Continuous vs Bolus Thermodilution to Assess Microvascular Resistance Reserve

Invasive coronary function testing in clinical practice: Implementing the 2024 ESC guidelines on chronic coronary syndromes

Angina with non-obstructive coronary arteries (ANOCA) is increasingly recognized as a significant aspect of chronic coronary syndromes. These patients frequently experience recurrent angina, resulting in high healthcare costs and impaired quality of life. Invasive coronary function testing (ICFT) is able to identify ANOCA endotypes, which can guide treatment and improve quality of life. Despite Class II recommendations for invasive microvascular assessments in the previous 2019 European Society of Cardiology (ESC) Guidelines, ICFT has yet to translate into widespread clinical practice. Patients with ANOCA experience poor quality of life and reduced functional capacity, highlighting the need for earlier ICFT implementation. The 2024 ESC Guidelines now strongly recommend ICFT (Class I, level of evidence B) for patients with non-obstructive coronary arteries and persistent angina despite optimal medical therapy, and for confirming or excluding ANOCA in patients with uncertain diagnoses on non-invasive testing (Class I, level of evidence B). Consequently, a standardized approach to optimize the management of ANOCA patients is warranted. Therefore, this review aims to provide interventional cardiologists with a contemporary review of the literature and a practical guideline on implementation of ICFT. It will discuss the following subjects: the definitions of the different endotypes, an example of an ICFT protocol, discontinuation of medication prior to ICFT, use of radial cocktail, target vessel for testing, acetylcholine injection techniques and rechallenge, adenosine injection techniques, the order of testing, the interpretation of ICFT, safety and feasibility, and the pharmacological treatment.

Challenges in diagnosing coronary microvascular dysfunction and coronary vasospasm

Chronic coronary syndromes (CCS) include 2 overlapping subgroups of patients - those with angina with nonobstructive coronary arteries (ANOCA), or ischaemia with non-obstructive coronary arteries (INOCA). A diagnosis of ANOCA-INOCA, is common and should be considered where angina is present and/or ischaemia is found on functional imaging in the absence of obstructive coronary artery disease (CAD) on coronary computed tomography angiography (CCTA) or invasive coronary angiography (ICA) (Ford and Berry, 2019). This review aims to provide an overview of contemporary challenges in the diagnosis of coronary microvascular dysfunction (CMD) and vasospastic disease, with a focus on recent guideline changes and current controversies. CMD and vasospastic angina (VSA) are increasingly acknowledged as an important and frequently overlooked, under investigated, and undertreated entities that contribute to ANOCA-INOCA (Samuels et al., 2023; Kunadian et al., 2020; Ford and Berry, 2019; Burgess and Mamas, 2024).

Single-Center Analysis of Soluble TREM2 as a Biomarker in Coronary Microvascular Dysfunction: A Cross-Sectional Study

Background: The soluble triggering receptor expressed on myeloid cells 2 (sTREM2) is linked to the progression of cardiovascular conditions, but its role in coronary microcirculation dysfunction (CMD) is not yet clear. Methods: A cross-sectional observational study from July 2023 to May 2024 was conducted in the China-Japan Friendship Hospital, after registration in the ClinicalTrials database (Registry Name: Coronary Microvascular Dysfunction in Angina Patients With Non-obstructive Coronary Artery Disease (ANOCA-CMD); Registry Number: NCT06503640; Registry Date: 23 September 2022). This cross-sectional study involved 76 subjects, including 55 patients with CMD and 21 without CMD, admitted to the China-Japan Friendship Hospital. CMD was defined by a coronary flow reserve (CFR) < 2.5 or index of microvascular resistance (IMR) ≥ 25. sTREM2 levels were measured using an enzyme-linked immunosorbent assay. Linear correlation analysis assessed the relationship between sTREM2 levels and CFR, IMR, microvascular resistance reserve (MRR), and the resistive reserve ratio (RRR). Univariate and multivariate regression analyses further examined the association between sTREM2 and CMD. Additionally, receiver operating characteristic (ROC) analysis was used to evaluate the diagnostic accuracy of plasma sTREM2 for identifying CMD patients. Results: Elevated sTREM2 levels were found in the CMD group. Correlation analysis showed a significant positive relationship with IMR and an inverse correlation with CFR, MRR, and RRR. After adjusting for confounders, sTREM2 was found to be an independent risk factor for CMD [OR = 1.003, 95% CI 1.001-1.007, p = 0.008]. ROC analysis revealed a sensitivity of 59.46%, specificity of 90.48%, and an AUC of 0.7677 (95% CI: 0.6481-0.8872, p = 0.008) for CMD diagnosis at a threshold of 595.5 pg/mL, indicating good diagnostic performance. Conclusions: Elevated sTREM2 levels in CMD patients indicate its potential as a biomarker.

