Dipyridamole TI-201 SPECT imaging in patients with myocardial bridging

Case report: A fatal case of myocardial infarction due to myocardial bridge and concomitant vasospasm: the role of stress gated SPECT

Introduction

Although most cases of myocardial bridge (MB) are clinically benign, sometimes it can be one of potential threats of myocardial infarction (MI) and life-threatening arrhythmia. In the present study, we present a case of ST-segment elevation MI caused by MB and concomitant vasospasm.

Case Presentation

A 52-year-old woman was brought to our tertiary hospital due to resuscitated cardiac arrest. Because the 12-lead electrocardiogram indicated ST-segment elevation MI, coronary angiogram was promptly commenced, which showed near-total occlusion at the middle portion of left anterior descending coronary artery (LAD). After intracoronary nitroglycerin administration, this occlusion was dramatically relieved, however, systolic compression at this site remained, indicative of myocardial bridge (MB). Intravascular ultrasound also showed eccentric compression with a "half-moon" sign, which is consistent with MB. Coronary computed tomography also showed a bridged coronary segment surrounded by myocardium at the middle portion of LAD. To assess the severity and extent of myocardial damages and ischemia, myocardial single photon emission computed tomography (SPECT) was additionally conducted, showing a moderate fixed perfusion defect around the cardiac apex, suggesting MI. After receiving optimal medical therapy, the patient's clinical symptoms and signs were improved then the patient was discharged from the hospital successfully and uneventfully.

Conclusion

We demonstrated a case of MB-induced ST-segment elevation MI which was confirmed with its perfusion defects via myocardial perfusion SPECT. There have been proposed a number of diagnostic modalities to examine its anatomic and physiologic significance. Among them, myocardial perfusion SPECT can be available as one of useful modalities to evaluate the severity and extent of myocardial ischemia in patients with MB.

The Myocardial Bridge: Potential Influences on the Coronary Artery Vasculature

A myocardial bridge (MB) is an anatomical abnormality of the coronary artery and is characterized by the systolic narrowing of the epicardial coronary artery caused by myocardial compression during systole. An MB is frequently observed on cardiac computed tomography or coronary angiography and generally appears to be harmless in the majority of patients. However, the presence of MB is reportedly associated with abnormalities of the cardiovascular system, including coronary artery diseases, arrhythmia, certain types of cardiomyopathy, and cardiac death, indicating that MB serves a pivotal role in the occurrence and/or development of such cardiovascular events. Recently, there has been an increasing interest in the coexistence of MB and coronary spasm in research due to opposing aspects regarding their treatments. For example, monotherapy using β-blockers, which are effective in patients with MB, may worsen symptoms in patients with coronary spasm. By contrast, nitroglycerin, which is an effective treatment option for coronary spasm, may worsen symptoms in patients with MB. This review focuses on the pathophysiology and diagnosis of MB and MB-related cardiovascular diseases, including coronary spasm, and on the treatment strategies for MB.

Assessment of Myocardial Bridge by Cardiac CT: Intracoronary Transluminal Attenuation Gradient Derived from Diastolic Phase Predicts Systolic Compression

Objective

To study the predictive value of transluminal attenuation gradient (TAG) derived from diastolic phase of coronary computed tomography angiography (CCTA) for identifying systolic compression of myocardial bridge (MB).

Materials and Methods

Consecutive patients diagnosed with MB based on CCTA findings and without obstructive coronary artery disease were retrospectively enrolled. In total, 143 patients with 144 MBs were included in the study. Patients were classified into three groups: without systolic compression, with systolic compression < 50%, and with systolic compression ≥ 50%. TAG was defined as the linear regression coefficient between intraluminal attenuation in Hounsfield units (HU) and length from the vessel ostium. Other indices such as the length and depth of the MB were also recorded.

Results

TAG was the lowest in MB patients with systolic compression ≥ 50% (-19.9 ± 8.7 HU/10 mm). Receiver operating characteristic curve analysis was performed to determine the optimal cutoff values for identifying systolic compression ≥ 50%. The result indicated an optimal cutoff value of TAG as -18.8 HU/10 mm (area under curve = 0.778, p < 0.001), which yielded higher sensitivity, specificity, positive predictive value, negative predictive value, and diagnostic accuracy (54.1, 80.5, 72.8, and 75.0%, respectively). In addition, the TAG of MB with diastolic compression was significantly lower than the TAG of MB without diastolic compression (-21.4 ± 4.8 HU/10 mm vs. -12.7 ± 8 HU/10 mm, p < 0.001).

