent caus-ative stimuli and measurement techniques6,9 making itdifficult to generalize their findings. Three laboratorystudies found that Caucasians had increased pain tol-erance to experimental stimuli than African-Ameri-cans.7,8,11 Thus, our clinical data are congruent withthe findings of experimental studies.

Proposed mechanisms for these racial pain re-sponse differences encompass diverse areas includingunderlying physiologic responses, ethnocultural dif-ferences, the subject’s psychological state, socioeco-nomic differences, and experimenter bias. Attentionhas focused on psychosocial and cultural factors ratherthan physiologic differences between races.6 Onephysiologic factor that has been related to pain per-ception is blood pressure.10 However, although bloodpressure differences between races have been noted,blood pressure did not differ by race in our study, andtherefore could not explain the race differences inangina perception we observed. Thus, other mecha-nisms must cause these differences. With respect topsychological factors, both depressed mood and anx-iety have been shown to increase pain perceptionduring exercise testing.12–14 Given that the race dif-ferences we observed are reliable, assessing their cul-tural, psychosocial, and physiological determinantswould aid our understanding of individual patients’angina perception.

TABLE I Demographic, Clinical, and Exercise Characteristics of Patients With andWithout Angina

Myocardial Ischemia

p ValuePainful

(n 5 43)Silent

(n 5 99)

African-Americans 9 (21%) 9 (9%) 0.05Age (yr) 56 6 2 60 6 1 0.12Men 35 (81%) 76 (76%) 0.54Current smokers 15 (35%) 16 (16%) 0.01Systemic hypertension (by history) 14 (33%) 28 (28%) 0.61Myocardial infarction (by history) 6 (14%) 15 (15%) 0.85Underwent nuclear study 32 (74%) 53 (53%) 0.02Underwent catheterization 28 (65%) 32 (32%) 0.0003Number of coronary arteries narrowed

.50% in diameter1 8 (29%) 10 (31%)2 10 (36%) 6 (19%)3 10 (36%) 16 (50%)

Heart rate at rest (beats/min) 77 6 2 79 6 1 0.52Systolic BP at rest (mm Hg) 128 6 3 137 6 2 0.03Diastolic BP at rest (mm Hg) 81 6 2 83 6 1 0.24Rate-pressure product at rest

(beats/min 3 mm Hg)9,917 6 379 10,772 6 258 0.07

Time to 1-mm ST depression (s) 276 6 20 295 6 14 0.47Duration of ST depression (s) 381 6 40 399 6 26 0.72Maximal ST depression (mm) 1.3 6 0.1 1.3 6 0.1 0.82Number of leads with ST depression 4.0 6 0.3 4.0 6 0.2 0.85Systolic BP at 1-mm ST depression (mm Hg) 160 6 4 171 6 3 0.04

BP 5 blood pressure.

BRIEF REPORTS 107

Angina pectoris has been defined as a discomfort inthe chest and/or adjacent area associated with myo-cardial ischemia.15 How physicians discriminate angi-nal pain from nonanginal pain is highly complex andrelies on the patient’s interpretation and communica-tion of symptoms, and physician’s calculation of theprobability that symptoms are of cardiac origin. Fewknown predictors have been determined; most areknown cardiac risk factors. It is possible that race mayalso increase the probability of correct interpretationof exercise-induced angina.16

A limitation of our study is that not all patients haddocumented CAD; however, subgroup analyses ofpatients with significant disease documented by an-giography yielded similar findings. In addition, wewere unable to determine whether race increased theprobability of correct interpretation of exercise-in-duced angina because we did not have a control groupof subjects without CAD. Finally, like most studies ofrace differences, we examined differences betweenCaucasians and African-Americans; it is impossible togeneralize our findings to other races.

In conclusion, we found that blacks reportedanginal pain during exercise at nearly twice therate of whites, and had a significantly shorter timeto angina.

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