Ischemia with no obstructed coronary arteries and microvascular testing procedures: a review of utility, pharmacotherapy, and current challenges

Ischemia with no obstructive coronary arteries (INOCA) is an increasingly recognized condition in patients presenting with angina and positive stress tests but without significant coronary artery stenosis. This review addresses the pathophysiology, diagnostic approaches, and management strategies associated with INOCA, emphasizing epicardial coronary spasms and coronary microvascular dysfunction (CMD) as underlying mechanisms and myocardial bridging (MB) as a risk factor. Diagnostic modalities include both non-invasive techniques and invasive procedures, such as acetylcholine provocation testing, to differentiate vasospasm from microvascular causes. The paper discusses a potential interference between vasodilators used in trans-radial access and coronary spasm testing. Long-term management approaches for INOCA patients, including pharmacologic therapies and lifestyle interventions, are reviewed.

The role of non-invasive stress testing in the diagnosis of coronary microvascular disease

BACKGROUND

Angina with non-obstructive coronary artery disease (ANOCA) is commonly observed in patients with stable angina undergoing coronary angiography. Current guidelines recommend non-invasive stress testing as the first step in diagnosing coronary microvascular disease (CMD). This study aims to evaluate the diagnostic value of non-invasive stress testing in patients invasively diagnosed with CMD.

METHODS

We conducted a retrospective analysis of prospectively collected data. Eligible subjects were patients with angina who underwent NIST evaluation (echocardiography/ electrocardiography stress test or single-photon emission computerized tomography) prior to coronary angiography. All patients underwent invasive evaluation of microvascular function, which included the assessment of Coronary Flow Reserve, Index of Microcirculatory Resistance, and Resistive Reserve Ratio.

RESULTS

Overall, 140 patients (77 women, 67 ± 10 y/o) underwent NIST evaluation prior to coronary angiography, of whom 81 % were positive for ischemia. There was no difference in the prevalence of positive NIST between patients with abnormal compared with normal microvascular function tested invasively (81 % vs 82 %, p = 0.94). The prevalence of CMD was similar between patients with positive versus negative NIST (51 % vs 50 %, p = 0.94). Among 114 patients with positive NIST, 56 (49.2 %) had normal microvascular function, regardless of the type of stress test used (p = 0.94), the suspected territory of ischemia (p = 0.15), or the estimated severity of the ischemia (p = 0.63).

CONCLUSION

Non-invasive stress testing may have a limited predictive value in the diagnosis of CMD in ANOCA patients. Larger prospective studies are required for better understanding of the role these tests in the diagnosis and definition of CMD.

Diagnostic performance of multi-branch coronary angiography-based index of microcirculatory resistance: a novel approach

Background

Wire-based index of microcirculatory resistance (IMR) utilizing pressure wires and thermodilution techniques for the assessment of coronary microcirculatory function, presents challenges for clinical routine use due to its complexity, time-consuming, and costly. This study introduces a novel multi-branch and wire-free method for IMR calculation based on coronary angiography. The diagnostic performance of CAG-IMR is validated within a retrospective single-center investigation.

