Assessment of myocardial perfusion with thallium-201 scintigraphy in exercise-induced left bundle branch block: diagnostic value and clinical significance

Rate-related left bundle branch block and cardiac memory in a patient with bradycardia: Case report and literature review

Rate-related left bundle branch block (LBBB) is a well-studied phenomenon. Cardiac memory is another physiologic phenomenon in which T-wave abnormalities occur in the absence of ischemia. The association between these 2 phenomena has been described in several case reports. A literature review was performed through Ovid and PubMed, where at total of 93 cases of rate-related LBBB were identified. Cases were reviewed, and data were collected on rates of appearance and disappearance as well as the presence or absence of cardiac memory. There is some overlap in the rate at which LBBB appears. Cardiac memory is associated with rate-related LBBB in several cases, but its true prevalence is unknown. Cardiac memory is a phenomenon that is well described in the literature but is often underrecognized in clinical practice. As a consequence of overlooking this phenomenon and not including cardiac memory in the differential when T-wave abnormalities are observed, patients may be subjected to unnecessary invasive diagnostic testing.

Accuracy of non-invasive techniques for diagnosis of coronary artery disease and prediction of cardiac events in patients with left bundle branch block: a meta-analysis

PURPOSE

Non-invasive evaluation of coronary artery disease (CAD) in patients with left bundle branch block (LBBB) has limitations inherent to different tests, and the relative merits of these tests are unclear. This meta-analysis assessed the accuracy of the frequently used non-invasive techniques, including exercise electrocardiography (ECG), myocardial perfusion imaging (MPI) and stress echocardiography (SE), for detection of CAD and prediction of cardiac events in patients with LBBB.

METHODS

A review was conducted of all reports on detection of CAD and prediction of cardiac events in patients with LBBB (published between January 1970 and December 2004), and revealed 55 diagnostic and nine prognostic reports with sufficient details to calculate test accuracy. Weighted (by sample size) sensitivity and specificity were calculated. Summary relative risk ratios (95% confidence intervals) were calculated.

RESULTS

Overall sensitivity was higher for exercise ECG and (quantitatively analysed) MPI than for SE (83.4% and 88.5% versus 74.6% respectively, p<0.0001). SE had a higher specificity (88.7%) than MPI (41.2%) and exercise ECG (60.1%) (p<0.0001). Based on analysis of eight reports, the relative risk of cardiac death or myocardial infarction in patients with an abnormal SE and MPI was elevated more than sevenfold, but it did not differ by imaging modality (p=0.9).

CONCLUSION

Meta-analysis of non-invasive CAD assessment in LBBB patients revealed that exercise ECG and MPI had the highest sensitivity, while SE had the highest specificity. The prognostic accuracy of MPI and SE appeared similar.

Technetium-99m-Sestamibi SPECT myocardial perfusion imaging in patients with complete left bundle branch block

BACKGROUND

Diagnosis of coronary artery disease (CAD) in patients with left bundle branch block (LBBB) is considered a challenge in cardiology due to low accuracy of noninvasive methods such as basal and exercise stress test. Recently, myocardial perfusion imaging showed attainment of higher sensitivity and specificity. Scintigraphy with thallium-201 has been widely used in these patients. Few have used technetium-99m-Sestamibi and single photon emission computed tomography (SPECT). The aim of the study was to assess the diagnostic value of Tc-99m Sestamibi SPECT myocardial perfusion imaging in patients with complete LBBB.

METHODS

We studied 57 consecutive patients with complete LBBB using Tc-99m-Sestamibi SPECT and treadmill or dipyridamole stress to evaluate CAD. Eighteen patients also underwent coronary angiography. Perfusion defects were classified as fixed or reversible.

RESULTS

Prevalence of resting perfusion abnormalities in anterior, septal, and apical regions was 51, 56, and 19%, respectively. Sensitivity for detecting >50% left anterior descending artery (LAD) stenosis was 67 and 56% for anterior or septal defects, and 56% for specificity. Apical perfusion abnormality showed 21% sensitivity and 89% specificity. Among six patients with reversibility and who underwent coronary angiography, all had >50% LAD stenosis.

CONCLUSIONS

With Tc-99m-MIBI SPECT imaging, prevalence of anteroseptal perfusion abnormalities was >50% in patients with LBBB. The test has moderate sensitivity and specificity for LAD disease. Absence of apical defect is specific for excluding LAD disease. Reversible changes in anteroseptal wall should be considered as an indicator of ischemia in this territory.