Conclusion

TAG was a better predictor of MB with systolic compression ≥ 50%, compared to the length or depth of the MB. The TAG of MB with persistent diastolic compression was significantly lower than the TAG without diastolic compression.

Role of 99mTc-sestamibi gated SPECT/CT myocardial perfusion imaging in the management of patients with myocardial bridging and its correlation with coronary angiography

Myocardial bridging (MB)-a congenital coronary abnormality in its severe form leads to myocardial edema, fibrosis, and ischemia due to coronary artery compression during systole and early part of the diastole. This study evaluated the hemodynamic significance of MB by detecting severity and extent of perfusion abnormality using ^99mTc-sestamibi (MIBI) gated single photon emission computed tomography (SPECT)/CT myocardial perfusion imaging (MPI), its correlation with coronary angiography and role in patient's management. Five patients with complaints of atypical chest pain, exertional angina, or dyspnea underwent stress/rest ^99mTc-MIBI SPECT/CT MPI. The gated stress and rest SPECT/CT images on 17 segment model using quantitative gated-SPECT (QGS) softwarewere analyzed and compared with coronary angiography. Four out of five patients showed reversible perfusion defect in the left anterior descending (LAD) territory segments involved with myocardial bridging (3 patients had already proven MB; while MB was detected in 1 patient after MPI). The fifth patient with MB in the distal LAD revealed normal myocardial perfusion. All the patients were conservatively managed either due to small reversible perfusion defects or normal study except one patient. The gated SPECT/CT MPI of five patients with MB in the present study revealed their perfusion status, information on myocardial wall thickening, contractility, and ejection fraction. <Learning objective: Myocardial bridging may be one of the underlying causes for angina or sudden death even in absence of cardiovascular risk factors. The proven or clinical suspicious myocardial bridging in patients with typical/atypical chest pain and low probability of atherosclerosis should be evaluated with gated SPECT/CTMPI. It helps in detection of coronary artery disease along with severity and extent of myocardial ischemia for their further management.>.

Multimodality Imaging in the Assessment of the Physiological Significance of Myocardial Bridging

In myocardial bridging (MB) a segment of the coronary artery is covered by the myocardium. MB can be seen as a systolic compression by invasive coronary angiography (ICA) or as an intramural course by computed tomography angiography (CTA). Intramural course is a common incidental finding in CTA studies. Only minority of the bridging segments are associated with systolic compression causing a possible impairment of myocardial perfusion. The relationship between myocardial blood flow and MB is complex and poorly evaluated by anatomic imaging. Furthermore, provocation tests are frequently needed to uncover systolic compression. Fractional flow reserve can be used to assess the hemodynamic significance of MB. Nuclear perfusion imaging can demonstrate flow abnormalities associated with MB. Stress echocardiography can demonstrate ischemic wall motion abnormalities. They can be complemented by hybrid imaging with CTA to distinguish epicardial coronary artery disease and MB. This article will review different imaging modalities for the evaluation of the physiologic significance of MB.

Myocardial bridging on coronary CTA: an innocent bystander or a culprit in myocardial infarction?

Myocardial bridging describes the clinical entity whereby a segment of coronary artery is either partially or completely covered by surrounding myocardium. It represents the most frequent congenital coronary anomaly and has an estimated prevalence of ≤13% on angiographic series. With the emergence of cardiac computed tomography and its ability to simultaneously image the coronary arteries and also the myocardium, there has been an apparent increase in the detection rates of myocardial bridges (prevalence as high as 44%). It has now become important to evaluate their clinical significance. Myocardial bridging is generally considered a benign entity with survival rates of 97% at 5 years; however, there is now emerging evidence that certain myocardial bridge characteristics may be associated with cardiovascular morbidity. The length and depth of myocardial bridges have been associated with increased atherosclerosis, whereas the degree of systolic compression has been associated with ischemia on myocardial perfusion single-photon emission tomography. On the basis of current evidence, it appears that limiting further testing for ischemia to symptomatic patients with long and/or deep myocardial brides would be appropriate.