Methods

In a retrospective single-center study, 139 patients with 201 vessels were evaluated using CAG-IMR for coronary microvascular dysfunction (CMD) detection, utilizing wire-based IMR as the reference standard. CMD was determined based on wire-based IMR ≥25U. CAG-IMR was independently calculated from diagnostic coronary angiography in a blinded fashion, employing the same diagnostic threshold of 25U for CMD identification.

Results

CAG-IMR demonstrated significant correlation (r = 0.84, p < 0.001) and good diagnostic performance AUC = 0.97 (95% CI: 0.95-0.99) compared to wire-based IMR. It exhibited the overall diagnostic accuracy at 95.0% (95% CI: 92.0%-98.0%), alongside high sensitivity (92.7%) and specificity (95.6%). The positive predictive value (PPV) stood at 84.4%, and the negative predictive value (NPV) reached 98.1%.

Conclusions

This study introduces CAG-IMR, a novel, multi-branch and wire-free method for IMR calculation. The indicator demonstrates good diagnostic accuracy and correlation with wire-based IMR in a cohort of 139 patients and 201 vessels, with the potential to enhance clinical CMD assessment.

The role of coronary microcirculation in heart failure with preserved ejection fraction: An unceasing odyssey

Heart failure with preserved ejection fraction (HFpEF) represents an entity with complex pathophysiologic pathways, among which coronary microvascular dysfunction (CMD) is believed to be an important orchestrator. Research in the field of CMD has highlighted impaired vasoreactivity, capillary rarefaction, and inflammation as potential mediators of its development. CMD can be diagnosed via several noninvasive methods including transthoracic echocardiography, cardiac magnetic resonance, and positron emission tomography. Moreover, invasive methods such as coronary flow reserve and index of microcirculatory resistance are commonly employed in the assessment of CMD. As far as the association between CMD and HFpEF is concerned, numerous studies have highlighted the coexistence of CMD in the majority of HFpEF patients. Additionally, patients affected by both conditions may be facing an adverse prognosis. Finally, there is limited evidence suggesting a beneficial effect of renin-angiotensin-aldosterone system blockers, ranolazine, and sodium-glucose cotransporter-2 inhibitors in CMD, with further evidence being awaited regarding the impact of other pharmacotherapies such as anti-inflammatory agents.

Discordant diagnosis of coronary microvascular dysfunction by microvascular resistance reserve: Transthoracic Doppler echocardiography vs bolus thermodilution method

OBJECTIVE

Epicardial stenosis and coronary microvascular dysfunction (CMD) may coexist in patients with chronic coronary syndrome (CCS). Microvascular resistance reserve (MRR) has been demonstrated to be a valid cross-modality metric using continuous saline infusion thermodilution and intracoronary Doppler flow velocity methods. This study aimed to investigate the prevalence and diagnostic concordance of CMD defined by MRR using two methods-stress transthoracic Doppler echocardiography (S-TDE) and the invasive bolus thermodilution method (B-Thermo)-in patients with functionally significant epicardial stenosis.

METHODS

We retrospectively investigated 204 left anterior descending artery (LAD) territories in CCS. All patients underwent physiological assessment using a pressure-temperature wire and S-TDE before elective fractional flow reserve (FFR)-guided percutaneous coronary intervention. The concordance rate was evaluated using κ values.

RESULTS

In the final analysis, the median age was 72 years, and 72.5% of patients were male. The median FFR value was 0.69. MRRS-TDE and MRRB-Thermo were similar (3.41 vs 3.48, P = 0.877), whereas only a weak, albeit significant relationship was observed between these two metrics (r = 0.167, P = 0.017). CMD was diagnosed in 20.6% and 32.8% of patients using S-TDE and B-Thermo, respectively, when a cutoff MRR value of 2.7 was applied. The concordance rate of CMD diagnosis between the two methods was low (κ = 0.079).

CONCLUSION

MRRS-TDE and MRRB-Thermo showed a very weak correlation in the LAD territory with functionally significant stenosis in patients with CCS. The prevalence of CMD diagnosed using MRRS-TDE and MRRB-Thermo was not comparable, and the diagnostic concordance of CMD using these two methods was very low.

