Increased hyperaemic coronary microvascular resistance adds to the presence of myocardial ischaemia

Intracoronary electrocardiogram detects coronary microvascular dysfunction and ischemia in patients with no obstructive coronary arteries disease

BACKGROUND

Coronary microvascular dysfunction (CMD) is the leading cause of ischemia with no obstructive coronary arteries disease (INOCA) disease. Diagnosis of CMD relies on surrogate physiological indices without objective proof of ischemia.

OBJECTIVES

Intracoronary electrocardiogram (icECG) derived hyperemic indices may accurately and objectively detect CMD and reversible ischemia in related territory.

METHODS

INOCA patients with proven ischemia by myocardial perfusion scan (MPS) and completely normal coronary arteries underwent simultaneous intracoronary electrophysiological (icECG) and physiological (intracoronary Doppler) assessment in all 3 coronary arteries during rest and under adenosine induced hyperemia.

RESULTS

Sixty vessels in 21 patients were included in the final analysis. All patients had at least one vessel with abnormal CFR. 41 vessels had CMD (CFR < 2.5), of which 26 had increased microvascular resistance (structural CMD, HMR > 1.9 mmHg.cm-1.s) and 15 vessels had CMD (CFR < 2.5) with normal microvascular resistance (functional CMD, HMR <= 1.9 mmHg.cm-1.s). Only one-third of the patients (n = 7) had impaired CFR < 2.5 in all 3 epicardial arteries. Absolute ST shift between hyperemia and rest (∆ST) has shown the best diagnostic performance for ischemia (cut-off 0.10 mV, sensitivity: 95%, specificity: 72%, accuracy: 80%, AUC: 0.860) outperforming physiological indices (CFR: 0.623 and HMR: 0.653 DeLong's test P = .0002).

CONCLUSIONS

In INOCA patients, CMD involves coronary artery territories heterogeneously. icECG can accurately detect CMD causing perfusion abnormalities in patients with INOCA outperforming physiological CMD markers, by demonstrating actual ischemia instead of predicting the likelihood of inducible ischemia based on violated surrogate thresholds of blunted flow reserve or increased minimum microvascular resistance.

CONDENSED ABSTRACT

In 21 INOCA patients with coronary microvascular dysfunction (CMD) and myocardial perfusion scan proved ischemia, hyperemic indices of intracoronary electrocardiogram (icECG) have accurately detected vessel-specific CMD and resulting perfusion abnormalities & ischemia, outperforming invasive hemodynamic indices. Absolute ST shift between hyperemia and rest (∆ST) has shown the best classification performance for ischemia in no Obstructive Coronary Arteries (AUC: 0.860) outperforming Doppler derived CMD indices (CFR: 0.623 and HMR: 0.653 DeLong's test P = .0002).icECG can be used to diagnose CMD causing perfusion defects by demonstrating actual reversible ischemia at vessel-level during the initial CAG session, obviating the need for further costly ischemia tests.

CLINICALTRIALS

GOV: NCT05471739.

Invasive Assessment of Coronary Microcirculation: A State-of-the-Art Review

A significant proportion of patients presenting with signs and symptoms of myocardial ischemia have no "significant" epicardial disease; thereby, the assessment of coronary microcirculation gained an important role in improving diagnosis and guiding therapy. In fact, coronary microvascular dysfunction (CMD) could be found in a large proportion of these patients, supporting both symptoms and signs of myocardial ischemia. However, CMD represents a diagnostic challenge for two main reasons: (1) the small dimension of the coronary microvasculature prevents direct angiographic visualization, and (2) despite the availability of specific diagnostic tools, they remain invasive and underused in the current clinical practice. For these reasons, CMD remains underdiagnosed, and most of the patients remain with no specific treatment and quality-of-life-limiting symptoms. Of note, recent evidence suggests that a "full physiology" approach for the assessment of the whole coronary vasculature may offer a significant benefit in terms of symptom improvement among patients presenting with ischemia and non-obstructive coronary artery disease. We analyze the pathophysiology of coronary microvascular dysfunction, providing the readers with a guide for the invasive assessment of coronary microcirculation, together with the available evidence supporting its use in clinical practice.

