CORRESPONDENCE: RESEARCH CORRESPONDENCE
Association Between Right Bundle Branch Block and Impaired Myocardial Tissue-Level Reperfusion in Patients With Acute Myocardial Infarction
Makoto Suzuki, MD*,
Tomoki Sakaue, MD,
Masamichi Tanaka, MD,
Eiki Hirose, MD,
Hideyuki Saeki, MD,
Tsuyoshi Matsunaka, MD,
Shinichi Hiramatsu, MD and
Yukio Kazatani, MD
* Division of Cardiology, Ehime Prefectural Central Hospital, 83 Kasuga, Matsuyama, Ehime 790-0024, Japan (Email: suzuki-m{at}mail.netwave.or.jp).
To the Editor: The new onset of right bundle branch block (RBBB) was identified as a potent predictor of adverse outcome in patients with ST-segment elevation myocardial infarction (STEMI) in the thrombolytic era (1). In the primary percutaneous coronary intervention (PCI) era (2), well-preserved myocardial tissue-level reperfusion has been shown to be a prerequisite for improved clinical outcome in patients with STEMI (3,4).
In the present study, we evaluated the clinical benefit of PCI in patients with a first anterior STEMI complicated by RBBB and investigated the association between RBBB and impaired myocardial tissue-level reperfusion in those patients in whom PCI provided little benefit.
A total of 105 consecutive patients with a first anterior STEMI due to proximal occlusion of the left anterior descending coronary artery were divided into two groups according to the presence or absence of RBBB on admission. The RBBB was considered new if it was not apparent on a previous electrocardiogram or if no previous tracing was available (1).
Culprit epicardial coronary flow was evaluated by the Thrombolysis In Myocardial Infarction (TIMI) flow grade with an assessment of Rentrop collateral grade. Successful PCI was defined as adequate restoration of coronary artery patency (TIMI flow grade 2 or 3) and <50% postprocedural diameter stenosis in the culprit. To evaluate myocardial tissue-level reperfusion, TIMI myocardial perfusion (TMP) grade (5) and resolution of the sum of ST-segment elevation in leads I, aVL, and V1 through V6 after PCI (6) were analyzed by two observers blinded to the patient’s identity. Impaired myocardial tissue-level reperfusion was defined by the presence of both a TMP grade of <3 and resolution of the sum of ST-segment elevation of <50% after coronary angioplasty (4). With a two-compartment model, enzymatic infarct size was defined as the area under the curve of plasma levels of creatine kinase-myocardial band fraction, which were measured every 4 h during the first 24 h after admission. During a mean follow-up period of 22 ± 14 months after discharge, the incidence of major adverse cardiovascular events (MACE) such as death from cardiac diseases, myocardial infarction, hospital stay for heart failure, and ischemia-driven target-vessel revascularization were obtained by either a review of the hospital records or telephone contact with the patients.
Continuous variables are presented as mean ± SD, and comparisons were made by an unpaired t test or a Mann-Whitney U test in accordance with data distribution. Categorical variables were compared by a chi-square test. A logistic-regression analysis with calculation of odds ratio was performed to evaluate the independent relations of selected variables to impaired myocardial tissue-level reperfusion. The p values were determined by two-tailed tests.
A total of 24 patients (23%) showed RBBB on admission. Baseline clinical and angiographic characteristics according to the presence or absence of RBBB are shown in Table 1. An increased ratio of patients with diabetes mellitus and Killip III or IV was observed in the RBBB group. Culprit coronary lesions were recanalized in all patients, and the incidence of a final TIMI flow grade 0 or 1 was three patients with RBBB and four without (13% vs. 5%, p = 0.399). Calculated enzymatic infarct size was greater in patients with RBBB than in those without (10,350 ± 6,557 IU/l vs. 7,262 ± 5,240 IU/l, p = 0.025). A >50% resolution in the sum of ST-segment elevation was obtained in only 4 patients with RBBB as compared with 52 without (17% vs. 64%, p = 0.001). Seven patients with RBBB and nine without showed a paradoxical ST-segment elevation after PCI (29% vs. 11%, p = 0.031). A TMP grade 3 was achieved in 9 patients with RBBB, in contrast to 62 without (38% vs. 77%, p = 0.001) (Fig. 1A). Impaired myocardial tissue-level reperfusion, defined by the presence of both TMP grade <3 and ST-segment resolution <50%, was seen in 12 patients with RBBB in contrast to 6 without (50% vs. 7%, p < 0.001) (Fig. 1B). Seven patients with RBBB and three without maintained a Killip class IV status over 24 h after PCI (29% vs. 4%, p < 0.001). In-hospital death occurred in three patients with RBBB and in two without (13% vs. 3%, p = 0.036). In a logistic-regression analysis, RBBB was strongly associated with impaired myocardial tissue-level reperfusion (odds ratio, 9.47; 95% confidence interval, 2.71 to 33.07; p < 0.001). Three patients with RBBB and 56 without were categorized as New York Heart Association functional class I at discharge (13% vs. 69%, p < 0.001). Nine patients with RBBB and 15 without experienced MACE after discharge (43% vs. 19%, p = 0.023). Of those with MACE at follow-up, six patients with RBBB and two without presented with impaired myocardial tissue-level reperfusion at PCI (67% vs. 18%, p = 0.007).
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Table 1. Baseline Clinical and Angiographic Characteristics of 105 Patients With a First Anterior STEMI, According to the Presence or Absence of RBBB
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Figure 1 (A) Thrombolysis In Myocardial Infarction myocardial perfusion (TMP) grade by the presence or absence of right bundle branch block (RBBB) in 105 patients with ST-segment elevation myocardial infarction (STEMI). (B) Myocardial tissue-level reperfusion by the presence or absence of RBBB in 105 patients with STEMI.
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These findings suggested that patients treated with primary PCI for a first anterior STEMI complicated by RBBB show a high incidence of MACE both during admission and after discharge. With the integrated analysis of TMP grade and resolution of the sum of ST-segment elevation, which has been shown to be a simple and reliable marker for real-time grading of microvascular reperfusion (4), we found a strong association between RBBB in these patients and marked damage on myocardial tissue-level reperfusion followed by a subsequent high incidence of MACE.
Because the dual vascular supply of the right bundle branch might be expected to provide a degree of protection against the adverse effects of ischemia, STEMI accompanied by RBBB is recognized as a more serious form of myocardial ischemia (7). In fact, we observed that 46% of patients with RBBB showed Killip class III or IV heart failure on admission, with no relation seen with plasma levels of creatine kinase-MB. Reperfusion of a severely ischemic myocardium might result in lethal reperfusion injury, characterized by marked endothelial cell dysfunction, as well as irreversible myocyte damage, possibly arising from inflammatory reactions (8). The extensive appearance of ultrastructural myocardial cellular edema and microvascular damage soon after coronary occlusion is likely an important representative pathophysiological finding in impaired myocardial tissue-level reperfusion (8).
In summary, these results suggest that the presence of impaired myocardial tissue-level reperfusion in patients with RBBB-complicating STEMI might confer a high risk of MACE, even in the primary PCI era. Effective treatment and prevention of MACE in these high-risk patients might require the adoption of novel and drastic methods to improve myocardial tissue-level reperfusion.
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References
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