Arterial pulse wave dynamics after percutaneous aortic valve replacement: fall in coronary diastolic suction with increasing heart rate as a basis for angina symptoms in aortic stenosis.

BACKGROUND: Aortic stenosis causes angina despite unobstructed arteries. Measurement of conventional coronary hemodynamic parameters in patients undergoing valvular surgery has failed to explain these symptoms. With the advent of percutaneous aortic valve replacement (PAVR) and developments in coronary pulse wave analysis, it is now possible to instantaneously abolish the valvular stenosis and to measure the resulting changes in waves that direct coronary flow. METHODS AND RESULTS: Intracoronary pressure and flow velocity were measured immediately before and after PAVR in 11 patients with unobstructed coronary arteries. Using coronary pulse wave analysis, we calculated the intracoronary diastolic suction wave (the principal accelerator of coronary blood flow). To test physiological reserve to increased myocardial demand, we measured at resting heart rate and during pacing at 90 and 120 bpm. Before PAVR, the basal myocardial suction wave intensity was 1.9±0.3×10(-5) W · m(-2) · s(-2), and this increased in magnitude with increasing severity of aortic stenosis (r=0.59, P=0.05). This wave decreased markedly with increasing heart rate (ß coefficient=-0.16×10(-4) W · m(-2) · s(-2); P<0.001). After PAVR, despite a fall in basal suction wave (1.9±0.3 versus 1.1±0.1×10(-5) W · m(-2) · s(-2); P=0.02), there was an immediate improvement in coronary physiological reserve with increasing heart rate (ß coefficient=0.9×10(-3) W · m(-2) · s(-2); P=0.014). CONCLUSIONS: In aortic stenosis, the coronary physiological reserve is impaired. Instead of increasing when heart rate rises, the coronary diastolic suction wave decreases. Immediately after PAVR, physiological reserve returns to a normal positive pattern. This may explain how aortic stenosis can induce anginal symptoms and their prompt relief after PAVR. Clinical Trial Registration- URL: http://www.clinicaltrials.gov. Unique identifier: NCT01118442.

The arterial reservoir pressure increases with aging and is the major determinant of the aortic augmentation index.

The augmentation index predicts cardiovascular mortality and is usually explained as a distally reflected wave adding to the forward wave generated by systole. We propose that the capacitative properties of the aorta (the arterial reservoir) also contribute significantly to the augmentation index and have calculated the contribution of the arterial reservoir, independently of wave reflection, and assessed how these contributions change with aging. In 15 subjects (aged 53 +/- 10 yr), we measured pressure and Doppler velocity simultaneously in the proximal aorta using intra-arterial wires. We calculated the components of augmentation pressure in two ways: 1) into forward and backward (reflected) components by established separation methods, and 2) using an approach that accounts for an additional reservoir component. When the reservoir was ignored, augmentation pressure (22.7 +/- 13.9 mmHg) comprised a small forward wave (peak pressure = 6.5 +/- 9.4 mmHg) and a larger backward wave (peak pressure = 16.2 +/- 7.6 mmHg). After we took account of the reservoir, the contribution to augmentation pressure of the backward wave was reduced by 64% to 5.8 +/- 4.4 mmHg (P < 0.001), forward pressure was negligible, and reservoir pressure was the largest component (peak pressure = 19.8 +/- 9.3 mmHg). With age, reservoir pressure increased progressively (9.9 mmHg/decade, r = 0.69, P < 0.001). In conclusion, the augmentation index is principally determined by aortic reservoir function and other elastic arteries and only to a minor extent by reflected waves. Reservoir function rather than wave reflection changes markedly with aging, which accounts for the age-related changes in the aortic pressure waveform.

Management of Acute Coronary Syndromes During the Coronavirus Disease 2019 Pandemic: Deviations from Guidelines and Pragmatic Considerations for Patients and Healthcare Workers.

Coronavirus disease 2019 (COVID-19) is forcing cardiology departments to rapidly adapt existing clinical guidelines to a new reality and this is especially the case for acute coronary syndrome pathways. In this focused review, the authors discuss how COVID-19 is affecting acute cardiology care and propose pragmatic guideline modifications for the diagnosis and management of acute coronary syndrome patients, particularly around the appropriateness of invasive strategies as well as length of hospital stay. The authors also discuss the use of personal protective equipment for healthcare workers in cardiology. Based on shared global experiences and growing peer-reviewed literature, it is possible to put in place modified acute coronary syndrome treatment pathways to offer safe pragmatic decisions to patients and staff.