Particularities of coronary physiology in patients with atrial fibrillation: insights from combined pressure and flow indices measurements

Background

Symptoms suggestive of myocardial ischemia are frequently encountered in patients with atrial fibrillation (AF) even in the absence of obstructive coronary artery disease. Nevertheless, an in-depth characterisation of coronary physiology in patients with AF is currently lacking.

Objectives

We aim to provide an insight into the characteristics of coronary physiology in AF, by performing simultaneous invasive measurements of coronary flow- and pressure- indices in a real-life population of patients with AF and indication of coronary angiography.

Methods

This is a prospective open label study including patients with permanent or persistent AF and indication of coronary angiography showing intermediate coronary stenosis requiring routine physiological assessment (n = 18 vessels from 14 patients). We measured FFR (fractional flow reserve), and Doppler-derived coronary flow indices, including CFR (coronary flow reserve) and HMR (hyperaemic microvascular resistance).

Results

From the analysed vessels, 18/18 vessels (100%) presented a pathological CFR (<2.5), indicative of coronary microvascular dysfunction (CMD), and 3/18 (17%) demonstrated obstructive epicardial coronary disease (FFR ≤ 0.8). A large proportion of vessels (15/18; 83%) showed discordant FFR/CFR with preserved FFR and low CFR. 47% of the coronary arteries in patients with AF and non-obstructive epicardial coronary disease presented structural CMD (HMR ≥ 2.5 mmHg/cm/s), and were associated with high BMR and an impaired response to adenosine. Conversely, vessels from patients with AF and non-obstructive epicardial coronary disease with functional CMD (HMR < 2.5 mmHg/cm/s) showed higher bAPV. The permanent AF subpopulation presented increased values of HMR and BMR compared to persistent AF, while structural CMD was more often associated with persistent symptoms at 3 months, taking into account the limited sample size of our study.

Conclusion

Our findings highlight a systematically impaired CFR in patients with AF even in the absence of obstructive epicardial coronary disease, indicative of CMD. In addition, patients with AF presented more prevalent structural CMD (HMR ≥ 2.5 mmHg/cm/s), characterized by reduced hyperaemic responses to adenosine, possibly interfering with the FFR assessment.

Sex differences in coronary microvascular resistance measured by a computational fluid dynamics model

Background

Increased coronary microvascular resistance (CMVR) is associated with coronary microvascular dysfunction (CMD). Although CMD is more common in women, sex-specific differences in CMVR have not been demonstrated previously.

Aim

To compare CMVR between men and women being investigated for chest pain.

Methods and results

We used a computational fluid dynamics (CFD) model of human coronary physiology to calculate absolute CMVR based on invasive coronary angiographic images and pressures in 203 coronary arteries from 144 individual patients. CMVR was significantly higher in women than men (860 [650-1,205] vs. 680 [520-865] WU, Z = -2.24, p = 0.025). None of the other major subgroup comparisons yielded any differences in CMVR.

Conclusion

CMVR was significantly higher in women compared with men. These sex-specific differences may help to explain the increased prevalence of CMD in women.

The Association of Obstructive Sleep Apnea in Ischemia with No Obstructive Coronary Artery Disease - A Pilot Study

Obstructive sleep apnea (OSA) is increasingly recognized to be a risk factor for cardiovascular disease. This pilot study assessed the association of OSA and invasive coronary microvascular function in patients with ischemia with no obstructive coronary artery disease (INOCA). Forty-two patients with angina, were prospectively screened at a single tertiary centre covering the northern metropolitan area of South Australia, from February 2018 to December 2020 (ACTRN12618000149268). Forty patients were invited into to this observational study after coronary angiography demonstrated INOCA and functional coronary vasomotor disorder (n = 40). Twenty one participants subsequently underwent a sleep study for OSA diagnosis while 9 participants had prior formal diagnosis of OSA (ACTRN12618000227291). Of the 30 participants with OSA data, 87% (n = 26) had a diagnosis of OSA. Accordingly, 11 with mild severity, 7 with moderate severity and 8 with severe OSA. No OSA was observed in 4 participants. Participants with OSA were older [61.4±8.7 vs 49.9±9.7, P = 0.002] with similar clinical characteristics for the pattern and severity of angina and other co-morbidities. 73.3% (n = 22) had abnormal functional disorders of the epicardial coronary arteries and/or coronary microcirculation. On multivariate analysis, OSA was the only statistically significant association with functional coronary microvascular disorders [OR 53.95, 1.41 -2065.01, P = 0.032]. This study provided an observation of a significant correlation between INOCA with abnormal coronary vasomotor function and OSA in an Australian cohort. This correlation supports a possible pathophysiological interplay between these two conditions that needs to be further evaluated. The benefit of treatment of OSA in this subset remains unknown.

