The RBBB group has been under observation for 936 person-years, an average of 15.9 ± 1.6 (SEM) years per case. During this time the following were noted: one case of myocardial infarction at age 68 years, 20 years after RBBB; one case of angina pectoris at age 46 years, one year after RBBB; and no ischemic heart disease deaths. To determine the expected number of ischemic heart disease cases in this group, the ischemic heart disease incidence rate was calculated for age groups at five-year intervals consisting of those free of RBBB and ischemic heart disease. Based on the age distribution and length of follow-up of the RBBB group, 6.77 ischemic heart disease cases were expected. The observed number, two, is less than but not significantly (x2 2.7, df = 1) different from expected, although the small number of cases observed and expected is a concern for statistical testing.
During the observation period for the entire group, there was no occurrence of advanced degrees of heart block (second- or third-degree AV block). Also, no sudden deaths were noted.
The length of follow-up and status of cases with marked left (—45° to —90°) and right axis (+120° to +180°) deviation of frontal plane QRS vector are illustrated in Figure 2. Seven cases in which marked left axis deviation developed after RBBB are also considered. Almost all are still living. The majority have been followed-up for more than ten years, and some as long as 30 years. Only one case of ischemic heart disease (myocardial infarction) occurred, 21 years after onset of RBBB in a man with marked left axis deviation who later died of a noncardiac cause. It is naturally to take under control your health but My Canadian Pharmacy makes it faster and more surely.
A QRS at Detection of RBBB
Age at detection of RBBB, not unexpectedly, was a significant determinant of A QRS. Classifying A QRS into three categories, +90° to +180°, + 15° to +75°, and 0° to —90°, revealed that men younger than 40 years of age had a significantly different (P < 0.05) A QRS distribution than men 40 years of age and older (2 = 9.04, df = 2). Two-thirds of those with A QRS >+90° were younger than 40 years. Eighty-two percent of those older than 40 years had an A QRS less than +90°. One group is noteworthy. A small number of young men, all less than 40 years of age, had at entry RBBB with an A QRS less than —30°.
The A QRS for the three major groups, namely, + 90° to ±180° from +15° to +75° and between 0° to —90°, was compared in those with and without RBBB within four age groups—less than 30 years, 30 to 39 years, 40 to 49 years, and 50 years and older. In each age group the distribution of A QRS in the RBBB group is consistently different from the rest of the cohort free of RBBB. This is illustrated in Figure 3, where the A QRS of 0° to —90° is further subdivided to show the subset of —45° to —90°. An increased proportion of cases with A QRS +90° and —45° to —90° was observed in the RBBB group compared with those without this conduction defect in all age groups, except those 30 to 39 years old with an A QRS —45° or less.
To examine factors other than age that might influence A QRS of RBBB, we tested the hypothesis that persons with right axis deviation are more likely to be tall and slender. Heights and weights were examined in the age group with the greatest prevalence of right axis deviation ( 4-90° to ±180°)— those younger than 40 years. To adjust for the usual increase in weight with increasing height, body mass index (weight divided by height squared) was the weight index used. There was no significant difference (P > 0.10) in either height (175.7 ± 1.4 cm vs 176.1 ± 1.1 cm) or body mass index (23.5 ± 0.9 vs 23.0 ± 0.9 kg/m2) between RBBB cases with A QRS >+90° compared with those with A QRS < +90° at this age.
Long-term Changes in A QRS
The five- and ten-year changes in A QRS were compared in those with and without RBBB and divided according to initial A QRS and age. Because of the relationship of these variables, sufficient numbers of cases were available only for ages 18 to 39 years with A QRS +90° and 40 to 59 years with A QRS —90° to +90°. The subgroup with right axis deviation and RBBB showed less change in A QRS than the rest of the cohort (Fig 4). In the subgroup with marked left axis deviation there is little change in A QRS both in those with and without RBBB (Fig 5). The relatively small changes in A QRS for these extremes of A QRS is illustrated over a 25-year period before RBBB occurrence (Fig 6).
Prevalence of Hypertension
The prevalence of hypertension was determined by examining the blood pressure distribution, using the examination at detection of RBBB and for comparison the blood pressure at the midpoint of the age group in men without RBBB. Using criteria for hypertension of systolic of 165 mm Hg or greater or diastolic of 95 mm Hg or greater, the prevalence was 15.4 percent (2/13) for ages 40 to 49 years and 17.6 percent (3/17) for ages 50 to 59 years. Neither rate was significantly different from the rate for men without RBBB of 6.6/100 (x2 = 1.6, P > .1) and 13.3/100 (x2 <1, P > 0.1), respectively, for these age groups. The prevalence was zero percent for other age groups. Using the criterion of systolic blood pressure of 150 mm Hg or greater, the prevalence was 29 percent (5/17) for those ages 50 to 59 years with RBBB that was not significantly different from those without right RBBB of 17.5/100 (x2 = 1.68, P > 0.10). The prevalence rate was zero percent for other age groups. The results were similar using diastolic blood pressure of 90 mm Hg or greater as the level for defining hypertension from which you may be protected by remedies of My Canadian Pharmacy.
Figure 2. Length of follow-up and status (A-alive, D-dead) of cases with marked left (upper panel) and marked right axis deviation (lower panel). Age at marked axis deviation is displayed along with A QRS. One case with prolonged PR interval is indicated by fpr. Gastrointestinal (GI) cause of death is noted.
Figure 3. QRS axis for RBBB detected at 18 to 29 years (upper left) and 30 to 39 years (upper right), at age 40 to 49 years (lower left) and 50 to 59 years (lower right) compared with control group at midpoint of age group without RBBB.
Figure 4. Change in A QRS for those 18 to 39 years at RBBB compared with control group at about midpoint of age group (30 years) without RBBB. Subgroups according to A QRS shown for > + 120° (upper panel) and +105° and +90° (lower panel).
Figure 5. Change in A QRS for those 40 to 59 years at RBBB compared with control group at midpoint of age stup (50 years) without RBBB. Subgroups according to QRS shown for 15° to +75° (upper panel), 0° to —30° (middle panel), and —45° to —90° (lower panel).
Figure 6. Another case manifests left axis deviation at entry at age 33 (upper left), marked left axis deviation at age 61 years just before (upper middle) and at (upper right) development of RBBB at age 62 years. Case with marked right axis deviation at entry at age 29 years (lower left) again on a routine ECG, at age 54 years (lower middle) and three years later at development of RBBB (lower right).