Evidence of a dominant backward-propagating "suction" wave responsible for diastolic coronary filling in humans, attenuated in left ventricular hypertrophy.

BACKGROUND: Coronary blood flow peaks in diastole when aortic blood pressure has fallen. Current models fail to completely explain this phenomenon. We present a new approach-using wave intensity analysis-to explain this phenomenon in normal subjects and to evaluate the effects of left ventricular hypertrophy (LVH). METHOD AND RESULTS: We measured simultaneous pressure and Doppler velocity with intracoronary wires in the left main stem, left anterior descending, and circumflex arteries of 20 subjects after a normal coronary arteriogram. Wave intensity analysis was used to identify and quantify individual pressure and velocity waves within the coronary artery circulation. A consistent pattern of 6 predominating waves was identified. Ninety-four percent of wave energy, accelerating blood forward along the coronary artery, came from 2 waves: first a pushing wave caused by left ventricular ejection-the dominant forward-traveling pushing wave; and later a suction wave caused by relief of myocardial microcirculatory compression-the dominant backward-traveling suction wave. The dominant backward-traveling suction wave (18.2+/-13.7 x 10(3) W m(-2)s(-1), 30%) was larger than the dominant forward-traveling pushing wave (14.3+/-17.6 x 10(3) W m(-2) s(-1), 22.3%, P =0.001) and was associated with a substantially larger increment in coronary blood flow velocity (0.51 versus 0.14 m/s, P <0.001). In LVH, the dominant backward-traveling suction wave percentage was significantly decreased (33.1% versus 26.9%, P =0.01) and inversely correlated with left ventricular septal wall thickness (r =-0.52, P <0.02). CONCLUSIONS: Six waves predominantly drive human coronary blood flow. Coronary flow peaks in diastole because of the dominance of a "suction" wave generated by myocardial microcirculatory decompression. This is significantly reduced in LVH.

Attenuation of reflected waves in man during retrograde propagation from femoral artery to proximal aorta.

BACKGROUND: Wave reflection may be an important influence on blood pressure, but the extent to which reflections undergo attenuation during retrograde propagation has not been studied. We quantified retrograde transmission of a reflected wave created by occlusion of the left femoral artery in man. METHODS: 20 subjects (age 31-83 years; 14 male) underwent invasive measurement of pressure and flow velocity with a sensor-tipped intra-arterial wire at multiple locations distal to the proximal aorta before, during and following occlusion of the left femoral artery by thigh cuff inflation. A numerical model of the circulation was also used to predict reflected wave transmission. Wave reflection was measured as the ratio of backward to forward wave energy (WRI) and the ratio of peak backward to forward pressure (Pb/Pf). RESULTS: Cuff inflation caused a marked reflection which was largest at 5-10 cm from the cuff (change (Δ) in WRI=0.50 (95% CI 0.38, 0.62); p<0.001, ΔPb/Pf=0.23 (0.18-0.29); p<0.001). The magnitude of the cuff-induced reflection decreased progressively at more proximal locations and was barely discernible at sites>40 cm from the cuff including in the proximal aorta. Numerical modelling gave similar predictions to those observed experimentally. CONCLUSIONS: Reflections due to femoral artery occlusion are markedly attenuated by the time they reach the proximal aorta. This is due to impedance mismatches of bifurcations traversed in the backward direction. This degree of attenuation is inconsistent with the idea of a large discrete reflected wave arising from the lower limb and propagating back into the aorta.

Resolving the paradox of randomised controlled trials and observational studies comparing multi-vessel angioplasty and culprit only angioplasty at the time of STEMI.