Coronary microvascular dysfunction beyond the spectrum of chronic coronary syndromes

The prevalence of coronary microvascular dysfunction (CMD) beyond the spectrum of chronic coronary syndromes (CCS) is non-negligible, pertaining to pathophysiological and therapeutical implications. Thanks to the availability of accurate and safe non-invasive technique, CMD can be identified as a key player in heart failure, cardiomyopathies, Takotsubo syndrome, aortic stenosis. While CMD is widely recognized as a cause of myocardial ischemia leading to a worse prognosis even in the absence of obstructive coronary artery disease, the characterization of CMD patterns beyond CCS might provide valuable insights on the underlying disease progression, being potentially a "red flag" of adverse cardiac remodeling and a major determinant of response to therapy and outcomes. In this review, we aimed to provide an overview of the latest evidence on the prevalence, mechanistic and prognostic implications of CMD beyond the spectrum of CCS (i.e. heart failure, cardiomyopathies, Takotsubo syndrome, aortic stenosis).

Absolute coronary flow and microvascular resistance before and after transcatheter aortic valve implantation

BACKGROUND

Severe aortic stenosis (AS) is associated with left ventricular (LV) remodelling, likely causing alterations in coronary blood flow and microvascular resistance.

AIMS

We aimed to evaluate changes in absolute coronary flow and microvascular resistance in patients with AS undergoing transcatheter aortic valve implantation (TAVI).

METHODS

Consecutive patients with AS undergoing TAVI with non-obstructive coronary artery disease in the left anterior descending artery (LAD) were included. Absolute coronary flow (Q) and microvascular resistance (Rμ) were measured in the LAD using continuous intracoronary thermodilution at rest and during hyperaemia before and after TAVI, and at 6-month follow-up. Total myocardial mass and LAD-specific mass were quantified by echocardiography and cardiac computed tomography. Regional myocardial perfusion (QN) was calculated by dividing absolute flow by the subtended myocardial mass.

RESULTS

In 51 patients, Q and R were measured at rest and during hyperaemia before and after TAVI; in 20 (39%) patients, measurements were also obtained 6 months after TAVI. No changes occurred in resting and hyperaemic flow and resistance before and after TAVI nor after 6 months. However, at 6-month follow-up, a notable reverse LV remodelling resulted in a significant increase in hyperaemic perfusion (QN,hyper: 0.86 [interquartile range {IQR} 0.691.06] vs 1.20 [IQR 0.99-1.32] mL/min/g; p=0.008; pre-TAVI and follow-up, respectively) but not in resting perfusion (QN,rest: 0.34 [IQR 0.30-0.48] vs 0.47 [IQR 0.36-0.67] mL/min/g; p=0.06).

CONCLUSIONS

Immediately after TAVI, no changes occurred in absolute coronary flow or coronary flow reserve. Over time, the remodelling of the left ventricle is associated with increased hyperaemic perfusion.

Simplification of continuous intracoronary thermodilution

BACKGROUND

Continuous intracoronary thermodilution with saline allows for the accurate measurement of volumetric blood flow (Q) and absolute microvascular resistance (Rμ). However, this requires repositioning of the temperature sensor by the operator to measure the entry temperature of the saline infusate, denoted as Ti.

AIMS

We evaluated whether Ti could be predicted based on known parameters without compromising the accuracy of calculated Q. This would significantly simplify the technique and render it completely operator independent.

METHODS

In a derivation cohort of 371 patients with Q measured both at rest and during hyperaemia, multivariate linear regression was used to derive an equation for the prediction of Ti. Agreement between standard Q (calculated with measured Ti) and simplified Q (calculated with predicted Ti) was assessed in a validation cohort of 120 patients that underwent repeat Q measurements. The accuracy of simplified Q was assessed in a second validation cohort of 23 patients with [15O]H2O positron emission tomography (PET)-derived Q measurements.

