Adenosine triphosphate (ATP) and adenosine cause similar vasodilator effect in patients undergoing stress perfusion cardiac magnetic resonance imaging

Purinergic system in cancer stem cells

Accumulating evidence supports the idea that cancer stem cells (CSCs) are those with the capacity to initiate tumors, generate phenotypical diversity, sustain growth, confer drug resistance, and orchestrate the spread of tumor cells. It is still controversial whether CSCs originate from normal stem cells residing in the tissue or cancer cells from the tumor bulk that have dedifferentiated to acquire stem-like characteristics. Although CSCs have been pointed out as key drivers in cancer, knowledge regarding their physiology is still blurry; thus, research focusing on CSCs is essential to designing novel and more effective therapeutics. The purinergic system has emerged as an important autocrine-paracrine messenger system with a prominent role at multiple levels of the tumor microenvironment, where it regulates cellular aspects of the tumors themselves and the stromal and immune systems. Recent findings have shown that purinergic signaling also participates in regulating the CSC phenotype. Here, we discuss updated information regarding CSCs in the purinergic system and present evidence supporting the idea that elements of the purinergic system expressed by this subpopulation of the tumor represent attractive pharmacological targets for proposing innovative anti-cancer therapies.

Safety, feasibility, and hemodynamic response of regadenoson for stress perfusion CMR

Owing to its pharmacodynamics and posology, the use of regadenoson for stress cardiac magnetic resonance (CMR) has potential advantages over other vasodilators. We sought to evaluate the safety, hemodynamic response and diagnostic performance of regadenoson stress-CMR in routine clinical practice. All regadenoson stress-CMR examinations performed between May 2017 and July 2020 at our institution were retrospectively reviewed. A total of 698 studies were included for the final analysis. A conventional stress/rest protocol was performed using a 1.5T MRI scanner (Magnetom Aera, Siemens Healthineers, Erlangen, Germany). Adverse events, clinical symptoms, and hemodynamic response were assessed. Diagnostic accuracy of the test was evaluated in patients who underwent invasive coronary angiography. Nearly half of patients (48.5%) remained asymptomatic. Most common clinical symptoms included dyspnea (137, 19.6%), chest pain (116, 16.6%) and flushing (44, 6.3%). Two patients (0.28%) could not complete the examination due to severe hypotension or unbearable chest pain. Overall, an increase in heart rate (HR) response (36.2% [IQR: 22.5?50.9]) and a decrease in systolic and diastolic blood pressure (BP) (median systolic BP response of -5% [IQR: -11.5-0.6]; median diastolic BP response of -6.3 mmHg [IQR: -13.4-0]) was observed. Patients with symptoms induced by regadenoson showed higher HR response (40.3%, IQR: 26.4?56.1 vs. 32.4%, IQR: 19-45.6, p < 0.001), whereas a blunted HR response was observed in diabetic (29.6%, IQR: 18.4?42 p < 0.001), obese (31.7%, IQR: 20.7?46.2 p = 0.005) and patients aged 70 years or older (32.9%, IQR: 22.6?43.1 p < 0.001). Overall, regadenoson stress-CMR showed 95.65% (IQ 91.49?99.81) sensitivity, 54.84% (IQ 35.71?73.97) specificity, 86.99% (IQ 82.74?94.68) positive predictive value, and 77.27% (IQ 57.49?97.06) negative predictive value for detecting significant coronary stenosis as compared with invasive coronary angiography. Regadenoson is a well-tolerated vasodilator that can be safely employed for stress perfusion CMR, with high diagnostic performance.

Adenosine triphosphate (ATP): a safe and effective vasodilator for stress perfusion cardiac magnetic resonance imaging

AIM

To evaluate the efficiency and safety of adenosine triphosphate (ATP) as a stress agent in a cohort of patients undergoing stress perfusion cardiac magnetic resonance imaging (CMRI).

MATERIALS AND METHODS

This retrospective study was conducted between December 2019 and October 2021. The study recruited patients who underwent stress perfusion CMRI using ATP as a vasodilator. Adverse events, such as chest pain, flushing, dyspnoea, headache, and splenic switch-off (SSO) phenomenon, were evaluated in the patients who underwent stress perfusion CMRI.