BACKGROUND: Patients presenting with ST-elevation myocardial infarction commonly have multi-vessel coronary artery disease. After the culprit artery is treated, the optimal treatment strategy for the residual disease is not yet defined. Large observational studies suggest that treatment of residual disease should be deferred but smaller randomised controlled trials (RCTs) suggest multi-vessel primary percutaneous coronary intervention (MV-PPCI) at the time of STEMI is safe. We examine if allocation bias of high-risk patients could explain the conflicting results between observational studies and RCTs and aim to resolve the paradox between the two. METHODS: A meta-analysis of registries comparing culprit-only PPCI to MV-PPCI was performed. We then determined if high-risk patients were more likely to be allocated to MV-PPCI. A meta-regression was performed to determine if any allocation bias of high-risk patients could explain the difference in outcomes between therapies. RESULTS: 47,717 patients (19 studies) were eligible. MV-PPCI had higher mortality than culprit-only PPCI (OR 1.59, 95% CI 1.12 to 2.24, p=0.03). However, higher risk patients were more likely to be allocated to MV-PPCI (OR 1.45, 95% CI 1.18 to 1.78, p=0.0005). When this was accounted for, there was no difference in mortality between culprit-only PPCI and MV-PPCI (OR 0.99, 95% CI 0.69 to 1.41, p=0.94). DISCUSSION: Clinicians preferentially allocate higher-risk patients to MV-PPCI at the time of STEMI, resulting in observational studies reporting higher mortality with this strategy. When this is accounted for, these large observational studies in 'real world' patients support the conclusion of the smaller RCTs in the field: MV-PPCI has equivalent mortality to a culprit-only approach.

Cannabis as a precipitant of cardiovascular emergencies.

Cannabis smoking is on the increase both in the United Kingdom and in the United States. For over three decades it has been known that cannabis has pathophysiological effects on the cardiovascular system, and previously an association with an increased risk of myocardial infarction has been reported. However, it is not yet known whether cannabis contributes directly to coronary artery disease. We describe two distinct cases; in the first cannabis use precipitated a malignant arrhythmia in a patient with critical ischaemia from longstanding coronary artery disease. In the second, a young patient presented with an acute myocardial infarction that had started whilst smoking marijuana; subsequently diffuse coronary artery disease was found at angiography despite the patient's low risk factor status. Patients who are known cannabis smokers and who have cardiovascular disease should be warned that it is likely to aggravate coronary ischaemia, and may even trigger myocardial infarction.

A new method of applying randomised control study data to the individual patient: A novel quantitative patient-centred approach to interpreting composite end points.

BACKGROUND: Modern randomised controlled trials typically use composite endpoints. This is only valid if each endpoint is equally important to patients but few trials document patient preference and seek the relative importance of components of combined endpoints. If patients weigh endpoints differentially, our interpretation of trial data needs to be refined. METHODS AND RESULTS: We derive a quantitative, structured tool to determine the relative importance of each endpoint to patients. We then apply this tool to data comparing angioplasty with drug-eluting stents to bypass surgery. The survey was administered to patients undergoing cardiac catheterisation. A meta-analysis comparing coronary artery bypass grafting (CABG) to percutaneous coronary interventuin (PCI) was then performed using (a) standard MACE and (b) patient-centred MACE. Patients considered stroke worse than death (stroke 102.3 ± 19.6%, p < 0.01), and MI and repeat revascularisation less severe than death (61.9 ± 26.8% and 41.9 ± 25.4% respectively p < 0.01 for both). 7 RCTs (5251 patients) were eligible. Meta-analysis demonstrated that standard MACE occurs more frequently with PCI than surgery (OR 1.44; 95% CI 1.10 to 1.87; p = 0.007). Re-analysis using patient-centred MACE found no significant difference between PCI and CABG (OR 1.22, 95% CI 0.97 to 1.53; p = 0.10). CONCLUSIONS: Patients do not consider the constituent endpoints of MACE equal. We derive a novel patient-centred metric that recognises and quantifies the differences attributed to each endpoint. When patient preference data are applied to contemporary trial results, there is no significant difference between PCI and CABG. Responses from individual patients in clinic could be used to give individual patients a recommendation that is truly personalised.

Change in coronary blood flow after percutaneous coronary intervention in relation to baseline lesion physiology: results of the JUSTIFY-PCI study.

