Prevalence of intraventricular block in the general population: The Framingham Study

PROGRESS IN CARDIOLOGY

Prevalence of intraventricular block in the general population: The Framingham Study Bernard E. Kreger, MD, MPH, William B. Kannel, MD, MPH.

Keaven M. Anderson, PhD, and Boston and Framingham, Mass.

A basic halhnark of disturbed intraventricular conduction is prolongation of the ECG QRS interval. Referred to as intraventricular block, this entity appears to some degree not uncommonly in routinely obtained ECGs. Most of what we know about the prevalence and clinical significance of intraventricular block rests on studies‘of various types of patients and selected healthy groups such as active-duty military men. Data based on general population samples are scarce, and the natural history of a prolonged ECG QRS interval remains obscure. As a first step in clarification, we therefore report the distribution of QRS interval among participants in the Framingham study, along with clinical cardiovascular antecedents and concurrent observations. METHODOLOGY

The Framingham study began in 1948 with the drawing of a two-thirds random sample of the 30- to 59-year-old population of the town of Framingham, Massachusetts. Sampling techniques and study design have been fully described elsewhere.’ A total of 5209 men and women, 5127 of them free of coronary heart disease, ultimately entered the study and returned biennially after the initial examination in 1948 through 1951. Of this cohort, 3261 survivors, then aged 52 to 83 years, came for their twelfth biennial examination between 1970 and 1973. At about the same time as cohort examination 12, the first examination of the Framirigham offspring study took place; previous papers have detailed the constitution of this group of 5135 persons.2 This report describes findings in the combined populaFrom the Section of Preventive Medicine and Epidemiology, Evans Department of Clinical Research and Preventive Medicine, University Hospital, Boston University Medical Center, and the Framingham Heart Study. Supported by Contracts No. NIH-NOl-HV-92922 and NIH-NOI-HV52971 and the Evans Department of Clinical Research, Boston, Mass. Received for publication Nov. 7,1988; accepted Dec. 12, 1988. Reprint requests: Bernard E. Kreger, MD, Section of Preventive Medicine and Epidemiology, 720 Harrison Ave., Suite 1105, Boston, MA 02118.

tion of cohort examination 12 and offspring examination 1. The total group of 8396 persons included 3867 men (mean age = 46, range 11 to 83) and 4529 women (mean age = 47, range 5 to 83). Standard Framingham study medical histories, physical examinations, measurements, and. tests were done according to protocol, including routine 12-lead ECGs obtained with single-channel heat stylus machines running at .25 mm/set. The individual examining physicians measured rates and intervals from ECG standard lead II. Diagnosis of various cardiovascular end points was made according to established criteria reported elsewhere.’ Definitions of intraventricular block used for this analysis have been in common use at Framingham and are generally accepted (Table I).3 The few patients with Wolff-Parkinson-White syndrome and those with pacemakers were omitted. Once we evaluated QRS interval distribution by age, sex, and intraventricular block pattern, logistic regression with multiple ordinal outcomes was then used to detect factors associated with prevalence of QRS interval prolongation.’ For this purpose, QRS interval, the dependent variable, was stratified into three categories: no intraventricular block (SO.09 second), incomplete intraventricular block (0.10 to 0.11 second), and complete intraventricular block 00.11 second). Age and sex differences were adjusted for, with the use of the logistic model. The independent variables examined consisted of a variety of clinical expressions of cardiac and vascular disease diagnosed up to the time of the QRS measurement (angina pectorig coronary insufficiency, myocardial infarction, congestive heart failure, hypertension, stroke, transient ischemic attacks), several concurrent ECG findings (myocardial infarction, left ventricular hypertrophy, ventricular and supraventricular premature beats, atrioventricular block, atrial fibrillation), treatment with digitalis and/or quinidine, and a few risk factors for cardiovascular disease and measurements other than ECGs (serum cholesterol, diabetes mellitus, hemato903

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25--

20--

PERCENT

15--

0 .lO-.ll

40-49 50-59 AGE-GROUP Fig.