RESULTS

The study included 107 patients (age range: 53 ± 11 years; male:female, 62%:38%). The haemodynamic response (heart rate increased by ≥ 10 beats/min) was quick and observed within 2 minutes of ATP infusion. Scanning was stopped in three patients because of atrioventricular block. CMRI images of seven out of 104 patients were excluded from the final analysis because of inferior quality. During ATP infusion, 37/107 patients (35%) experienced mild adverse events, such as chest pain, flushing, dyspnoea, headache, and atrioventricular block. Myocardial infarction and bronchospasms were not observed during ATP infusion. SSO, a marker of adequate stress, was observed in 91% (94/103) of the patients who underwent stress perfusion CMRI.

CONCLUSIONS

As a coronary vasodilator, ATP was safe for stress perfusion CMRI. In addition, the adverse events during ATP infusion were mild, which were relieved within 2 minutes of ATP injection cessation. SSO could serve as an indicator of stress success in ATP stress perfusion CMRI.

Qualitative and Quantitative Stress Perfusion Cardiac Magnetic Resonance in Clinical Practice: A Comprehensive Review

Stress cardiovascular magnetic resonance (CMR) imaging is a well-validated non-invasive stress test to diagnose significant coronary artery disease (CAD), with higher diagnostic accuracy than other common functional imaging modalities. One-stop assessment of myocardial ischemia, cardiac function, and myocardial viability qualitatively and quantitatively has been proven to be a cost-effective method in clinical practice for CAD evaluation. Beyond diagnosis, stress CMR also provides prognostic information and guides coronary revascularisation. In addition to CAD, there is a large body of literature demonstrating CMR's diagnostic performance and prognostic value in other common cardiovascular diseases (CVDs), especially coronary microvascular dysfunction (CMD). This review focuses on the clinical applications of stress CMR, including stress CMR scanning methods, practical interpretation of stress CMR images, and clinical utility of stress CMR in a setting of CVDs with possible myocardial ischemia.

Advances in Myocardial Perfusion MR Imaging: Physiological Implications, the Importance of Quantitative Analysis, and Impact on Patient Care in Coronary Artery Disease

Stress myocardial perfusion imaging (MPI) is the preferred test in patients with intermediate-to-high clinical likelihood of coronary artery disease (CAD) and can be used as a gatekeeper to avoid unnecessary revascularization. Cardiac magnetic resonance (CMR) has a number of favorable characteristics, including: (1) high spatial resolution that can delineate subendocardial ischemia; (2) comprehensive assessment of morphology, global and regional cardiac functions, tissue characterization, and coronary artery stenosis; and (3) no radiation exposure to patients. According to meta-analysis studies, the diagnostic accuracy of perfusion CMR is comparable to positron emission tomography (PET) and perfusion CT, and is better than single-photon emission CT (SPECT) when fractional flow reserve (FFR) is used as a reference standard. In addition, stress CMR has an excellent prognostic value. One meta-analysis study demonstrated the annual event rate of cardiovascular death or non-fatal myocardial infarction was 4.9% and 0.8%, respectively, in patients with positive and negative stress CMR. Quantitative assessment of perfusion CMR not only allows the objective evaluation of regional ischemia but also provides insights into the pathophysiology of microvascular disease and diffuse subclinical atherosclerosis. For accurate quantification of myocardial perfusion, saturation correction of arterial input function is important. There are two major approaches for saturation correction, one is a dual-bolus method and the other is a dual-sequence method. Absolute quantitative mapping with myocardial perfusion CMR has good accuracy in detecting coronary microvascular dysfunction. Flow measurement in the coronary sinus (CS) with phase contrast cine CMR is an alternative approach to quantify global coronary flow reserve (CFR). The measurement of global CFR by quantitative analysis of perfusion CMR or flow measurement in the CS permits assessment of microvascular disease and diffuse subclinical atherosclerosis, which may provide improved prediction of future event risk in patients with suspected or known CAD. Multi-institutional studies to validate the diagnostic and prognostic values of quantitative perfusion CMR approaches are required.

Prognostic value of perfusion cardiovascular magnetic resonance with adenosine triphosphate stress in stable coronary artery disease

BACKGROUND

Adenosine triphosphate (ATP) has been predominantly used in the Asia-Pacific region for stress perfusion cardiovascular magnetic resonance (CMR). We evaluated the prognosis of patients stressed using ATP, for which there are no current data.