BACKGROUND: Percutaneous coronary intervention (PCI) aims to increase coronary blood flow by relieving epicardial obstruction. However, no study has objectively confirmed this and assessed changes in flow over different phases of the cardiac cycle. We quantified the change in resting and hyperemic flow velocity after PCI in stenoses defined physiologically by fractional flow reserve and other parameters. METHODS AND RESULTS: Seventy-five stenoses (67 patients) underwent paired flow velocity assessment before and after PCI. Flow velocity was measured over the whole cardiac cycle and the wave-free period. Mean fractional flow reserve was 0.68±0.02. Pre-PCI, hyperemic flow velocity is diminished in stenoses classed as physiologically significant compared with those classed nonsignificant (P<0.001). In significant stenoses, flow velocity over the resting wave-free period and hyperemic flow velocity did not differ statistically. After PCI, resting flow velocity over the wave-free period increased little (5.6±1.6 cm/s) and significantly less than hyperemic flow velocity (21.2±3 cm/s; P<0.01). The greatest increase in hyperemic flow velocity was observed when treating stenoses below physiological cut points; treating stenoses with fractional flow reserve ≤0.80 gained Δ28.5±3.8 cm/s, whereas those fractional flow reserve >0.80 had a significantly smaller gain (Δ4.6±2.3 cm/s; P<0.001). The change in pressure-only physiological indices demonstrated a curvilinear relationship to the change in hyperemic flow velocity but was flat for resting flow velocity. CONCLUSIONS: Pre-PCI physiology is strongly associated with post-PCI increase in hyperemic coronary flow velocity. Hyperemic flow velocity increases 6-fold more when stenoses classed as physiologically significant undergo PCI than when nonsignificant stenoses are treated. Resting flow velocity measured over the wave-free period changes at least 4-fold less than hyperemic flow velocity after PCI.

Ethnic differences in carotid and left ventricular hypertrophy.

OBJECTIVES: Afro-Caribbean subjects have a higher prevalence of hypertension, a lower prevalence of ischaemic heart disease and a higher premature mortality compared to White Europeans. Left ventricular hypertrophy (LVH) is also more prevalent in Afro-Caribbeans even at similar levels of blood pressure. It is widely believed that carotid artery intima-media thickening (IMT) represents an early marker for the development of atheroma, and carotid IMT and LVH are associated in White populations. Whether the relationship between carotid IMT and LVH is similar in Black subjects is unknown. METHODS: Thirty-eight subjects were studied using carotid and femoral ultrasonography and echocardiography; 19 Afro-Caribbean and 19 White European subjects were matched for age, sex and mean 24 h systolic blood pressure. RESULTS: The Afro-Caribbean group had a significantly greater left ventricular mass index (LVMI) compared to the White European: 136.4 +/- 6.1 versus 112.4 +/- 6.2 g/m2, P < 0.01. However, carotid IMT, carotid diameter, femoral IMT and femoral diameter were similar between the groups: 0.75 +/- 0.02 versus 0.77 +/- 0.04 mm, 6.54 +/- 0.15 versus 6.56 +/- 0.16 mm, 0.66 +/- 0.03 versus 0.68 +/- 0.03 mm and 8.40 +/- 0.33 versus 8.25 +/- 0.23 mm, respectively. CONCLUSIONS: Afro-Caribbean subjects with similar blood pressures have similar mean carotid and femoral IMTs compared to White Europeans, in spite of marked differences in LVMI. Whether this reflects a discrepancy in the degree of cardiovascular risk for similar levels of LVMI or whether this is a reflection of an altered pattern of target organ damage associated with hypertension in Afro-Caribbean subjects is unclear.

Midwall myocardial shortening in athletic left ventricular hypertrophy.

BACKGROUND: Patients with pathological left ventricular hypertrophy have depressed midwall systolic shortening in spite of normal indices of left ventricular chamber function and a reduced midwall function has been observed to be an independent predictor of cardiovascular risk. Whether midwall shortening is depressed in physiological hypertrophy is unknown. METHODS: Forty-two subjects, 27 athletes and 15 age- and sex-matched normal control subjects (group 1) were studied. The athletes were divided into those with eccentric hypertrophy (group 2) and those with concentric hypertrophy (group 3). Systolic left ventricular function was assessed at the midwall and endocardium using two-dimensional echocardiography in all subjects. RESULTS: Left ventricular mass index was significantly greater in both athletic groups than in controls (group 1, 101+/-5.8 g/m(2), group 2, 141+/-11.1*, group 3, 155+/-5.8*; *P<0.01 compared with group 1). Left ventricular systolic function assessed at the endocardium was similar among all three groups (ejection fraction: group 1, 66.2+/-2.38, group 2, 66.8+/-1.44, group 3, 63.7+/-1.66%; endocardial fractional shortening: group 1, 37.1+/-1.71, group 2, 37.6+/-1.13, group 3, 35.1+/-1.25%). However, fractional shortening at the midwall was reduced in the concentric hypertrophy athletes compared with the other two groups (midwall fractional shortening: group 1, 21.9+/-1.1, group 2, 21.9+/-0.86, group 3, 18.4+/-0.96*%; P<0.05 compared with groups 1 and 2). CONCLUSION: Subjects with physiological concentric hypertrophy have depressed midwall fractional shortening. This suggests that the observed discrepancy between midwall and endocardial shortening in patients with left ventricular hypertrophy is likely to be a function of the geometry and not necessarily a reflection of pathology within the myocardium.

