Abstract
Objective: To evaluate left bundle branch block (LBBB) as an indicator of advanced cardiovascular involvement in diabetic (DM) patients by examining left ventricular systolic function and proteinurea.
Methods: Data of 26 diabetic patients with left bundle branch block (DM with LBBB) were compared with data of 31 diabetic patients without left bundle branch block (DM without LBBB) and 18 nondiabetic patients with left bundle branch block (non‐DM with LBBB). The inclusion criteria were age >45 years, and diabetes mellitus type 2 of >5 years.
Results: Mean ages of patients in DM with LBBB, DM without LBBB, and non‐DM with LBBB groups were 67 ± 8, 68 ± 10, and 65 ± 10 years, respectively (P = NS). Females were 65%, 61%, and 61%, respectively (P = NS). Left ventricular ejection fraction in DM with LBBB was significantly lower than in DM without LBBB and non‐DM with LBBB (30 ± 10% vs 49 ± 12% and 47 ± 8%, P < 0.01). Left ventricular end‐diastolic volume was significantly higher in DM with LBBB than in DM without LBBB and non‐DM with LBBB (188.6 ± 16.4 mL vs 147.5 ± 22.3 mL and 165.3 ± 15.2 mL, P < 0.03). Similarly, left ventricular end‐systolic volume was significantly higher in DM with LBBB than in DM without LBBB and non‐DM with LBBB (135.4 ± 14.7 mL vs 83.7 ± 9.5 mL and 96.6 ± 18.4 mL, P < 0.02). No statistically significant difference was seen in left atrial size. Proteinurea in DM with LBBB (79.4 ± 18.9 mg/dL) was significantly higher than in DM without LBBB (35.6 ± 8.5 mg/dL, P < 0.05) and non‐DM with LBBB (12 ± 3.5 mg/dL, P < 0.05); however, there was no significant difference in Hb A1c levels in DM with LBBB and DM without LBBB (9.01% vs 7.81%, P = NS).
Conclusions: Left bundle branch block in diabetic patients indicates advanced cardiovascular involvement manifesting with more severe left ventricular systolic dysfunction and proteinurea compared to both diabetic patients without left bundle branch block and nondiabetic patients with left bundle branch block.
Keywords: diabetes mellitus, left bundle branch block, diabetic cardiomyopathy, proteinurea, diabetic microangiopathy, cardiovascular diabetology
Diabetes mellitus (DM) is a major risk factor for cardiovascular disease including microangiopathy and accelerated atherosclerosis with more severe, extensive, and diffuse lesions compared to those in nondiabetic patients. 1 , 2 , 3 Similarly, diabetic cardiomyopathy is a well‐recognized complication of diabetes mellitus and occurs in the absence of ischemic, vascular, and hypertensive disease. 4 , 5 , 6 The left bundle branch block (LBBB) has been identified as an important feature in idiopathic dilated cardiomyopathy, and has also been reported in diabetic cardiomyopathy. 7 The objective of this study was to evaluate left bundle branch block as an indicator of advanced cardiovascular involvement in diabetic patients by examining left ventricular systolic function and proteinurea.
METHODS
Data of 26 diabetic patients with left bundle branch block (DM with LBBB) were compared with data of 31 diabetic patients without left bundle branch block (DM without LBBB) and 18 nondiabetic patients with left bundle branch block (non‐DM with LBBB). Diabetic patients (both with and without LBBB) were selected from the cardiology clinic of Woodhull Medical Center in a consecutive fashion for the study in a period of 3 years. The inclusion criteria were age >45 years, and diabetes mellitus type 2 of >5 years. Matched controls were selected who were nondiabetic but had left bundle branch block (non‐DM with LBBB). Age, sex, race, ethanol use, hypertension, and coronary artery disease were matched among three groups. Hypertension was defined if patients had a history of hypertension or if they were on antihypertensive medications. Coronary artery disease was defined as if patients had a history of myocardial infarction, had angina pectoris with a positive stress rest, or had coronary angiography done which had shown a decrease in lumen diameter of >50% in one or more of the major epicardial coronary arteries or their primary branches. Echocardiography was done as part of the protocol. The echocardiographic left ventricular ejection fraction and left ventricular end‐systolic and end‐diastolic volumes were recorded and compared among groups. Laboratory data for hemoglobin A1c (Hb A1c) and urine protein was recorded for all patients.
The continuous variables were expressed as mean and analyzed by Student's t‐test. The categorical variables were expressed as a percentage and analyzed by chi‐square statistics or Fisher's exact test as appropriate. A 2‐tailed P value of 0.05 or less was considered significant. All the statistical analyses were performed using computer software, SPSS 7.0 (SPSS Inc., Chicago, IL).
RESULTS
The mean ages of patients in DM with LBBB, DM without LBBB, and non‐DM with LBBB groups were 67 ± 8, 68 ± 10, and 65 ± 10 years, respectively (P = NS). Females were 65%, 61%, and 61%, respectively, in DM with LBBB, DM without LBBB, and non‐DM with LBBB groups (P = NS). Left ventricular ejection fraction in DM with LBBB patients was significantly lower than in DM without LBBB and non‐DM with LBBB patients (30 ± 10% vs 49 ± 12% and 47 ± 8%, P < 0.01). Left ventricular end‐diastolic volume was significantly higher in DM with LBBB patients than in DM without LBBB and non‐DM with LBBB patients (188.6 ± 16.4 mL vs 147.5 ± 22.3 mL and 165.3 ± 15.2 mL, P < 0.03). Similarly, left ventricular end‐systolic volume was significantly higher in DM with LBBB patients than in DM without LBBB and non‐DM with LBBB patients (135.4 ± 14.7 mL vs 83.7 ± 9.5 mL and 96.6 ± 18.4 mL, P < 0.02). No statistically significant difference was seen in left atrial size (4.0 ± 0.2 cm in DM with LBBB vs 4.3 ± 0.5 cm in DM without LBBB vs. 3.8 ± 0.4 cm in non‐DM with LBBB, P = NS). Proteinurea in DM with LBBB patients (79.4 ± 18.9 mg/dL) was significantly higher than in DM without LBBB (35.6 ± 8.5 mg/dL, P < 0.05) and non‐DM with LBBB patients (12 ± 3.5 mg/dL, P < 0.05); however, there was no significant difference in Hb A1c levels in DM with LBBB and DM without LBBB patients (9.01% vs 7.81%, P = NS) (Table 1).