Table

60-69

SEC

70+

1. Association of agewith duration of prolonged QRS interval in men.

I. Definitions

Completeintraventricularblock:QRS> 0.12 second Incompleteintraventricularblock:QRS= 0.10 - 0.11 second Left bundle branch block pattern 1. Slurred R wave in left precordial leads or lead I, with delayed intrinsicoid deflection 2. Absence of septal Q waves in left precordial leads 3. Small or absent R waves in leads V, and V, Right bundle branch block pattern 1. R-R’, R-r’, or r-R’ complex in lead V, 2. Broad S wave in left precordial leads or standard lead I

Indeterminatebundlebranchblockpattern Neither left bundle branch block nor right bundle branch block, or components of each

crit level, cigarette smoking, forced vital capacity, obesity as measured by body mass index). Definitions of these variables adhere to the Framingham study approach, i>ublished elsewhere in detail.’ Finally, to assess the relative impact of the several items associated with QRS interval prolongation, we performed multivariate logistic analysis, separately for those with coronary heart disease already manifest at the time of QRS interval measurement and for those with neither coronary heart disease by Frainingham criteria nor congestive heart failure. This separation -was made to keep from the pool of subjects without coronary heart disease those who might have congestive failure as the sole sign of coronary disease.

OBSERVATIONS

Almost three quarters of both sexes have a QRS interval of 0.08 second (Table II). Sex differences are apparent in the tails of the distributions, with more women than men having shorter QRS intervals than the modal value and more men than women having prolongations; however, the ranges of QRS intervals were almost identical. Focusing next on QRS intervals longer than 0.08 second reveals some age trends (Figs. 1 and 2). Intervals of at least 0.12 second (usually designated as complete intraventricular block), seldom seen in men younger than age 50, reach a prevalence of almost 11% in the eighth and ninth decades. The same long intervals, even more rare in younger women, occur in almost 5% of the oldest ones. The age effect appears less striking for less extreme prolongations; again, their prevalence in women reaches only about half that in men. Fig. 3 shows the proportion of intraventricular blocks called left, indeterminate, and right, for complete block, by age-group, and Fig. 4 displays the same information for ,incomplete block. By logistic regression, after adjustment for sex, the proportion of complete intraventricular blocks having a right pattern decreases with advancing age (p < 0.05). The same trend appears for each sex analyzed separately, but it is less conclusive (p > 0.05). In those with incomfilete block, in both sexes, there is a predominance of the right pattern

Volume

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Number

4

Intraventricular

16

block prevalence,

Framingham

905

T

14

12 10 ! PERCENT

0 .lO-.ll

8--

SEC

6-4-2-O+

Fig.

again in the

<30

’ 30-39

* 40-49 ’ 50-59 AGE-GROUP

’ 60-69

2. Association of age with duration of prolonged QRS interval in women.

young, which falls gradually with increasing age, and the prevalance of indeterminate pattern rises and clearly predominates after middle age (p < 0.05). For subjects with coronary heart disease, the ratio of complete to incomplete intraventricular block is 8:lO for both left and right patterns. This ratio was obtained for both sexes, and there is no statistically significant difference between left and right. For subjects without coronary heart disease, we observed the same prominence of both left and right patterns in complete versus incomplete block, again with no difference between men and women. However, in this group, the proportion .of complete left bundle branch blocks (77% of all left patterns) significantly exceeds that of complete right bundle branch blocks (58% of all right patterns) (p < 0.05). Compared with left and right patterns combined, the indeterminate pattern appears significantly more commonly in incomplete than in complete intraventricular block 03 < 0.0011, for all subjects, with and without known coronary heart disease. As tested in the logistic model, both age and sex have highly statistically significant associations with QRS interval prolongation, with p < 0.001. Thus the evaluation of other associated factors adjusts for them both (Table III). The strongest correlates (here indicated by the nonstandardized p coefficients with the lowest probability values) comprise many manifestations of coronary heart disease, congestive heart failure, atrioventricular block, and

It. Distribution of QRS interval by sex: The Framingham study

Table

QRS

Men

Women

interval (seconds)

No.