Baseline instantaneous wave-free ratio as a pressure-only estimation of underlying coronary flow reserve: results of the JUSTIFY-CFR Study (Joined Coronary Pressure and Flow Analysis to Determine Diagnostic Characteristics of Basal and Hyperemic Indices of Functional Lesion Severity-Coronary Flow Reserve).

BACKGROUND: Coronary flow reserve has extensive validation as a prognostic marker in coronary disease. Although pressure-only fractional flow reserve (FFR) improves outcomes compared with angiography when guiding percutaneous coronary intervention, it disagrees with coronary flow reserve classification 30% of the time. We evaluated whether baseline instantaneous wave-free ratio (iFR) could provide an improved pressure-only estimation of underlying coronary flow reserve. METHODS AND RESULTS: Invasive pressure and flow velocity were measured in 216 stenoses from 186 patients with coronary disease. The diagnostic relationship between pressure-only indices (iFR and FFR) and coronary flow velocity reserve (CFVR) was compared using correlation coefficient and the area under the receiver operating characteristic curve. iFR showed a stronger correlation with underlying CFVR (iFR-CFVR, ρ=0.68 versus FFR-CFVR, ρ=0.50; P<0.001). iFR also agreed more closely with CFVR in stenosis classification (iFR area under the receiver operating characteristic curve, 0.82 versus FFR area under the receiver operating characteristic curve, 0.72; P<0.001, for a CFVR of 2). The closer relationship between iFR and CFVR was found for different CFVR cutoffs and was particularly marked in the 0.6 to 0.9 FFR range. Hyperemic FFR flow was similar to baseline iFR flow in functionally significant lesions (FFR ≤0.75; mean FFR flow, 25.8±13.7 cm/s versus mean iFR flow, 21.5±11.7 cm/s; P=0.13). FFR flow was higher than iFR flow in nonsignificant stenoses (FFR >0.75; mean FFR flow, 42.3±22.8 cm/s versus mean iFR flow, 26.1±15.5 cm/s; P<0.001). CONCLUSIONS: When compared with FFR, iFR shows stronger correlation and better agreement with CFVR. These results provide physiological evidence that iFR could potentially be used as a functional index of disease severity, independently from its agreement with FFR.

Pre-angioplasty instantaneous wave-free ratio pullback provides virtual intervention and predicts hemodynamic outcome for serial lesions and diffuse coronary artery disease.

OBJECTIVES: The aim of this study was to perform hemodynamic mapping of the entire vessel using motorized pullback of a pressure guidewire with continuous instantaneous wave-free ratio (iFR) measurement. BACKGROUND: Serial stenoses or diffuse vessel narrowing hamper pressure wire-guided management of coronary stenoses. Characterization of functional relevance of individual stenoses or narrowed segments constitutes an unmet need in ischemia-driven percutaneous revascularization. METHODS: The study was performed in 32 coronary arteries with tandem and/or diffusely diseased vessels. An automated iFR physiological map, integrating pullback speed and physiological information, was built using dedicated software to calculate physiological stenosis severity, length, and intensity (ΔiFR/mm). This map was used to predict the best-case post-percutaneous coronary intervention (PCI) iFR (iFRexp) according to the stented location, and this was compared with the observed iFR post-PCI (iFRobs). RESULTS: After successful PCI, the mean difference between iFRexp and iFRobs was small (mean difference: 0.016 ± 0.004) with a strong relationship between ΔiFRexp and ΔiFRobs (r = 0.97, p < 0.001). By identifying differing iFR intensities, it was possible to identify functional stenosis length and quantify the contribution of each individual stenosis or narrowed segment to overall vessel stenotic burden. Physiological lesion length was shorter than anatomic length (12.6 ± 1.5 vs. 23.3 ± 1.3, p < 0.001), and targeting regions with the highest iFR intensity predicted significant improvement post-PCI (r = 0.86, p < 0.001). CONCLUSIONS: iFR measurements during continuous resting pressure wire pullback provide a physiological map of the entire coronary vessel. Before a PCI, the iFR pullback can predict the hemodynamic consequences of stenting specific stenoses and thereby may facilitate the intervention and stenting strategy.