Table 1.
Data of Diabetic Patients with Left Bundle Branch Block versus Diabetic Patients without Left Bundle Branch Block and Nondiabetic Patients with left Bundle Branch Block
| Characteristics | DM with LBBB (n = 26) | DM without LBBB (n = 31) | Non‐DM with LBBB (n = 18) | P value* |
|---|---|---|---|---|
| Age (years) | 67 ± 8 | 68 ± 10 | 65 ± 10 | NS |
| Females | 17 (65%) | 19 (61%) | 11 (61%) | NS |
| LV ejection fraction | 30 ± 10% | 49 ± 12% | 47 ± 8% | < 0.01 |
| LV end‐diastolic volume mL | 188.6 ± 16.4 | 147.5 ± 22.3 | 165.3 ± 15.2 | < 0.03 |
| LV end‐systolic volume, mL | 135.4 ± 14.7 | 83.7 ± 9.5 | 96.6 ± 18.4 | < 0.02 |
| Left atrial size, cm | 4.0 ± 0.2 | 4.3 ± 0.5 | 3.8 ± 0.4 | NS |
| Urine proteins, mg/dL | 79.4 ± 18.9 | 35.6 ±8.5 | 12 ± 3.5 | < 0.05 |
| Glycemic control, Hb A1c | 9.01% | 7.81% | N/A | NS |
*P value of comparison between DM with LBBB versus DM without LBBB and non‐DM with LBBB.
DM = Diabetes mellitus; Hb = Hemoglobin; LBBB = Left bundle branch block; LV = Left ventricular; N/A = Not applicable; NS = Nonsignificant.
DISCUSSION
This study demonstrated that the presence of left bundle branch block in diabetic patients is associated with advanced cardiovascular disease with more severe left ventricular dysfunction and proteinurea. Incidence and prevalence of diabetes mellitus has increased significantly due to aging of population, increasing obesity, and decrease in physical activity. 1 , 8 This is exclusively due to increase in type 2 diabetes mellitus, which represents more than 90% of the all cases of diabetes mellitus. Diabetic patients have a considerable risk for cardiovascular disease and up to 80% of deaths within this group of patients are from cardiovascular disease. 9 Macro‐ and microvascular disease like myocardial infraction, stroke, peripheral vascular disease, and microangiopathy accounts for the majority of morbidity and mortality associated with type 2 diabetes mellitus. 10 , 11 Diabetes remains an independent predictor of congestive heart failure and of mortality among patients with congestive heart failure. 12 , 13
Left bundle branch block is commonly associated with dilated cardiomyopathy. We studied left bundle branch block and left ventricular size and function in diabetic patients by selecting diabetic patients with left bundle branch block and comparing their echocardiographic findings with diabetic patents without left bundle branch block and nondiabetic patients with left bundle branch block. Interestingly, we found that patients with both left bundle branch block and diabetes mellitus had more severe left ventricular dysfunction compared to diabetic patients without left bundle branch block and nondiabetic patients with left bundle branch block; all groups were matched for comorbid conditions, age, race, and sex. Similarly, patients with both left bundle branch block and diabetes mellitus had larger left ventricular volumes compared to diabetic patents without left bundle branch block and nondiabetic patients with left bundle branch block. These patients were also found to have a higher level of proteinurea, even though no significant difference was found in serum level of Hb A1c.
Many studies of left bundle branch block, particularly in earlier literature, have concluded that left bundle branch block is associated with advanced cardiac disease and poor prognosis. 14 , 15 , 16 , 17 Significant left ventricular systolic and diastolic function is known to develop due to abnormal sequence of left ventricular activation, and the concept of biventricular pacing in persistent recurrent heart failure is based on correcting this abnormal sequence of activation of left ventricular by simultaneously activating both the septum and the lateral wall. Left bundle branch block in idiopathic dilated cardiomyopathy may reflect the diffuse disease of left ventricle or it may be secondary to involvement of left bundle in initial myocarditis. Left bundle branch block in diabetes mellitus associated with severe left ventricular dysfunction may reflect the diffuse involvement of left ventricle in diabetes mellitus. Our study also showed that patients with left bundle branch block were more likely to have higher amounts of protein in urine. The presence of proteinurea is a manifestation of the development of renal microangiopathy, which is a sign of generalized vascular microangiopathy; vascular microangiopathy is the mechanism proposed for the development of diabetic cardiomyopathy. 18 , 19 , 20
CONCLUSION
Left bundle branch block in diabetic patients indicates advanced cardiovascular involvement manifesting with more severe left ventricular systolic dysfunction and proteinurea compared to both diabetic patients without left bundle branch block and nondiabetic patients with left bundle branch block. Therefore, diabetic patients with left bundle branch block should be evaluated for left ventricular systolic dysfunction and proteinurea in order to institute appropriate preventive measures.
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