%

NO.

%

0.04 0.05 0.06 0.07 0.08 0.09 0.10 0.11 0.12 0.13 0.14 0.15 0.16 0.17 0.18

6 11 223 290 2818 282 94 29 87 4 16 2 2 0 1

0.15 0.28 5.77 7.50 72.91 7.30 2.43 0.75 2.25 0.10 0.41 0.05 0.05 0.03

12 29 431 464 3327 155 44 8 39 5 7 0 6 0 0

0.27 0.64 9.52 10.25 73.49 3.42 0.97 0.18 0.86 0.11 0.15 0.13 -

treatment with digitalis and/or quinidine. Hypertension, left ventricular hypertrophy, and ventricular premature beats are significantly but less strongly associated. Almost two thirds of those with any degree of intraventricular block have at least one of these identified findings. For the rest of the itemssupraventricular premature beats, atrial fibrillation, serum cholesterol level, diabetes mellitus, hematocrit level, stroke, transient ischemic attacks, cigarette smoking, forced vital capacity, and obesity-

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PERCENT 40

40-49

u

SO-59

t

60-69

70+

AGE-.GROUP Fig. 3.

2omplete block pattern S by age group.

Table III. Factors examined for associationwith intraventricular block by logistic regressionadjusted for age and sex Variable

*

Coronary heart disease Ahgina pectoris Coronary insufficiency Myoctirdial infarction ECG myocardial infarction Congestive heart failure Hypertension Systolic blood pressure (mm Hg) Diastolic blood pressure (mm Hg) ECG left ventricular hypertrophy Premature beats (any) Ventricular premature beats Supraventricular premature beats Atrioventricular block Atria1 fibrillation Serum cholesterol (mg/dl) Diabetes mellitus Hematocrit ( 5%) StrokePTransient ischemic attack Cigarette smoking Forced vital capacity (L) Obesity (body mass index) Digitalis and/or quinidine treatment ‘For

definitions,

tp < 0.05. sp < 0.01. QJ < 0.001.

see reference

1.

B 0.97§ O.S@ 0.75t 1.29 1.35 1.75 0.41x 0.005st 0.0040 0.74t 0.56$ 0.571: 0.24 0.74s 0.20 -0.0033 0.33 -0.025 0.35 -0.12 -0.0056 0.82 1.115

no significant relation with intraventricular block is seen. Among the standard Framingham cardiovascular risk factors, only hypertension is signifleantly related to intraventricular block. The distribution of various degrees of intraventricular block in subjects with coronary heart disease differs from that among subjects without coronary disease or congestive heart failure (p < 0.001 for men and for women) (Table IV). Accordingly, multivariate analysis of the significantly assoeiated variables from the logistic model was done separately for the large majority of subjects free of these two conditions (Table V). For them, age, sex, hypertension, and atrioventricular block have a significant independent relation to intraventricular block. Finally, Fig. 5 illustrates the percent of the population with QRS intervals in the complete intraventricular block range, in the incomplete intraventricular block range, and with a measurement (0.09 seconds) that usually is considered to be within normal limits. The large male prevalence of complete intraventricular block appears both in subjects with coronary heart disease and in those without it or congestive heart failure. In coronary heart disease, the excess prevalence of complete intraventricular block over subjects without coroniuy heart disease is about nine-fold in women and about five-fold in men. For incomplete block, it is between

Intraventriculur

block prevalence, Framingham

60-69

q

RIGHT

n

LEFT

907

70+

AGE-GROUP Fig. 4. Incomplete block patterns by age group. Table

IV.