Hemodynamic response to intravenous adenosine and its effect on fractional flow reserve assessment: results of the Adenosine for the Functional Evaluation of Coronary Stenosis Severity (AFFECTS) study.

BACKGROUND: We studied the hemodynamic response to intravenous adenosine on calculation of fractional flow reserve (FFR). Intravenous adenosine is widely used to achieve conditions of stable hyperemia for measurement of FFR. However, intravenous adenosine affects both systemic and coronary vascular beds differentially. METHODS AND RESULTS: A total of 283 patients (310 coronary stenoses) underwent coronary angiography with FFR using intravenous adenosine 140 mcg/kg per minute via a central femoral vein. Offline analysis was performed to calculate aortic (Pa), distal intracoronary (Pd), and reservoir (Pr) pressure at baseline, peak, and stable hyperemia. Seven different hemodynamic patterns were observed according to Pa and Pd change at peak and stable hyperemia. The average time from baseline to stable hyperemia was 68.2±38.5 seconds, when both ΔPa and ΔPd were decreased (ΔPa, -10.2±10.5 mm Hg; ΔPd, -18.2±10.8 mm Hg; P<0.001 for both). The fall in Pa closely correlated with the reduction in peripheral Pr (ΔPr, -12.9±15.7 mm Hg; P<0.001; r=0.9; P<0.001). ΔPa and ΔPd were closely related under conditions of peak (r=0.75; P<0.001) and stable hyperemia (r=0.83; P<0.001). On average, 56% (10.2 mm Hg) of the reduction in Pd was because of fall in Pa. FFR lesion classification changed in 9% using an FFR threshold of ≤0.80 and 5.2% with FFR threshold <0.75 when comparing Pd/Pa at peak and stable hyperemia. CONCLUSIONS: Intravenous adenosine results in variable changes in systemic blood pressure, which can lead to alterations in FFR lesion classification. Attention is required to ensure FFR is measured under conditions of stable hyperemia, although the FFR value at this point may be numerically higher.

Improvement in coronary haemodynamics after percutaneous coronary intervention: assessment using instantaneous wave-free ratio.

OBJECTIVE: To determine whether the instantaneous wave-free ratio (iFR) can detect improvement in stenosis significance after percutaneous coronary intervention (PCI) and compare this with fractional flow reserve (FFR) and whole cycle Pd/Pa. DESIGN: A prospective observational study was undertaken in elective patients scheduled for PCI with FFR ≤ 0.80. Intracoronary pressures were measured at rest and during adenosine-mediated vasodilatation, before and after PCI. iFR, Pd/Pa and FFR values were calculated using the validated fully automated algorithms. SETTING: Coronary catheter laboratories in two UK centres and one in the USA. PATIENTS: 120 coronary stenoses in 112 patients were assessed. The mean age was 63 ± 10 years, while 84% were male; 39% smokers; 33% with diabetes. Mean diameter stenosis was 68 ± 16% by quantitative coronary angiography. RESULTS: Pre-PCI, mean FFR was 0.66 ± 0.14, mean iFR was 0.75 ± 0.21 and mean Pd/Pa 0.83 ± 0.16. PCI increased all indices significantly (FFR 0.89 ± 0.07, p<0.001; iFR 0.94 ± 0.05, p<0.001; Pd/Pa 0.96 ± 0.04, p<0.001). The change in iFR after intervention (0.20 ± 0.21) was similar to ΔFFR 0.22 ± 0.15 (p=0.25). ΔFFR and ΔiFR were significantly larger than resting ΔPd/Pa (0.13 ± 0.16, both p<0.001). Similar incremental changes occurred in patients with a higher prevalence of risk factors for microcirculatory disease such as diabetes and hypertension. CONCLUSIONS: iFR and FFR detect the changes in coronary haemodynamics elicited by PCI. FFR and iFR have a significantly larger dynamic range than resting Pd/Pa. iFR might be used to objectively document improvement in coronary haemodynamics following PCI in a similar manner to FFR.