RESULTS

Simplified Q exhibited strong agreement with standard Q (r=0.94, confidence interval [CI]: 0.93-0.95; intraclass correlation coefficient [ICC] 0.94, CI: 0.92-0.95; both p<0.001). Simplified Q exhibited excellent agreement with PET-derived Q (r=0.86, CI: 0.75-0.92; ICC=0.84, CI: 0.72-0.91; both p<0.001). Compared with standard Q, there were no statistically significant differences between correlation coefficients (p=0.29) or standard deviations of absolute differences with PET-derived Q (p=0.85).

CONCLUSIONS

Predicting Ti resulted in an excellent agreement with measured Ti for the assessment of coronary blood flow. It significantly simplifies continuous intracoronary thermodilution and renders absolute coronary flow measurements completely operator independent.

Development and validation of a novel angiography-derived index of absolute coronary blood flow and resistance

Intracoronary continuous thermodilution has been recently proposed as an invasive method to quantify absolute coronary flow (Qabs) and resistance (Rabs) in vivo. The aim of the present study is to develop and validate of a novel pressure-wire- and microcatheter-free surrogate of coronary flow and resistance derived from a standard coronary angiogram. Angiography derived coronary flow (Qangio) and resistance (Rangio) was prospectively validated in a two-center cohort of patients from Oxford Heart Centre and the Essex Cardiothoracic Centre. Qabs and Rabs were measured during resting and hyperemic conditions with continuous thermodilution using the Rayflow microcatheter. Qangio and Rangio were computed from the diagnostic coronary angiogram in a blinded fashion in resting and hyperemic conditions. A total of 62 patients and 115 vessels were included in the present analysis. The median Qabs at rest was 75 ml/min (53-95) and 151 ml/min (105-203) during hyperemia; Qangio at rest was 84 ml/min (66-108) and 154 ml/min (115-195) during hyperemia. There was a strong correlation between Qabs and Qangio (R = 0,72; p < 0.001, R = 0,86; p < 0.001 respectively) with satisfactory interclass correlation (0.841, 95% CI 0.509-0.957; p = 0.0003). The median Rabs was 1111 mmHg/(L/min) (830-1581.4) at rest and 454 mmHg/(L/min) (348-610) during hyperemia; angiographic resistance (Rangio) was 937.4 mmHg/(L/min) (695.4-1261.9) at rest and 492.4 mmHg/(L/min) (406-697) during hyperemia. There was a strong correlation between Rabs and Rangio in both conditions (R = 0,81; p < 0.001 and R = 0,78; p < 0.001 respectively). The was a good correlation between absolute coronary flow reserve (CFR) and angiography-derived CFR (R = 0,61; p < 0.001) and between absolute microvascular resistance reserve (MRR) and angiography-derived MRR (R = 0,49; p < 0.001).

Ischemia with non-obstructive coronary artery (INOCA): Non-invasive versus invasive techniques for diagnosis and the role of #FullPhysiology

Ischemia with non-obstructive coronary arteries (INOCA) is an increasingly recognized entity. It encompasses different pathophysiological subtypes (i.e., endotypes), including coronary microvascular dysfunction (CMD), vasospastic angina (VSA) and mixed entities resulting from the variable combination of both. Diagnosing INOCA and precisely characterizing the endotype allows for accurate medical treatment and has proven prognostic implications. A breadth of diagnostic technique is available, ranging from non-invasive approaches to invasive coronary angiography adjuvated by functional assessment and provocative tests. This review summarizes the strength and limitations of these methodologies and provides the rationale for the routine referral for invasive angiography and functional assessment in this subset of patients.

The Influence of Epicardial Resistance on Microvascular Resistance Reserve

BACKGROUND

The optimal index of microvascular function should be specific for the microvascular compartment. Yet, coronary flow reserve (CFR), despite being widely used to diagnose coronary microvascular dysfunction (CMD), is influenced by both epicardial and microvascular resistance. Conversely, microvascular resistance reserve (MRR) adjusts for fractional flow reserve (FFR), and thus is theoretically independent of epicardial resistance.

OBJECTIVES

The authors tested the hypothesis that MRR, unlike CFR, is not influenced by increasing epicardial resistance, and thus is a more specific index of microvascular function.