Relation of coronary heart disease and/or congestive heart failure to distribution

of intraventricular

Men

No IVB (QRS 5 0.09 set) Incomplete IVB (QRS = 0.10-0.11 se4 Complete IVB (QRS > 0.11 see) CHD,

Coronary

heart disease; CHF, congestive

Women No CHD or CHF

CHD

block

No CHD or CHF

CHD

No.

%

No.

7%

No.

70

No.

70

239

19

24

8

39

13

3345 130 62

94 4 2

191 7 17

89 3 8

4197 56 36

98 1 1

heart failure;

1 Vz- and 2% -fold. Even the most minimal tion above the mode, an interval of only onds, appears excessively prevalent in heart disease: about two-fold in both women.

IVB, intraventricular

prolonga0.09 seccoronary men and

COMMENTS

These data reflect the uncommon occurrence of intraventricular block only 6% of our whole male population and only 2.4% of females, with only half of the blocks in both sexes being complete. Even in age groups with an appreciable prevalence of heart disease, prolonged QRS interval generally, and complete bundle branch block in particular, are infrequent. Our previous reports5e7 have analyzed development of complete intraventricular block in an

block.

adult population and its association with cardiovascular disease, especially coronary heart disease and left ventricular hypertrophy. This report adds prevalence cases of intraventricular block to the analysis, expands the population examined by including Framingham offspring, and addresses not only complete intraventricular block, but also less prolonged QRS intervals. Review of the literature regarding prevalence of intraventricular block shows that instances of congenital and hereditary bundle branch system defects, often with other conduction abnormalities, have been found even in early infancy, but these cases are rare. 8-15 Reports document a tendency toward progressive derangement of conduction, often culminating in complete heart block, but the

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April 1989 Heart Journal

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q AGE-ADJUSTED 15 PERCENT

c] . lo-. 11 SEC

l

CHO

NO CHO

CHII

WOMEN Fig.

5. Association of coronary heart disease(CHD)

V. Factors associatedwith intraventricular block by multivariate logistic regression(people without CHD or CHF) Variable

P

Sex Age Hypertension ECG left ventricular hypertrophy Ventricular premature beats Atrioventricular block Digitalis and/or quinidine treatment

-1.2* 0.024* 0.4q 0.47 0.29 0.57t -0.17

Congestive

heart

. 12+ SEC

NO CHO

MEN

Table

CHD,

.09 SEC

disease;CHF, congestive heart failure.

*p < 0.001. tp < 0.05.

course may extend over years or even decades. Where familial clusters appear, the hereditary pattern suggests autosomal dominance with incomplete penetrance or variable expressivity. Special groups comprise a second source of information about intraventricular block. Among Air Force men on flying duty having routine ECGs, the tendency of right bundle branch block pattern in the young and left bundle branch block in the older men parallels our findings.16 Another large group has been reported from Manitoba.17* l8 The frequency of finding either right or left bundle branch block at entry was quite low (1.5% for right, 0.7% for left) in

with duration of QRS interval.

this population initially free of coronary or valvular heart disease. In both studies, the subjects, all men with an average age of 30.8 years, had to be well enough to be working actively, so that people with disease tended to be omitted from analysis, which possibly resulted in an underestimation of overall prevalence. The largest body of data comes from patients, mostly cardiac patients. Wasserburgerlg has found prevalence rates of complete bundle branch block among the aged to be slightly higher than ours (about 9%) both sexes combined), but his population of 75- to 96-year-old patients were all being seen for a variety of medical problems. In the context of acute myocardial infarction, there is ample documentation of the concurrent finding of intraventricular block.20-26 Of 210 such patients in whom the investigators had prior ECG data, Gann et aLn found that only 40% of these intraventricular blocks were newly developed. There also appear occasional notices of cases of intraventricular block in certain other clinical conditions, including myotonic dystrophy,= hyperthyroidism,% myocardial sarcoidosis,30 “athletic heart” syndrome,31 alcoholic cardiomyopathy,32, 33Prinzmetal’s angina,% idiopathic pulmonary hemosiderosis,35 and acute rheumatic cardi&* Finally, rate-related bundle branch block is a wellknown entity.37-4* Generally speaking, one must conclude that derangement