Diagnostic classification of the instantaneous wave-free ratio is equivalent to fractional flow reserve and is not improved with adenosine administration. Results of CLARIFY (Classification Accuracy of Pressure-Only Ratios Against Indices Using Flow Study).

OBJECTIVES: This study sought to determine if adenosine administration is required for the pressure-only assessment of coronary stenoses. BACKGROUND: The instantaneous wave-free ratio (iFR) is a vasodilator-free pressure-only measure of the hemodynamic severity of a coronary stenosis comparable to fractional flow reserve (FFR) in diagnostic categorization. In this study, we used hyperemic stenosis resistance (HSR), a combined pressure-and-flow index, as an arbiter to determine when iFR and FFR disagree which index is most representative of the hemodynamic significance of the stenosis. We then test whether administering adenosine significantly improves diagnostic performance of iFR. METHODS: In 51 vessels, intracoronary pressure and flow velocity was measured distal to the stenosis at rest and during adenosine-mediated hyperemia. The iFR (at rest and during adenosine administration [iFRa]), FFR, HSR, baseline, and hyperemic microvascular resistance were calculated using automated algorithms. RESULTS: When iFR and FFR disagreed (4 cases, or 7.7% of the study population), HSR agreed with iFR in 50% of cases and with FFR in 50% of cases. Differences in magnitude of microvascular resistance did not influence diagnostic categorization; iFR, iFRa, and FFR had equally good diagnostic agreement with HSR (receiver-operating characteristic area under the curve 0.93 iFR vs. 0.94 iFRa and 0.96 FFR, p = 0.48). CONCLUSIONS: iFR and FFR had equivalent agreement with classification of coronary stenosis severity by HSR. Further reduction in resistance by the administration of adenosine did not improve diagnostic categorization, indicating that iFR can be used as an adenosine-free alternative to FFR.

Classification performance of instantaneous wave-free ratio (iFR) and fractional flow reserve in a clinical population of intermediate coronary stenoses: results of the ADVISE registry.

AIMS: To evaluate the classification agreement between instantaneous wave-free ratio (iFR) and fractional flow reserve (FFR) in patients with angiographic intermediate coronary stenoses. METHODS AND RESULTS: Three hundred and twelve patients (339 stenoses) with angiographically intermediate stenoses were included in this international clinical registry. The iFR was calculated using fully automated algorithms. The receiver operating characteristic (ROC) curve was used to identify the iFR optimal cut-point corresponding to FFR 0.8. The classification agreement of coronary stenoses as significant or non-significant was established between iFR and FFR and between repeated FFR measurements for each 0.05 quantile of FFR values, from 0.2 to 1. Close agreement was observed between iFR and FFR (area under ROC curve= 86%). The optimal iFR cut-off (for an FFR of 0.80) was 0.89. After adjustment for the intrinsic variability of FFR, the classification agreement (accuracy) between iFR and FFR was 94%. Amongst the stenoses classified as non-significant by iFR (>0.89) and as significant by FFR (≤0.8), 81% had associated FFR values located within the FFR "grey-zone" (0.75-0.8) and 41% within the 0.79-0.80 FFR range. CONCLUSIONS: In a population of intermediate coronary stenoses, the classification agreement between iFR and FFR is excellent and similar to that of repeated FFR measurements in the same sample. Vasodilator-independent assessment of intermediate stenosis seems applicable and may foster adoption of coronary physiology in the catheterisation laboratory.

Hybrid iFR-FFR decision-making strategy: implications for enhancing universal adoption of physiology-guided coronary revascularisation.