METHODS

We performed a retrospective longitudinal study from January 2016 to December 2020 and included 208 subjects with suspected obstructive coronary artery disease (CAD) who underwent ATP stress perfusion CMR. An inducible stress perfusion defect was defined as a subendocardial dark rim involving ≥ 1.5 segments that persisted for ≥ 6 beats during stress but not at rest. The primary outcome measure was a composite of major adverse cardiovascular events (MACE) including (1) cardiac death, (2) nonfatal myocardial infarction, (3) cardiac hospitalization, (4) late coronary revascularization. We compared outcomes in patients with and without perfusion defect using Kaplan-Meier and log rank tests. Significant predictors of MACE were identified using multivariable Cox regression analysis.

RESULTS

Median follow-up was 3.3 years. Patients with no stress perfusion defect had a lower incidence of MACE (p < 0.001), including lower cardiac hospitalization (p = 0.004), late coronary revascularization (p = 0.001) and cardiac death (p = 0.003). Significant independent predictors for MACE were stress induced perfusion defect (p < 0.001, hazard ratio [HR] = 3.63), lower left ventricular ejection fractino (LVEF) (p < 0.001, HR = 0.96) and infarct detected by late gadolinium enhancement (LGE) (p = 0.001, HR = 2.92).

CONCLUSION

Perfusion defects on ATP stress are predictive of MACE which is driven primarily by cardiac hospitalization, late coronary revascularization and cardiac death. Significant independent predictors of MACE were stress induced perfusion defect, lower LVEF and infarct detected by LGE.

Long-Term Prognosis of Patients With Coronary Microvascular Disease Using Stress Perfusion Cardiac Magnetic Resonance

OBJECTIVES

This study investigated the prognosis of coronary microvascular disease (CMD) as determined by stress perfusion cardiac magnetic resonance (CMR) in patients with ischemic symptoms but without significant coronary artery disease (CAD).

BACKGROUND

Patients with CMD have poorer prognosis with various cardiac diseases. The myocardial perfusion reserve index (MPRI) derived from noninvasive stress perfusion CMR has been established to diagnose microvascular angina with a threshold MPRI <1.4. The prognosis of CMD as determined by MPRI is unknown.

METHODS

Chest pain patients without epicardial CAD or myocardial disease from January 2009 to December 2017 were retrospectively included from 3 imaging centers in Hong Kong (HK). Stress perfusion CMR examinations were performed using either adenosine or adenosine triphosphate. Adequate stress was assessed by achieving splenic switch-off sign. Measurement of MPRI was performed in all stress perfusion CMR scans. Patients were followed for major adverse cardiovascular events defined as all-cause death, acute coronary syndrome (ACS), epicardial CAD development, heart failure hospitalization and non-fatal stroke.

RESULTS

A total of 218 patients were studied (mean age 59 ± 12 years; 49.5% male) and the average MPRI of that cohort was 1.56 ± 0.33. Females and a history of hyperlipidemia were predictors of lower MPRI. Major adverse cardiovascular events (MACE) occurred in 15.6% of patients during a median follow-up of 5.5 years (interquartile range: 4.6 to 6.8 years). The optimal cutoff value of MPRI in predicting MACE was found with a threshold MPRI ≤1.47. Patients with MPRI ≤1.47 had three-fold increased risk of MACE compared with those with MPRI >1.47 (hazard ratio [HR]: 3.14; 95% confidence interval [CI]: 1.58 to 6.25; p = 0.001). Multivariate Cox regression after adjusting for age and hypertension demonstrated that MPRI was an independent predictor of MACE (HR: 0.10; 95% CI: 0.03 to 0.34; p < 0.001).

CONCLUSIONS

Stress perfusion CMR-derived MPRI is an independent imaging marker that predicts MACE in patients with ischemic symptom and no overt CAD over the medium term.

Diagnostic performance of quantitative, semi-quantitative, and visual analysis of dynamic CT myocardial perfusion imaging: a validation study with invasive fractional flow reserve

OBJECTIVES

To investigate the diagnostic performance of absolute myocardial blood flow (MBF), MBF_ratio, and visual analysis of dynamic CT myocardial perfusion imaging (CT-MPI) for the detection of hemodynamically significant coronary stenosis.