[Exercise-induced left bundle-branch block in patients with coronary artery disease versus patients with normal coronary arteries]

INTRODUCTION AND OBJECTIVES

Exercise-induced left bundle-branch block does not always denote the presence of underlying coronary artery disease. The aim of this study was to analyze the clinical characteristics and evolution of patients with rate-dependent left bundle-branch block.

PATIENTS AND METHOD

9,318 consecutive exercise stress studies were reviewed. The clinical characteristics and evolution (mean follow-up: 6.9 years) of 20 patients with exercise-induced left bundle-branch block in which coronary angiography had been performed were analyzed.

RESULTS

Eight out of 20 patients had normal coronary arteries (group A) and 12 had coronary artery disease (group B). Peak O2 consumption, peak myocardial O2 consumption, and heart rate when block appeared (132 20 vs. 95.4 23 beats/min; p = 0.002) were significantly higher in group A. Seven of the 8 patients with normal coronary arteries had chest pain coinciding with the first beat of left bundle-branch block. There were no deaths during follow-up in group A, but permanent left bundle-branch block appeared in 5 patients of this group who experienced disappearance of exercise-related pain. There were 3 deaths in group B and 2 patients had acute myocardial infarction during follow-up. One patient in each group developed atrioventricular block and required pacemaker implantation.

CONCLUSIONS

In contrast with patients with left bundle-branch block and coronary artery disease, the prognosis of patients with painful left bundle-branch block and normal coronary arteries is good. However, the development of permanent left bundle-branch block is frequent. Atrioventricular block, although rare, may occur.

Diagnosis of coronary artery disease with Tl-201 SPECT in patients with left bundle branch block: importance of alternative interpretation approaches for left anterior descending coronary lesions

Left bundle branch block (LBBB) is a strong predictor of mortality in the presence of coronary artery disease (CAD). Noninvasive evaluation of CAD in these patients has some difficulties. Exercise-induced electrocardiographic ST segment changes are nondiagnostic, and several scintigraphic studies have reported false-positive anteroseptal and septal perfusion defects up to 80%. The authors aimed to assess the diagnostic accuracy of thallium-201 (Tl-201) exercise myocardial single photon emission computerized tomography (SPECT) in comparison with coronary angiography (CAG) for detection of CAD in patients with LBBB. Seventy-seven consecutive patients suffering from chest pain with complete and permanent LBBB were included in the study. All patients (40 women, 37 men, mean age = 54 +/- 7 years) were studied with Tl-201 exercise SPECT and coronary angiography. Tl-201 exercise SPECT for diagnosis of left anterior descending (LAD) artery lesions was interpreted by using three different approaches: method A (conventional approach), method B (involvement of anterior and septal wall regardless of apical wall), and method C (apical approach: involvement of anterior septal and apical wall). Methods A and B gave a sensitivity of 100% each but a specificity of 47% and 56%, respectively. Although method C gave a higher value of specificity than that of methods A and B (98% vs 47% and 56%, respectively p < 0.05), the sensitivity of method C significantly decreased in respect to methods A and B (33% vs 100% p < 0.01). Isolated septal defects were evaluated separately. Isolated septal defects on exercise Tl-201 SPECT were detected in 11 patients, and none of them had CAD according to CAG results. Isolated septal wall involvement had a sensitivity of 0% and a specificity of 74%. The sensitivity and specificity of Tl-201 SPECT for diagnosis of CAD in the right coronary and left circumflex artery territories were 91% and 89%, respectively. In conclusion, the apical approach increased the specificity and decreased the sensitivity of the test. Isolated septal defects seem to have no value for diagnosis of CAD in patients with left bundle branch block.

Exercise-induced left bundle branch block during thallium 201 myocardial perfusion scintigraphy--a case report

Exercise-induced left bundle branch block (Ex-LBBB) is a rare entity encountered during exercise testing. The authors present a 53-year-old woman who developed intermittent Ex-LBBB asymptomatically during Tl 201 myocardial perfusion scintigraphy. Scintigraphic findings revealed septal-anteroseptal ischemia while the coronary arteriogram appeared normal. False-positive septal-anteroseptal scintigraphic findings suggesting ischemia in patients with persistent left bundle branch block (LBBB) is well known, but since the LBBB in this case was induced by exercise testing and was spontaneously terminated at rest, scintigraphic findings may be attributed to microcirculatory ischemia, which cannot be detected angiographically, as the cause of Ex-LBBB.

