Comparison of the Prevalence of First-Degree: DISCUSSION

AV block

An urban hospital setting, the prevalence of first-degree AV block is slightly less in African-American patients compared with Caucasian patients. The greatest contrast of the prevalence of first-degree AV block between the two ethnic groups occurs in the 10th decade of life when the prevalence of first-degree AV block rises to a level of 23.3% (n=10 of 43) in African-American patients compared with only 12.2% (n=22 of 181) in Caucasian patients in the same age group; p=0.06. The cause of the reduced prevalence of first-degree AV block in Caucasian patients in the 10th decade of life is not known. Although the sample size is relatively small for analysis, and the statistical relationship approaches—but does not achieve—traditional criteria of significance, one can speculate that the presence of various disease states involving the AV node could lead to complete AV block, death, or the implantation of an electronic pacemaker. Such a series of events would result in a decreased prevalence of first-degree AV block in Caucasian patients in the 10th decade of life. A similar observation was reported in an earlier study of intraventricular block in which there was a dramatic reduction in the prevalence of left ventricular conduction block in both ethnic groups in the 10th decade of life. This suggested failure of left ventricular conduction with advancing age due to increasing sclerosis of the left ventricular conduction system.

By way of contrast, the greater prevalence of first-degree AV block in African-American patients in the 10th decade of life suggests increasing impairment but greater durability of the AV conduction system in African-American patients compared with Caucasian patients. silagra tablets

First-degree AV block was more common in males at 7.6%, compared with females at 6.5%, in both ethnic groups. Although the relationship was not statistically significant, first-degree AV block was most common in Caucasian males at 7.9% (n=45 of 570) and was least common in Caucasian females at 6.2% (n=39 of 631); p=0.25; and in African-American females at 6.8% (n=37 of 542); p=0.50. In an earlier study, intraventricular block was most prevalent in Caucasian males at 16.8% and was least prevalent in African-American females at 6.5%. Thus, by combining the findings of both studies, Caucasian males have the greatest prevalence of conduction system disease and African-American females have the least prevalence of conduction system disease.

Table 2. Population Surveys of First-Degree Atrioventricular Block by Age and Race

Age Groups (Years)

40-64

45-64

35-74

50-6?

Totals

Number of subjects in age group

287*

2,686#

993*

1,504+

5,470

Race: Caucasian/African-American

143/144

2,193/493

584/409

1,056/448

3,976/1,494

Number of Caucasian subjectswith first-degree atrioventricular block

4

34

1

40

79

Percent

2.0

Number of African-American subjects with first-degree atrioventricular block

13

20

4

23

60

Percent

4.0

Source:

Strogatz5

Vitelli6

Sutherland7

Riley8

* all males; #698 Caucasian males, 1,495 Caucasian females, 116 African-American males, 377 African-American females; + 423 Caucasian males, 633 Caucasian females, 180 African-American males, 268 African-American females

In studies of pooled data of population-based surveys, the prevalence of first-degree AV block is statistically significantly higher in African-American subjects compared with Caucasian subjects. In Table 2, the prevalence of first-degree AV block in African Americans is 4% (n=60 of 1494) subjects compared with 2% (n=79 of 3976) Caucasian subjects; p= 0.00002. In a large select group of healthy U.S. Air Force male flying personnel, 0.6% of whom were African-American subjects, the prevalence of first-degree AV block is low compared with both hospital patients and with subjects of other population-based surveys. In these largely Caucasian subjects, ages 17-54 years, first-degree AV block occurred in 0.52% (n=350 of 67,375) subjects. In contrast the prevalence of first-degree AV block in African-American subjects in this study, ages 21-26 years, was 1.7% (n=7 of 409) subjects. The prevalence of first-degree AV block in both ethnic groups is greater in the present study of urban hospital patients at 7.0% (n=148 of 2,123) compared with the prevalence of first-degree AV block in pooled data of population-based surveys at 2.5% (n=139 of 5,470). This difference is expected because most patients attending an urban hospital are ill, whereas the majority of subjects in population-based surveys are not ill. In summary, the prevalence of first-degree AV block varies in different groups:

1. Urban hospital group 7.0%;

2. Population-based surveys 2.5%;

3. Healthy U.S. Air Force African-American subjects 1.7%;

4. Healthy U.S. Air Force Caucasian subjects.. 0.52%.

The cause of a prolonged PR interval in patients is often obscure. It may be due to various drugs or disease states which slow AV conduction, but in population-based surveys of mostly healthy subjects the cause of first-degree AV block in both ethnic groups presumably is due to increased vagal tone. In a study of subjects with first-degree AV block, the PR interval was reduced to 0.20 s or less in 88% (n=83 of 94) subjects who had been given intravenous atropine. The combined effects of standing and of exercise in the same group demonstrated that the PR interval was shortened to 0.20 s or less in 89% (n=84 of 94) subjects. These findings suggested that first-degree AV block in these subjects was the result of increased vagal tone. In a study of 289 healthy male professional football players, ages 21-35 years, weight lifting one- to three hours per day was an integral part of training for each player. African-American athletes comprised 34% (n=97) players of the group. Sinus bradycardia at 60 bpm or less was present in 77% (n=223) players of the group, and first-degree AV block was present in 9% (n=26) players. With exercise, the PR interval shortened to less that 0.20 s in every instance. This suggested that increased vagal tone in this group was responsible for the sinus bradycardia and for the associated AV conduction delay.
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The frequency of pacemaker placement was more than twice as great in Caucasian patients compared with African-American patients, presumably because of better intraventricular conduction and more-durable AV conduction demonstrated in an earlier study and in the present study, respectively, in African-American patients compared with Caucasian patients.

SUMMARY

1. In an urban hospital setting, beginning at age 50 years in both ethnic groups, the prevalence of first-degree AV block gradually increases with advancing age, peaking at 23.3% in African-American patients in the 10th decade of life and at 14.6% in Caucasian patients in the ninth decade of life;

2. In Caucasian patients, there is a dramatic decline in the prevalence of first-degree AV block in the 10th decade of life, suggesting increased failure of the AV conduction system in this age group;

3. The higher prevalence of first-degree AV block in African-American patients in the 10th decade of life suggests increasing impairment but greater durability of the AV conduction system compared with Caucasian patients;

4. The prevalence of first-degree AV block is greater in African-American patients compared withCaucasian patients in all age groups in the study except for those patients in the eighth decade of life;

5. First-degree AV block is most prevalent in Caucasian males at 7.9% and least prevalent in Caucasian females at 6.2% and in African-American females at 6.8%.

6. In population-based surveys, first-degree AV block is more prevalent in African-American subjects compared with Caucasian subjects.
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Category: Main

Tags: AV block, AV conduction, electrocardiograms, pacemakers

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