This study demonstrated the relationship between the presence of f-wQRS in patients with LBBB on surface ECG and the presence and severity of CAD. This finding of f-wQRS in patients with LBBB may be thought to be an additional risk factor for CAD.
The relationship between CAD and LBBB has been evaluated in epidemiologic studies. Framingham study reported that CAD was more frequent in patients with LBBB and that the presence of LBBB in CAD patients was an independent predictor of mortality [1
]. For this reason, it is very important to investigate the presence of CAD in LBBB patients; however, the use of non-invasive tests for the evaluation of CAD in LBBB cases is limited.
The non-invasive procedures for the investigation of CAD in LBBB cases include evaluation of the clinical risk factors, Myocardial Perfusion Scintigraphy [MPS], cardiopulmonary exercise test, stress echocardiography and metabolic tests. The male
gender, decreased ejection fraction [<55%] and advanced age have been reported as clinical risk factors for the development of CAD in LBBB cases [13
]. Exercise ECG, a non-invasive test that is often used in the investigation of CAD, has limited diagnostic value in LBBB patients. The ACC/AHA Guide recommends the use of pharmacological stress test and MPS for the investigation of ischemia in LBBB cases [14
]. However, due to the heterogenous effect of LBBB on myocardial structure, functions and perfusion in such patients, defects in MPS, anteroseptal and septal perfusion can also be observed in the absence of CAD [15
]. Krishnan et al. reported that the sensitivity of MPS in LBBB patients was 96% [for LAD: 84%, for CX: 50%, for RCA: 100%], and that the specificity of MPS in LBBB patients for LAD was 39%, for CX: 95%, and for RCA: 68% [17
A recent study has asserted that in patients with chest pain and LBBB undergoing cardiopulmonary exercise test, new functional parameters such as the time needed to reach the anaerobic threshhold could be a predictor for CAD [18
]. Vasconcelos et al. reported that on exercise stress echocardiography of LBBB cases, degeneration in the septal wall thickening was a sign of ischemia and an independent predictor of mortality in those with CAD [19
The non-invasive tests used in the investigation of CAD in cases of LBBB are unavailable in some centers and are generally expensive or time-consuming. This situation has led to the search for a new CAD predictor that would be easier to evaluate. In these patients, the ECG
findings related to CAD display differences. It has been reported that in the presence of LBBB, the Sgarbossa criteria should be used for the diagnosis of ST segment elevation MI [20
]. Again, in these patients, the findings of past Myocardial Infarction (MI) display differences. In patients with LBBB, while Q wave or T wave inversion on the aVF lead demonstrates past inferior MI with 86% sensitivity and 91% specificity, there is no ECG finding that demonstrates past anterior or lateral MI [21
Das et al. have reported that in cases with known or suspected CAD, the presence of f-wQRS on surface ECG with 12 derivations indicating myocardial scarring, which is normally evaluated with single photon emission computed tomography, has mid-sensitivity [62.2%] and high specificity [94%]. In their study which included patients with LBBB and RBBB, the survival time in patients with fragmented LBBB was determined to be significantly shorter than that in patients with non-fragmented LBBB, RBBB and fragmented RBBB [22
]. Our study showed that in LBBB cases with no history of MI, there was a relationship between fragmented wide QRS and CAD with clinically significant stenosis on coronary angiography. The fragmented wide QRS in the CAD group was attributed to the patch-like fibrosis caused by ischemia or scar tissue caused by silent infarction. In our study, the presence of f-wQRS in patients with LBBB for documenting severe CAD was found to have 82.1% sensitivity and 91.7% specificity. This finding suggests that the presence of f-wQRS in this patient group may be non-invasive criteria for the investigation of CAD.
The mechanism of fragmented QRS formation is not fully known. However, conditions that cause non-homogenous depolarization in the myocardium such as scarring, fibrosis and ischemia have been implied as related factors [3
]. As well as coronary ischemia, cardiac infiltrative diseases such as amyloidosis and beta-thalassemia and the conditions which causes increased left ventriculer mass such as hypertension and severe aortic stenosis can lead to f-wQRS formation [23
]. In a histopathological study, it has been demonstrated that coronary ischemia can also cause patch-like fibrosis without infarction [26
]. Kadi et al. have reported that in patients with chronic total occlusion with no history of MI, the presence of fragmented QRS on the surface ECG is related to insufficient development of coronary collateral artery [27
]. Apart from determining the presence of fragmented QRS, it is also important to determine the number of derivations displaying fragmented QRS and in which derivations the fragmented QRS is present. It has been reported that more myocardial tissue is under risk in ST saegment elevation MI cases with fragmented QRS, and the decrease in the number of derivations with fragmented QRS after primary percutaneous coronary intervention is related to a higher resolution in the ST segment [28
]. With regard to these findings, it is considered that fragmented QRS could also be present due to ischemia without infarction. In our study, the presence of f-wQRS in patients with left bundle branch block was associated with the presence and severity of obstructive CAD. It is also important that presence of f-wQRS was associated with high Gensini score which is used to assess the severity and extent of CAD.