AIMS: Adoption of fractional flow reserve (FFR) remains low (6-8%), partly because of the time, cost and potential inconvenience associated with vasodilator administration. The instantaneous wave-Free Ratio (iFR) is a pressure-only index of stenosis severity calculated without vasodilator drugs. Before outcome trials test iFR as a sole guide to revascularisation, we evaluate the merits of a hybrid iFR-FFR decision-making strategy for universal physiological assessment. METHODS AND RESULTS: Coronary pressure traces from 577 stenoses were analysed. iFR was calculated as the ratio between Pd and Pa in the resting diastolic wave-free window. A hybrid iFR-FFR strategy was evaluated, by allowing iFR to defer some stenoses (where negative predictive value is high) and treat others (where positive predictive value is high), with adenosine being given only to patients with iFR in between those values. For the most recent fixed FFR cut-off (0.8), an iFR of <0.86 could be used to confirm treatment (PPV of 92%), whilst an iFR value of >0.93 could be used to defer revascularisation (NPV of 91%). Limiting vasodilator drugs to cases with iFR values between 0.86 to 0.93 would obviate the need for vasodilator drugs in 57% of patients, whilst maintaining 95% agreement with an FFR-only strategy. If the 0.75-0.8 FFR grey zone is accounted for, vasodilator drug requirement would decrease by 76%. CONCLUSION: A hybrid iFR-FFR decision-making strategy for revascularisation could increase adoption of physiology-guided PCI, by more than halving the need for vasodilator administration, whilst maintaining high classification agreement with an FFR-only strategy.

Why does primary angioplasty not work in registries? Quantifying the susceptibility of real-world comparative effectiveness data to allocation bias.

BACKGROUND: Meta-analysis of registries (comparative effectiveness research) shows that primary angioplasty and fibrinolysis have equivalent real-world survival. Yet, randomized, controlled trials consistently find primary angioplasty superior. Can unequal allocation of higher-risk patients in registries have masked primary angioplasty benefit? METHODS AND RESULTS: First, we constructed a model to demonstrate the potential effect of allocation bias. We then analyzed published registries (55022 patients) for allocation of higher-risk patients (Killip class ≥1) to determine whether the choice of reperfusion therapy was affected by the risk level of the patient. Meta-regression was used to examine the relationship between differences in allocation of high-risk patient to primary angioplasty or fibrinolysis and mortality. Initial modeling suggested that registry outcomes are sensitive to allocation bias of high-risk patients. Across the registries, the therapy receiving excess high-risk patients had worse mortality. Unequal distribution of high-risk status accounted for most of the between-registry variance (adjusted R(2)(meta)=83.1%). Accounting for differential allocation of higher-risk patients, primary angioplasty gave 22% lower mortality (odds ratio, 0.78; 95% confidence interval, 0.64-0.97; P=0.029). We derive a formula, called the number needed to abolish, highlighting situations in which comparative effectiveness studies are particularly vulnerable to this bias. CONCLUSIONS: In ST-segment elevation myocardial infarction, clinicians' preference for management of a few high-risk patients can shift mortality substantially. Comparative effectiveness research in any disease is vulnerable to this, especially diseases with an immediately identifiable high-risk subgroup that clinicians prefer to allocate to 1 therapy. For this reason, preliminary indications from registry-based comparative effectiveness research should be definitively tested by randomized, controlled trials.

Attenuation of wave reflection by wave entrapment creates a "horizon effect" in the human aorta.

Wave reflection is thought to be important in the augmentation of blood pressure. However, identification of distal reflections sites remains unclear. One possible explanation for this is that wave reflection is predominately determined by an amalgamation of multiple proximal small reflections rather than large discrete reflections originating from the distal peripheries. In 19 subjects (age, 35-73 years), sensor-tipped intra-arterial wires were used to measure pressure and Doppler velocity at 10-cm intervals along the aorta, starting at the aortic root. Incident and reflected waves were identified and timings and magnitudes quantified using wave intensity analysis. Mean wave speed increased along the length of the aorta (proximal, 6.8±0.9 m/s; distal, 10.7±1.5 m/s). The incident wave was tracked moving along the aorta, taking 55±4 ms to travel from the aortic root to the distal aorta. However, the timing to the refection site distance did not differ between proximal and distal aortic measurement sites (proximal aorta, 48±5 ms versus distal aorta, 42±4 ms; P=0.3). We performed a second analysis using aortic waveforms in a nonlinear model of pulse-wave propagation. This demonstrated very similar results to those observed in vivo and also an exponential attenuation in reflection magnitude. There is no single dominant refection site in or near the distal aorta. Rather, there are multiple reflection sites along the aorta, for which the contributions are attenuated with distance. We hypothesize that rereflection of reflected waves leads to wave entrapment, preventing distal waves being seen in the proximal aorta.