Mechanism for abnormal thallium-201 myocardial scintigraphy in patients with left bundle branch block in the absence of angiographic coronary artery disease

Patients with left bundle branch block (LBBB) often show abnormal images on exercise thallium (T1)-201 scintigraphy without evidence of significant coronary stenosis. We investigated the mechanism for this phenomenon. Six patients with LBBB and without significant coronary stenosis underwent T1-201 SPECT, ECG-gated SPECT imaging with Tc-99m-methoxyisobutyl-isonitrile (MIBI), and atrial pacing stress test. The % count amplitude in Tc-99m-MIBI images was calculated as [(maximal counts) - (minimal counts)]/(minimal counts) x 100. Though all patients had a low count in the septal and inferior wall in T1-201 SPECT images, there was no ischemic production of lactate during an atrial pacing stress test. Nevertheless, gated SPECT images showed attenuated septal activity during systole. In patients with LBBB, the ratios of % count amplitude at the septum to that at the lateral wall at rest (0.47 +/- 0.05, mean +/- SE) were significantly less than the controls (n = 5, 0.83 +/- 0.12, p = 0.014). In conclusion, these results suggest that abnormal T1-201 SPECT images of the septum in patients with LBBB are partially caused by impaired septal wall thickening during systole. Such an abnormal wall motion may reduce blood flow demands to the septum, resulting in reduction of coronary blood flow with little ischemia.

[Effectiveness of exercise echocardiography in the diagnosis of left bundle branch block. A case report]

A left bundle branch block is very often suggestive of cardiac diseases. Left bundle branch block is also present with angina in patients with normal coronary arteries. We report a case of a man with a left bundle branch block in which the most effective, rapid and economic method of diagnosis was exercise echocardiography. Different diagnostic techniques are discussed and compared.

[Role of noninvasive examinations in the management of ischemic cardiopathy. V. Noninvasive examinations in the management of patients with chronic ischemic cardiopathy]

In the last few years the has been an enormous development in noninvasive testing in the field of clinical cardiology. In fact, excellent monographs on each one of these techniques have been published elsewhere, but fewer publications exist that treat the topic of their indications and use in an integrated way, except for in the most common clinical situations. In this paper, the treatment of patients who present chest pain, stable and unstable angina is discussed, including the study of postinfarction patients. Furthermore, the role of noninvasive tests in the detection of coronary heart disease in women and in patients with left bundle branch block is thoroughly analyzed; as well as their usefulness after surgical or percutaneous coronary revascularization and in patients with peripheral vascular disease.

Myocardial viability: nuclear medicine versus stress echocardiography

The failure of nonimaging techniques in the identification of myocardial viability has promoted the clinical application of radioisotopic and echocardiographic methods. Unfortunately, none of these techniques provides, per se, a 100% predictive accuracy and only few studies have been based on the postoperative improvement in regional wall motion, the absolute "gold standard" for myocardial viability. The recent thallium-201 protocols (reinjection, late redistribution, rest studies) have provided nuclear cardiology with a cell membrane integrity image able to unmask viable myocardium in more than 85% of viable segments. Sestamibi has been introduced as a nonrecirculating flow tracer able to detect transient ischemia as well as thallium-201. Its main limit, a high sensitivity to intermediate reductions in coronary blood flow, determines a high incidence of false positive studies. Positron emission tomography allows the evaluation of regional myocardial blood flow and metabolism. The marker of viable myocardium is the mismatch between reduced blood flow and normal or increased uptake of 18-F fluorodeoxyglucose. This technique allows the detection of viable tissue in most segments showing improved postoperative function. In our experience, applying a multiparametric approach, rest thallium-201 scan, rest sestamibi, dobutamine, and dipyridamole echocardiography showed a sensitivity and a specificity of 86%, 75%, 82%, 75% and 92%, 84%, 92%, and 89%, respectively, in the detection of residual viability. The main advantages of thallium-201 are reproducibility and standardization; those of stress echo are low cost and availability. In patients with severely depressed ventricular function, positron emission tomography retains a primary role when compared to thallium-201 and stress echocardiography.