Coronary sinus filling time: a novel method to assess microcirculatory function in patients with angina and normal coronaries

"Myocardial transit-time" (MyoTT): a novel and easy-to-perform CMR parameter to assess microvascular disease

BACKGROUND

Myocardial microvascular disease may occur during the disease course of different cardiac as well as systemic disorders. With the present study, we introduce a novel and easy-to-perform cardiovascular magnetic resonance (CMR) parameter named "myocardial transit-time" (MyoTT).

METHODS

N = 20 patients with known hypertrophic cardiomyopathy (HCM) and N = 20 control patients without relevant cardiac disease underwent dedicated CMR studies on a 1.5-T MR scanner. The CMR protocol comprised cine and late-gadolinium-enhancement (LGE) imaging as well as first-pass perfusion acquisitions at rest for MyoTT measurement. MyoTT was defined as the blood circulation time from the orifice of the coronary arteries to the pooling in the coronary sinus (CS), and accordingly measured as the temporal difference between the appearances of CMR contrast agent in the aortic root and the CS reflecting the transit-time of gadolinium in the myocardial microvasculature.

RESULTS

Patients with HCM had a significantly prolonged MyoTT compared to controls (11.0 (9.1-14.5) s vs. 6.5 (4.8-8.4) s, p < 0.001). This significant difference did not change when the individual heart rate was taken into consideration (MyoTT indexed, p < 0.001). Significant correlations were found between MyoTT and maximal left ventricular (LV) wall thickness (r = 0.771, p < 0.001), MyoTT and presence of LGE (r = 0.760, p < 0.001) as well as MyoTT and LV global longitudinal strain (r = 0.672, p < 0.001). ROC analysis resulted in an area-under-curve (AUC) of 0.90 for MyoTT and showed an optimal sensitivity/specificity cut-off of 7.85 s to differentiate HCM from controls.

CONCLUSION

"Myocardial transit-time" is a novel and easy-to-perform CMR parameter that allows a quick assessment of the extent of myocardial microvascular disease. This novel CMR parameter may open new vistas in the assessment of microvascular disease-not only in HCM patients. Future studies will show the usefulness and clinical relevance of this novel CMR parameter.

Assessing and managing coronary microcirculation dysfunction in acute ST-segment elevation myocardial infarction

INTRODUCTION

Microvascular dysfunction in the setting of acute ST-segment elevation myocardial infarction (STEMI) is an indicator of poor long-term prognosis. Prompt assessment and pharmacological or procedural therapy (prophylactic or post onset of dysfunction) may improve outcomes in STEMI post-primary percutaneous intervention. Areas covered: The aim of this review is to provide a comprehensive analysis of the evidence available about the assessment and management of coronary microcirculatory injury/dysfunction in STEMI. We also aim to elucidate the possible strategies that could be applied in clinical practice to support the application of already available or novel therapeutic strategies for the prevention and management of microvascular impairment. Expert commentary: There are multiple established methods in assessing microvascular dysfunction, both non-invasively and invasively. Invasive physiological measurements allow real-time assessment of microvascular dysfunction and have prognostic cut-off values. Multiple therapeutic modalities exist for both preventing and treating microvascular dysfunction. These can be either pharmacological or mechanical, and there is no algorithm to guide if, how and when to apply them. Future research into both procedural and pharmacological therapy guided by physiological measurements is needed, with the aim of recognizing high-risk patients who would benefit from therapy.

Evaluation of the coronary flow by the coronary clearance time in patients with cardiac syndrome X

Objective

The vessels involved in the microcirculation are too small to be visualized by conventional angiography and no tools are currently available that can directly evaluate the coronary microcirculation. This study evaluated the coronary clearance frame count (CCFC) in patients with cardiac syndrome X (CSX).

Methods

The retrospective study enrolled patients with angina, who had a positive nuclear imaging test and normal coronary angiography; and a control group consisting of patients who underwent an angiogram to exclude coronary artery disease. Thrombosis in myocardial infarction frame count (TFC) and CCFC for each coronary artery (left anterior descending coronary artery [LAD], circumflex coronary artery [CFX] and right coronary artery [RCA]) were calculated offline.

Results

A total of 71 patients with CSX and 61 control patients were enrolled in the study. No significant differences were found between the two groups regarding the baseline demographic and clinical variables. The TFC of LAD, CFX and RCA were similar between the two groups. The mean CCFC-LAD, CCFC-CFX and CCFC-RCA were significantly longer in the CSX group compared with the control group.

Conclusion

CCFC is a simple, quantitative and highly reproducible method that might be used as a marker of coronary microvascular dysfunction.