Reference values for intracoronary Doppler flow velocity-derived hyperaemic microvascular resistance index

BACKGROUND

Invasive assessments of microvascular function are rapidly becoming an integral part of physiological assessment in chronic coronary syndromes.

OBJECTIVE

We aimed to establish a reference range for Doppler flow velocity-derived hyperaemic microvascular resistance index (HMR) in a cohort of angina with no significant epicardial coronary obstruction (ANOCA) patients with no structural pathophysiological alterations in the coronary circulation.

METHODS

The reference population consisted of ANOCA patients undergoing invasive coronary vasomotor function assessment who had a coronary flow reserve (CFR) >2.5, and had either (1) tested negatively for spasm provocation (n = 12) or (2) tested positively with only angina at rest (n = 29). A reference range for HMR was established using a non-parametric method and correlations with clinical characteristics were determined using a spearman rank correlation analysis.

RESULTS

In 41 patients median HMR amounted to 1.6 mmHg/cm/s [Q1, Q3: 1.3, 2.2 mmHg/cm/s]. The reference range for HMR that is applicable to 95% of the population was 0.8 mmHg/cm/s (90% CI: 0.8-1.0 mmHg/cm/s) to 2.7 mmHg/cm/s (90% CI: 2.6-2.7 mmHg/cm/s). No significant correlations were found between HMR and clinical characteristics.

CONCLUSION

In this reference population undergoing invasive coronary vasomotor function testing, the 90% confidence interval of the HMR upper limit of normal ranges from 2.6 to 2.7 mmHg/cm/s. A > 2.5 mmHg/cm/s HMR threshold can be used to identify abnormal microvascular resistance in daily clinical practice.

Invasive evaluation of coronary microvascular dysfunction

Coronary microvascular dysfunction (CMD) is a prevalent cause of ischemic heart disease and is associated with poorer quality of life and worse patient outcomes. Both functional and structural abnormalities of the microcirculation can generate ischemia in the absence of epicardial stenosis or worsen concomitant obstructive coronary artery disease (CAD). The invasive assessment of CMD allows for the evaluation of the entirety of the coronary vascular tree, from the large epicardial vessels to the microcirculation, and enables the study of vasomotor function through vasoreactivity testing. The standard evaluation of CMD includes vasomotor assessment with acetylcholine, as well as flow- and resistance-derived indices calculated with either thermodilution or Doppler guidewires. Tailored treatment based upon the information gathered from the invasive evaluation of CMD has been demonstrated to reduce the burden of angina; therefore, a thorough understanding of these procedures is warranted with the aim of improving the quality of life of the patient. This review summarizes the most widespread approaches for the invasive evaluation of CMD, with a focus on patients with ischemia and non-obstructive CAD.

Prognostic value of microvascular resistance and its association to fractional flow reserve: a DEFINE-FLOW substudy

Objective

This study aimed to evaluate the prognostic value of hyperemic microvascular resistance (HMR) and its relationship with hyperemic stenosis resistance (HSR) index and fractional flow reserve (FFR) in stable coronary artery disease.

Methods

This is a substudy of the DEFINE-FLOW cohort (NCT02328820), which evaluated the prognosis of lesions (n=456) after combined FFR and coronary flow reserve (CFR) assessment in a prospective, non-blinded, non-randomised, multicentre study in 12 centres in Europe and Japan. Participants (n=430) were evaluated by wire-based measurement of coronary pressure, flow and vascular resistance (ComboWire XT, Phillips Volcano, San Diego, California, USA).