METHODS

In a cohort of 16 patients who had undergone proximal left anterior descending artery stenting, we created 4 grades of artificial stenosis (no stenosis, mild, moderate, and severe) using a coronary angioplasty balloon inflated to different degrees within the stent. For each stenosis grade, we calculated CFR and MRR using continuous thermodilution (64 measurements of each) to assess their response to changing epicardial resistance.

RESULTS

Graded balloon inflation resulted in a significant sequential decrease in mean FFR (no stenosis: 0.82 ± 0.05; mild: 0.72 ± 0.04; moderate: 0.61 ± 0.05; severe: 0.48 ± 0.09; P < 0.001). This translated into a linear decrease in mean hyperemic coronary flow (no stenosis: 170.5 ± 66.8 mL/min; mild: 149.8 ± 58.8 mL/min; moderate: 124.4 ± 53.0 mL/min; severe: 94.0 ± 45.2 mL/min; P < 0.001). CFR exhibited a marked linear decrease with increasing stenosis (no stenosis: 2.5 ± 0.9; mild: 2.2 ± 0.8; moderate: 1.8 ± 0.7; severe: 1.4 ± 0.6), corresponding to a decrease of 0.3 for a decrease in FFR of 0.1 (P < 0.001). In contrast, MRR exhibited a negligible decrease across all stenosis grades (no stenosis: 3.0 ± 1.0; mild: 3.0 ± 1.0; moderate: 2.9 ± 1.0; severe: 2.8 ± 1.0), corresponding to a decrease of just 0.05 for a decrease in FFR of 0.1 (P < 0.001).

CONCLUSIONS

MRR, unlike CFR, is minimally influenced by epicardial resistance, and thus should be considered the more specific index of microvascular function. This suggests that MRR can also reliably evaluate microvascular function in patients with significant epicardial disease.

Inflammation and coronary microvascular disease: relationship, mechanism and treatment

Coronary microvascular disease (CMVD) is common in patients with cardiovascular risk factors and is linked to an elevated risk of adverse cardiovascular events. Although modern medicine has made significant strides in researching CMVD, we still lack a comprehensive understanding of its pathophysiological mechanisms due to its complex and somewhat cryptic etiology. This greatly impedes the clinical diagnosis and treatment of CMVD. The primary pathological mechanisms of CMVD are structural abnormalities and/or dysfunction of coronary microvascular endothelial cells. The development of CMVD may also involve a variety of inflammatory factors through the endothelial cell injury pathway. This paper first reviews the correlation between the inflammatory response and CMVD, then summarizes the possible mechanisms of inflammatory response in CMVD, and finally categorizes the drugs used to treat CMVD based on their effect on the inflammatory response. We hope that this paper draws attention to CMVD and provides novel ideas for potential therapeutic strategies based on the inflammatory response.

Spontaneous Coronary Artery Dissection in Clinical Practice: Pathophysiology and Therapeutic Approaches

Spontaneous coronary artery dissection (SCAD) is a cause of myocardial infarction without obstructive coronary artery disease (MINOCA). It is determined by a coronary artery wall layers separation, which occurs regardless of traumatic or iatrogenic injuries. Even if it is often a missed diagnosis, its incidence is growing along with the improvement of intracoronary imaging techniques that allow for better detection. The main angiographical classification distinguishes three different forms, with slightly different prognoses at long-term follow up. SCAD is a recurrent condition, severely hampering the life quality of affected patients. The predominantly young age of patients with SCAD and the high prevalence of females among them have made the topic increasingly important, especially regarding therapeutic strategies. According to the data, the most recommended treatment is conservative, based on the use of antiplatelet agents and supportive anti-ischemic therapy. However, there are conflicting opinions concerning the need for dual antiplatelet therapy and its duration. In the case of invasive treatment, the choice between percutaneous coronary intervention and coronary artery bypass graft depends on the patient's clinical stability and the interested vessel. The purpose of the current review is to revise the pathophysiological mechanisms underlying SCAD and the current knowledge of its treatment.