Functional Assessment of Coronary Artery Disease Using Whole-Heart Dynamic Computed Tomographic Perfusion

BACKGROUND

Computed tomographic (CT) angiography is an important tool for the evaluation of coronary artery disease but often correlates poorly with myocardial ischemia. Current dynamic CT perfusion techniques can assess ischemia but have limited accuracy and deliver high radiation dose. Therefore, an accurate, low-dose, dynamic CT perfusion technique is needed.

METHODS AND RESULTS

A total of 20 contrast-enhanced CT volume scans were acquired in 5 swine (40±10 kg) to generate CT angiography and perfusion images. Varying degrees of stenosis were induced using a balloon catheter in the proximal left anterior descending coronary artery, and a pressure wire was used for reference fractional flow reserve (FFR) measurement. Perfusion measurements were made with only 2 volume scans using a new first-pass analysis (FPA) technique and with 20 volume scans using an existing maximum slope model (MSM) technique. Perfusion (P) and FFR measurements were related by P_FPA=1.01 FFR-0.03 (R²=0.85) and P_MSM=1.03 FFR-0.03 (R²=0.80) for FPA and MSM techniques, respectively. Additionally, the effective radiation doses were calculated to be 2.64 and 26.4 mSv for FPA and MSM techniques, respectively.

CONCLUSIONS

A new FPA-based dynamic CT perfusion technique was validated in a swine animal model. The results indicate that the FPA technique can potentially be used for improved anatomical and functional assessment of coronary artery disease at a relatively low radiation dose.

Dynamic CT perfusion measurement in a cardiac phantom

Widespread clinical implementation of dynamic CT myocardial perfusion has been hampered by its limited accuracy and high radiation dose. The purpose of this study was to evaluate the accuracy and radiation dose reduction of a dynamic CT myocardial perfusion technique based on first pass analysis (FPA). To test the FPA technique, a pulsatile pump was used to generate known perfusion rates in a range of 0.96-2.49 mL/min/g. All the known perfusion rates were determined using an ultrasonic flow probe and the known mass of the perfusion volume. FPA and maximum slope model (MSM) perfusion rates were measured using volume scans acquired from a 320-slice CT scanner, and then compared to the known perfusion rates. The measured perfusion using FPA (P(FPA)), with two volume scans, and the maximum slope model (P(MSM)) were related to known perfusion (P(K)) by P(FPA) = 0.91P(K) + 0.06 (r = 0.98) and P(MSM) = 0.25P(K) - 0.02 (r = 0.96), respectively. The standard error of estimate for the FPA technique, using two volume scans, and the MSM was 0.14 and 0.30 mL/min/g, respectively. The estimated radiation dose required for the FPA technique with two volume scans and the MSM was 2.6 and 11.7-17.5 mSv, respectively. Therefore, the FPA technique can yield accurate perfusion measurements using as few as two volume scans, corresponding to approximately a factor of four reductions in radiation dose as compared with the currently available MSM. In conclusion, the results of the study indicate that the FPA technique can make accurate dynamic CT perfusion measurements over a range of clinically relevant perfusion rates, while substantially reducing radiation dose, as compared to currently available dynamic CT perfusion techniques.

Prognostic significance of coronary sinus filling time in patients with angina and normal coronaries at one year follow up

BACKGROUND

Coronary sinus filling time (CSFT) has been proposed as a simple method for assessment of coronary microvascular function in patients with angina and normal coronaries. But its correlation with inducible ischemia and prognostic significance in predicting future cardiovascular events has not been studied. The present study assessed the prognostic significance of CSFT during one year of follow up.

METHODS

We compared coronary sinus filling time of patients with angina and normal coronaries with that of control population. Control group was formed by those patients with supraventricular arrhythmia undergoing radiofrequency ablation and having normal coronaries. Baseline treadmill test (TMT) parameters like workload, duration and Duke Score were assessed. Patients were followed up for one year and a composite of cardiovascular mortality and non-fatal myocardial infarction was analyzed. Number of patients presenting to emergency or outpatient department with recurrent chest pain symptoms during one year follow up was considered for secondary outcome analysis. Coronary sinus filling time was analyzed with respect to cardiovascular events, repeat hospitalization for recurrent angina and TMT parameters.

RESULTS

Total 72 patients and 16 controls were studied. Mean CSFT value in the study group was 5.31 ± 1.03 sec and in the control group was 4.16 ± 0.72 sec and the difference was significant (p value = 0.0001). No correlation was found between baseline and repeat TMT parameters with CSFT. There was no cardiovascular mortality or hospitalization for non-fatal MI during one year follow up. But patients with frequent emergency or outpatient department visits with chest pain had a high CSFT compared with asymptomatic patients (p value = 0.005).

CONCLUSION

Coronary sinus filling time may be used as a simple marker of microvascular dysfunction in patients with angina and normal coronaries. Patients with recurrent chest pain symptoms after one year follow up were found to have high CSFT compared to asymptomatic patients.