Results

Mean FFR and CFR were 0.82±0.10 and 2.2±0.6, respectively. When divided according to FFR and CFR thresholds (above and below 0.80 and 2.0, respectively), HMR was highest in lesions with FFR>0.80 and CFR<2.0 (n=99) compared with lesions with FFR≤0.80 and CFR≥2.0 (n=68) (2.92±1.2 vs 1.91±0.64 mm Hg/cm/s, p<0.001). The FFR value was proportional to the ratio between HMR and the HMR+HSR (total resistance), 95% limits of agreement (−0.032; 0.019), bias (−0.003±0.02) and correlation (r²=0.98, p<0.0001). Cox regression model using HMR as continuous parameter for target vessel failure showed an HR of 1.51, 95% CI (0.9 to 2.4), p=0.10.

Conclusions

Increased HMR was not associated with a higher rate of adverse clinical events, in this population of mainly stable patients. FFR can be equally well expressed as HMR/HMR+HSR, thereby providing an alternative conceptual formulation linking epicardial severity with microvascular resistance.

Trial registration number

NCT02328820.

Impact of invasive aortic pulse pressure on coronary microvascular endothelial-independent dysfunction and on mortality in non-obstructive coronary artery disease

Background

Pulse pressure (PP), a raw index of arterial stiffness, is inversely related to coronary microvascular function, even among patients with non-obstructive coronary artery disease (CAD), as per non-invasive studies. We aimed to determine whether invasive aortic PP is associated with coronary microvascular endothelial dysfunction (CMED) and/or coronary microvascular endothelial independent dysfunction (CMEID) in patients with non-obstructed CAD.

Methods

We retrospectively analysed a cohort of 1894 patients (mean age, 51.2 years; 1261 (66.6%) women) who presented with chest pain and non-obstructive CAD (angiographic stenosis <50%); coronary vasoreactivity was assessed in the mid-left anterior descending artery. The patients were classified based on whether aortic PP was high (≥50 mm Hg). CMEID was defined as abnormal coronary flow reserve (<2.5) or hyperaemic myocardial resistance (>2.0 mm Hg/cm/s), CMED was defined as abnormal acetylcholine-induced per cent change of coronary blood flow (≤50%).

Results

Patients with high aortic PP had a higher rate of CMEID than those with low aortic PP (40.9 vs 25.2%, p<0.001). Conversely, aortic PP was not associated with CMED. On multivariate analysis, high aortic PP was associated with CMEID occurrence (OR 1.42, 95% CI 1.13 to 1.78; p=0.003). On follow-up (median, 150 months), all-cause death was more frequent among patients with vs without high aortic PP (20.1% vs 7.3%, log-rank p<0.001) and HR was 2.08 (95% CI 1.34 to 3.32, p=0.002) on multivariate cox regression analysis. Furthermore, among patients with low aortic PP, CMEID was an independent risk factor for all-cause mortality (HR 2.04, 95% CI 1.01 to 4.16, p=0.048).

Conclusion

In patients with non-obstructive CAD, invasive aortic PP was significantly associated with CMEID, but not with CMED. High aortic PP was an independent predictor of all-cause mortality, but CMEID was an independent risk factor in patients with low aortic PP.

Invasive Assessment of Coronary Microvascular Function

The critical role of the coronary microvascular compartment and its invasive functional assessment has become apparent in light of the significant proportion of patients presenting signs and symptoms of myocardial ischemia, despite the absence of epicardial disease, or after the adequate treatment of it. However, coronary microvascular dysfunction (CMD) represents a diagnostic challenge because of the small dimensions of the coronary microvasculature, which prevents direct angiographic visualization. Several diagnostic tools are now available for the invasive assessment of the coronary microvascular function, which, in association with the physiological indices used to investigate the epicardial department, may provide a comprehensive evaluation of the coronary circulation as a whole. Recent evidence suggests that the physiology-guided management of CMD, although apparently costly and time-consuming, may offer a net clinical benefit in terms of symptom improvement among patients with angina and ischemic heart disease. However, despite the results of several observational studies, the prognostic effect of the physiology-driven management of CMD within this population is currently a matter of debate, and therefore represents an unmet clinical need that urgently deserves further investigation.