of intraventricular

conduction

ex-

Volume Number

117 4

pressed as prolonged QRS interval can result from any one of several processes having the common outcome of interruption or atrophy or failure of development of normal conduction pathways. Lev et a1.42 have found pathologic evidence of myocardial ischemia at the junction of the bundle of His with the left bundle branch in cases of complete left bundle branch block, and it seems reasonable to expect that similar lesions could be found to explain other patterns of intraventricular block. Another report by the same group13 describes complete absence of the entire left bundle branch and the first part of the right bundle branch in a child who was part of a family with congenital bundle branch disease. Short of autopsy, the most extensive clinical studies of causes of intraventricular block have been done on military men. Because of various abnormalities found on routine periodic examinations, 325 airmen had coronary angiography; 298 had no cardiovascular symptoms. 43 Among these 325 men, 41 had right bundle branch block and 34 had left bundle branch block; their average ages were 41 and 42 years, respectively. Eight of the men with right and eight of the men with left bundle branch block had coronary artery disease by angiography. It would be useful to know what proportion of similar men without ECG abnormalities or symptoms have similar angiographic findings, but it is unlikely such a study could be justified. The association we have found with left ventricular hypertrophy expands on the reports of others. The relation is potentially unclear because of the inclusion of QRS intervals of 0.09 to 0.11 seconds in some definitions of ECG left ventricular hypertrophy.44 Zmyslinski et al. 45 looked especially at anatomic left ventricular hypertrophy in 43 instances of left bundle branch block history among 2500 consecutive necropsies and found 41 of the 43 with left ventricular hypertrophy by measurement. Half of these 41 had also had ECG left ventricular hypertrophy, which, when it antedated the appearance of left bundle branch block, was noted to become less prominent by voltage criteria after the development of the block. Those with both left bundle branch block and ECG left ventricular hypertrophy had the most extreme anatomic left ventricular hypertrophy. Cokkinos et al.& also discuss the potential difficulties of diagnosing ECG left ventricular hypertrophy in the presence of left bundle branch block, but conclude that voltage criteria still hold. Thus prolonged QRS interval travels in company with cardiovascular disease, much of it clinically significant. It is seen in conjunction with symptom-

Intrauentricular

block prevalence, Framingham

909

atic and asymptomatic disease affecting the myocardium primarily or the coronary arteries. Even durations as small as 0.09 seconds show up twice as often in people with coronary heart disease as in those without it. Whether the finding of isolated intraventricular block warrants major investigation in people without symptoms has been addressed and answered in the negative. 47,48In others, however, it may be a sign worth watching. Subsequent investigations will address the cardiovascular outcome of Framingham subjects with intraventricular block, in an attempt to establish the prognostic significance of this ECG finding. SUMMARY

QRS intervals in the ECGs of members of the Framingham Heart Study cohort and offspring were measured to provide an estimate of the prevalence of intraventricular block in the general population. Intervals of 2 0.09 second appear in men twice as commonly as in women, are rare before age 50 to 60, and shift from a predominance of right bundle branch block in the young to an indeterminate pattern in the elderly. Complete intraventricular block (QRS interval 2 0.12 second) is seen in 11% of elderly men and 5% of elderly women. Aside from age and sex, logistic regression indicates strong associations with concurrent manifestations of coronary heart disease, congestive heart failure, and atrioventricular block, as well as hypertension, left ventricular hypertrophy, and ventricular extrasystoles. Among those subjects free of clinical coronary disease and congestive heart failure, associations between QRS interval and age, sex, atrioventricular block, and ECG left ventricular hypertrophy remain significant by multivariate analysis. Whether people with prolonged QRS intervals need special monitoring or attention cannot be told from these data. Thanks go to Lisa Provencher, BS, for statistical onset of this study and to Georgieanna Remillard, utmost patience in secretarial support.

help at the ASS, for

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