METHODS

Consecutive patients with chest pain and intermediate-to-high pre-test probability of obstructive coronary artery disease were prospectively enrolled. All patients were referred for dynamic CT-MPI and fractional flow reserve (FFR) measurements within 4 weeks. Absolute MBF, MBF_ratio (mean MBF of stenosis-subtended territories versus that of reference territories), and visually identified perfusion defect were tested for the diagnostic performance with reference to FFR.

RESULTS

Sixty-two patients with 95 target vessels were included for final analysis. The mean radiation dose for dynamic CT-MPI was 3.0 (2.2-4.0) mSv. The mean lesion-based absolute MBF value was significantly lower in ischemic segments than that in non-ischemic segments (78.0 (65.0-86.0) mL/min/100 mL vs. 133.0 (117.5-163.8) mL/min/100 mL, p < 0.001). Similarly, the lesion-based MBF_ratio was also markedly lower in territories with positive FFR results (0.52 (0.44-0.64) vs. 0.93 (0.91-0.97), p < 0.001). According to per-lesion ROC curve analysis, MBF and MBF_ratio had a similar area under the curve (AUC) for detecting hemodynamically significant lesions (AUC = 0.942 vs. 0.956, p = 0.413), which were larger than that of visual analysis (AUC = 0.802, both p < 0.01). The vessel-based sensitivity, specificity, and diagnostic accuracy were 84.3%, 97.7%, and 90.5% for MBF and 96.1%, 93.2%, and 94.7% for MBF_ratio.

CONCLUSIONS

Absolute MBF and MBF_ratio had similarly excellent diagnostic performance with reference to FFR. In addition, these two parameters outperformed visual analysis for the detection of myocardial ischemia.

KEY POINTS

• The mean MBF and MBF_ratio were significantly lower in ischemic segments than those in non-ischemic segments. • Absolute MBF and MBF_ratio had similar AUCs for the detection of hemodynamically significant lesions (AUC = 0.942 vs. 0.956, p = 0.413), which were larger than that of visual analysis (AUC = 0.802, both p < 0.01). • The vessel-based sensitivity, specificity, and diagnostic accuracy were 84.3%, 97.7%, and 90.5% for absolute MBF and 96.1%, 93.2%, and 94.7% for MBF_ratio.

Impact of caffeine on myocardial perfusion reserve assessed by semiquantitative adenosine stress perfusion cardiovascular magnetic resonance

BACKGROUND

Adenosine is used in stress perfusion cardiac imaging to reveal myocardial ischemia by its vasodilator effects. Caffeine is a competitive antagonist of adenosine. However, previous studies reported inconsistent results about the influence of caffeine on adenosine's vasodilator effect. This study assessed the impact of caffeine on the myocardial perfusion reserve index (MPRI) using adenosine stress cardiovascular magnetic resonance imaging (CMR). Moreover, we sought to evaluate if the splenic switch-off sign might be indicative of prior caffeine consumption.

METHODS

Semiquantitative perfusion analysis was performed in 25 patients who underwent: 1) caffeine-naïve adenosine stress CMR demonstrating myocardial ischemia and, 2) repeat adenosine stress CMR after intake of caffeine. MPRI (global; remote and ischemic segments), and splenic perfusion ratio (SPR) were assessed and compared between both exams.

RESULTS

Global MPRI after caffeine was lower vs. caffeine-naïve conditions (1.09 ± 0.19 vs. 1.24 ± 0.19; p <  0.01). MPRI in remote myocardium decreased by caffeine (1.24 ± 0.19 vs. 1.49 ± 0.19; p <  0.001) whereas MPRI in ischemic segments (0.89 ± 0.18 vs. 0.95 ± 0.23; p = 0.23) was similar, resulting in a lower MPRI ratio (=remote/ischemic segments) after caffeine consumption vs. caffeine-naïve conditions (1.41 ± 0.19 vs. 1.64 ± 0.35, p = 0.01). The SPR was unaffected by caffeine (SPR 0.38 ± 0.19 vs. 0.38 ± 0.18; p = 0.92).

CONCLUSION

Caffeine consumption prior to adenosine stress CMR results in a lower global MPRI, which is driven by the decreased MPRI in remote myocardium and underlines the need of abstinence from caffeine. The splenic switch-off sign is not affected by prior caffeine intake.