Vasomotor Dysfunction in Patients with Ischemia and Non-Obstructive Coronary Artery Disease: Current Diagnostic and Therapeutic Strategies

Many patients who present with symptoms or objective evidence of ischemia have no or non-physiologically-significant disease on invasive coronary angiography. The diagnosis of ischemic heart disease is thus often dismissed, and patients receive false reassurance or other diagnoses are pursued. We now know that a significant proportion of these patients have coronary microvascular dysfunction and/or vasospastic disease as the underlying pathophysiology of their clinical presentation. Making the correct diagnosis of such abnormalities is important not only because they impact the quality of life, with recurring symptoms and unnecessary repeated testing, but also because they increase the risk for adverse cardiovascular events. The mainstay of diagnosis remains an invasive comprehensive physiologic assessment, which further allows stratifying these patients into appropriate “endotypes”. It has been shown that tailoring treatment to the patient’s assigned endotype improves symptoms and quality of life. In addition to the conventional drugs used in chronic stable angina, multiple newer agents are being investigated. Moreover, innovative non-pharmacologic and interventional therapies are emerging to provide a bail-out in refractory cases. Many of these novel therapies fail to show consistent benefits, but others show quite promising results.

Contribution of Age-Related Microvascular Dysfunction to Abnormal Coronary: Hemodynamics in Patients With Ischemic Heart Disease

OBJECTIVES

This study sought to investigate the contribution of age-related microcirculatory dysfunction to abnormal coronary hemodynamics in patients with coronary atherosclerosis.

BACKGROUND

Impairment in myocardial blood supply in patients with coronary atherosclerosis can be accentuated due to age-related changes in microcirculatory function.

METHODS

Intracoronary pressure and flow were measured with the Doppler technique in 299 vessels (228 patients), and the thermodilution technique in 120 vessels (99 patients). In 172 patients, Doppler measurements were also performed in unobstructed vessels. Associations of coronary hemodynamics with aging were studied in both the stenosed and unobstructed arteries.

RESULTS

Aging was associated with a progressive increase in minimal microvascular resistance and a progressive decrease in hyperemic flow in both obstructed and nonobstructed coronary arteries. As such, coronary flow reserve decreased with advancing age. Epicardial stenosis severity assessed by resting Pd/Pa, basal stenosis resistance index, and hyperemic stenosis resistance index was equivalent across age groups. By contrast, fractional flow reserve increased with advancing age. Consequently, the adjusted risk of a fractional flow reserve/coronary flow reserve pattern reflective of concomitant focal epicardial and diffuse or microvascular disease (relative risk: 1.6; 95% confidence interval: 1.1 to 2.3; p = 0.017) increased with advancing age, whilst the adjusted risk of a fractional flow reserve/coronary flow reserve pattern reflective of non-flow-limiting stenosis with a healthy microcirculation decreased (relative risk: 0.7; 95% CI: 0.5 to 1.0; p = 0.022).

CONCLUSIONS

Aging is associated with progressive pan-myocardial impairment of coronary vasodilatory capacity due to an increase in minimal microvascular resistance. Concomitant aging-related impairment in microvascular function impacts the pathophysiology of ischemic heart disease in the individual patient and is not adequately identified by hyperemic coronary pressure measurements alone.

Clinical and coronary haemodynamic determinants of recurrent chest pain in patients without obstructive coronary artery disease - A pilot study

BACKGROUND

Coronary haemodynamic testing frequently identifies abnormal pathophysiological parameters in patients with angina and non-obstructed coronaries on angiography (NoCAD) but the clinical utility of these measures has received limited attention.

OBJECTIVE

This study aims to identify the clinical and coronary haemodynamic determinants of recurrent chest pain at one month in patients with NoCAD.

METHODS

Patients with angina, NoCAD (<50% stenosis) and normal LV systolic function underwent invasive coronary haemodynamic testing involving: (1) angiographic TIMI frame and opacification rate, (2) microvascular functional measures including coronary flow reserve (CFR) and hyperaemic microvascular resistance (HMR), (3) coronary endothelial function assessment with low dose intracoronary acetylcholine (IC-ACh) infusions (0.18 μg/min & 1.8 μg/min over 2 min), and (4) Provocative spasm testing with high dose IC-ACh boluses (25, 50 and 100 μg). Clinical and health status were assessed at baseline and one month.