(1) coronary events caused by myocardial bridge

Myocardial bridge (MB), which covers a part of the left anterior descending coronary artery (LAD), is a normal anatomical variant structure (45% in frequency by autopsy) in LAD. MB contraction plays the role of a "double-edged sword" on the coronary events, suppressing coronary atherosclerosis under the MB, yet generating abnormal blood flow associated with coronary heart diseases (CHDs). High shear stress driven by MB compression causes the suppression of vascular permeability and vasoactive protein expression such as e-NOS and endothelin-1, which leads to the suppression of atherosclerosis in the LAD segment under the MB. However, despite the prevalent view of MB as benignancy by conventional coronary angiography (5-6% in frequency), with advance of imaging technique such as multislice spiral computed tomography [(MSCT); 16% in frequency], cardiologists are now frequently aware of symptomatic MB occurring not only in hospitalized patients, but also in young athletes free from atherosclerosis. Moreover, the large mass volume of MB muscle induces atherosclerosis evolution at the settled site in LAD proximal to MB and contributes to the occurrence of myocardial infarction. These events upon the coronary events result from the different pathophysiological mechanisms induced by contractile force of MB, which is solely determined just by the integration of anatomical properties of MB, such as the location, length and thickness of MB in an individual LAD. A recent MSCT provides the objective quantification of the anatomical variables that correlate with the histopathological results in relation to the occurrence of CHD. In this review, we therefore discuss the necessity to explore MB as a inherent chance anatomical risk factor for CHD.

Myocardial bridging increases the risk of coronary spasm

BACKGROUND

Myocardial bridging (MB) has been associated with cardiac events. Whether coronary spasm is one factor contributing to those events is unknown.

HYPOTHESIS

This study investigated whether the likelihood of coronary spasm is increased in patients with MB.

METHODS

A spasm-provocation test was performed by infusing acetylcholine into the left coronary artery in 114 Japanese patients with chest pain. The test result was defined as positive when the diameter of the coronary artery was reduced by > or = 50% and ST-segment changes were documented. Myocardial bridging was defined as a > 15% reduction in coronary arterial diameter during systole after intracoronary injection of nitroglycerin.

RESULTS

Myocardial bridging was identified in 41 patients (36%) and was located in the mid-segment of the left anterior descending coronary artery (LAD) in all patients. Patients with MB experienced coronary spasm more frequently than patients without MB (MB+: 73%; MB-: 40%, p = 0.0006). Furthermore, among patients with a positive spasm-provocation test, coronary spasm occurred more frequently in the mid-segment of the LAD in patients with MB than in those without MB (MB+: 73%; MB-: 45%, p = 0.0259). Multivariate regression analysis demonstrated that MB was a predictor of coronary spasm (odds ratio: 3.478, p = 0.0088).

CONCLUSIONS

These results suggest that MB increases the risk of coronary spasm and that coronary spasm may be the proximate etiology of cardiac events associated with MB.

Myocardial bridging

Myocardial bridging, a congenital coronary anomaly, is a clinical condition with several possible manifestations, and its clinical relevance is debated. This article reviews current knowledge about the anatomy, pathophysiology, clinical relevance, and treatment of myocardial bridging. Myocardial bridging is present when a segment of a major epicardial coronary artery, the 'tunnelled artery', runs intramurally through the myocardium. With each systole, the coronary artery is compressed. Myocardial bridging has been associated with angina, arrhythmia, depressed left ventricular function, myocardial stunning, early death after cardiac transplantation, and sudden death. Evidence indicates that the intima beneath the bridge is protected from atherosclerosis, and the proximal segment is more susceptible to development of atherosclerotic lesions because of haemodynamic disturbances. New techniques (e.g. intravascular ultrasonography and intracoronary Doppler studies) have revealed new characteristics and pathophysiologic processes such as diastolic flow abnormalities. Medical treatment generally includes beta-blockers. Nitrates should be avoided because symptoms may worsen. Intracoronary stents and surgery have been attempted in selected patients. Additional research is needed to define patients in whom myocardial bridging is potentially pathologic, and randomized multicentre long-term follow-up studies are needed to assess the natural history, patient selection, and therapeutic approaches.