RESULTS

In the 49 NoCAD patients (78% female, mean age of 54 ± 11) undergoing comprehensive coronary haemodynamic testing, 33 (67%) continued to experience chest pain at one month. Determinants of recurrent chest pain on univariate analysis included baseline chest pain status or a HMR > 1.9. Multivariate logistic regression analysis identified frequent angina at baseline (OR: 68.9 [4.1, 1165.0], p = 0.003), previous unstable angina admission (OR: 43.9 [3.5, 547.9], p = 0.003) and a HMR > 1.9 (OR: 15.6 [2.1, 114.0], p = 0.007) as independent predictors of recurrent chest pain.

CONCLUSION

In this small pilot study, an abnormal HMR was the only coronary haemodynamic parameter that was a determinant of ongoing angina at short-term follow-up.

Pathophysiological Significance of Velocity-Based Microvascular Resistance at Maximal Hyperemia in Peripheral Artery Disease

AIM

Maximal hyperemic response, leading to examination of microvascular resistance in lower-limb lesions is not well understood. This study aimed to investigate the infrainguinal arterial physiological response through a hyperemic condition and the pathophysiological significance of microvascular resistance in peripheral artery disease.

METHODS

Sixteen limbs with focal stenosis of the superficial femoral artery (SFA) and 16 control limbs were analyzed. We assessed the fractional flow reserve (FFR), vascular flow reserve (VFR), and hyperemic microvascular resistance (h-MR) of the SFA with a pressure/Doppler flow sensor-tipped combination guidewire before and after endovascular therapy (EVT). Skin perfusion pressure (SPP) on both the dorsal and the plantar sides of the foot was measured at baseline before and after the endovascular procedures.

RESULTS

FFR (p＜0.05) and VFR (p＜0.05), but not h-MR, improved after EVT. There was no association between h-MR and FFR or VFR before EVT. h-MR was negatively correlated with the dorsal SPP before EVT (r=－0.589, p＜0.05). h-MR in patients with high h-MR before EVT significantly decreased after EVT (p＜0.05). Patients with high, but not those with low, h-MR before EVT exhibited a significant increase in dorsal and plantar SPP after EVT (p＜0.05, each).

CONCLUSION

EVT for SFA stenosis improved FFR and VFR comprehensively, with no apparent change in h-MR. However, high h-MR before EVT may play a predictive role for limb perfusion improvement associated with h-MR reduction after EVT.

Assessing Coronary Blood Flow Physiology in the Cardiac Catheterisation Laboratory

Background:

Contemporary management of coronary disease focuses on the treatment of stenoses in the major epicardial vessels. However, myocardial blood flow is known to be contingent on a range of factors in addition to the patency of the epicardial vessels. These include anatomical and physiological factors such as the extent of myocardium supplied by the vessel, systemic blood pres-sure, the natural variation in vascular tone in response to physiological needs which allows for coro-nary autoregulation and pathological factors such as the presence of downstream obstruction to flow due to disease of the small coronary vessels or myocardium. The assessment of clinical effectiveness and adequacy of coronary revascularisation requires the ability to comprehensively and accurately as-sess and measure myocardial perfusion.

Conclusion:

In this article, we review the current methods of evaluating coronary blood flow and my-ocardial perfusion in the cardiac catheterisation laboratory.

Evaluation of intermediate coronary stenoses in acute coronary syndromes using pressure guidewire

Fractional flow reserve (FFR) is increasingly used to guide myocardial revascularisation. However, supporting evidence regarding its use originates from studies that have enrolled mainly patients with stable angina, while patients with acute coronary syndromes (ACS) have not been included. Notably, multifactorial microvascular dysfunction and an increased sympathetic tone in patients with ACS may lead to blunted response to adenosine and false-negative results of FFR due to submaximal hyperaemia. This may raise the possibility of deferring treatment of stenosis that instead would have needed dilatation, thus leaving a residual risk of preventable cardiac events. In this literature review, we aim at summarising laboratory and clinical investigations concerning the use of FFR in culprit and non-culprit lesions in ACS. Furthermore, we will report recent data on instantaneous wave-free ratio, an adenosine-free index of functional stenosis severity, in stable coronary artery disease and in patients with ACS.