Simultaneous assessment of fractional and coronary flow reserves in cardiac transplant recipients: Physiologic Investigation for Transplant Arteriopathy (PITA Study)

Is discordance of coronary flow reserve and fractional flow reserve due to methodology or clinically relevant coronary pathophysiology?

OBJECTIVES

The purpose of this study was to determine whether observed discordance between coronary flow reserve (CFR) and fractional flow reserve (FFR) is due to methodology or reflects basic coronary pathophysiology.

BACKGROUND

Despite the clinical importance of coronary physiological assessment, relationships between its 2 most common tools, CFR and FFR, remain poorly defined.

METHODS

The worst CFR and stress relative uptake were recorded from 1,500 sequential cardiac positron emission tomography cases from our center. From the literature, we assembled all combined, invasive CFR-FFR measurements, including a subset before and after angioplasty. Both datasets were compared with a fluid dynamic model of the coronary circulation predicting relationships between CFR and FFR for variable diffuse and focal narrowing.

RESULTS

A modest but significant linear relationship exists between CFR and FFR both invasively (r = 0.34, p < 0.001) and using positron emission tomography (r = 0.36, p < 0.001). Most clinical patients undergoing CFR or FFR measurements have diffusely reduced CFR consistent with diffuse atherosclerosis or small-vessel disease. The theoretical model predicts linear relationships between CFR and FFR for progressive stenosis with slopes dependent on diffuse narrowing, matching observed data. Reported changes in CFR and FFR with angioplasty agree with model predictions of removing focal stenosis but leaving diffuse disease. Although CFR-FFR concordance is common, discordance is due to dominant or absent diffuse versus focal disease, reflecting basic pathophysiology.

CONCLUSIONS

CFR is linearly related to FFR for progressive stenosis superimposed on diffuse narrowing. The relative contributions of focal and diffuse disease define the slope and values along the linear CFR and FFR relationship. Discordant CFR and FFR values reflect divergent extremes of focal and diffuse disease, not failure of either tool. With such discordance observed by invasive and noninvasive techniques and also fitting fluid dynamic predictions, it reflects clinically relevant basic coronary pathophysiology, not methodology.

Coronary flow reserve by transthoracic echocardiography predicts epicardial intimal thickening in cardiac allograft vasculopathy

Cardiac allograft vasculopathy (CAV) is the leading cause of morbidity and mortality in heart transplantation (HT). We sought to investigate the role of coronary flow reserve (CFR) by contrast-enhanced transthoracic echocardiography (CE-TTE) in CAV diagnosis. CAV was defined as maximal intimal thickness (MIT) assessed by intravascular ultrasound (IVUS) > or =0.5 mm. CFR was assessed in the left anterior descending coronary artery in 22 HT recipients at 6 +/- 4 years post-HT. CAV was diagnosed in 10 patients (group A), 12 had normal coronaries (group B). The mean MIT was 0.7 +/- 0.1 mm (range 0.03-1.8). MIT was higher in group A (1.16 +/- 0.3 mm vs. 0.34 +/- 0.07 mm, p < 0.0001). CFR was 3.1 +/- 0.8 in all patients and lower in group A (2.5 +/- 0.6 vs. 3.7 +/- 0.3, p < 0.0001). CFR was inversely related with MIT (r =-0.774, p < 0.0001). A cut point of < or =2.9, identified as optimal by receiver operating characteristics analysis was 100% specific and 80% sensitive (PPV = 100%, NPV = 89%, Accuracy = 91%). CFR assessment by CE-TTE is a novel noninvasive diagnostic tool in the detection of CAV defined as MIT > or =0.5 mm. CFR by CE-TTE may reduce the need for routine IVUS in HT.

PET assessment of myocardial perfusion reserve inversely correlates with intravascular ultrasound findings in angiographically normal cardiac transplant recipients

Cardiac allograft vasculopathy (CAV) is the major determinant of long-term survival after heart transplantation. We aimed to evaluate the efficacy of PET as a noninvasive way to assess the early stages of CAV.

METHODS

Twenty-seven consecutive patients (20 men and 7 women; mean age +/- SD, 46 +/- 12 y) who had normal results on coronary angiography and normal left ventricular systolic function (ejection fraction >or= 60%) were enrolled at 2.5 +/- 2.1 y after transplantation. Myocardial blood flow (MBF) was assessed using dynamic (13)N-ammonia PET at rest and during adenosine-induced hyperemia, and myocardial perfusion reserve (MPR) was calculated as the ratio of hyperemic MBF to resting MBF. Regional (13)N-ammonia PET was assessed using a 5-point scoring system. The intravascular ultrasound (IVUS) measurements for the extent of intimal hyperplasia, including plaque volume index (calculated as [total plaque volume/total vessel volume] x 100%) and maximum area of stenosis, were compared with MPR by linear regression analysis.

RESULTS

In 27 angiographically normal cardiac transplant recipients, MBF at rest and during adenosine stress and MPR of the left anterior descending artery distribution correlated strongly with the other 2 coronary artery distribution territories (r >or= 0.97, P < 0.0001). Summed stress score and summed difference score showed a moderate inverse correlation with MPR (r = -0.41 and -0.49, respectively; P < 0.05) but not with IVUS measurements. MPR correlated inversely with plaque volume index (r = -0.40, P < 0.05) but not with maximal luminal stenosis as assessed by IVUS. In addition, MPR and IVUS measurements gradually inversely changed after heart transplantation (all P < 0.05).

CONCLUSION

This study confirms that CAV is a progressive process, diffusely involving the epicardial and microvascular coronary system. Plaque burden as determined by IVUS agrees well with MPR as assessed by PET in recipients with normal coronary angiography results. This finding suggests that dynamic (13)N-ammonia PET is clinically feasible for the early detection of CAV and can be used as a reliable marker of disease progression.

Assessment of microcirculatory remodeling with intracoronary flow velocity and pressure measurements: validation with endomyocardial sampling in cardiac allografts

BACKGROUND

Intracoronary physiology techniques have been validated extensively for the assessment of epicardial stenoses but not for the lone study of coronary microcirculation. We performed a comparison between 4 intracoronary physiological indices with the actual structural microcirculatory changes documented in transplanted hearts.

METHODS AND RESULTS

In 17 cardiac allograft patients without coronary stenoses, ECG, intracoronary Doppler flow velocity, and aortic pressure were digitally recorded before and during maximal hyperemia with a dedicated system. Postprocessing of data yielded 4 indices of microcirculatory status: coronary flow velocity reserve (2.13+/-0.59), instantaneous hyperemic diastolic velocity pressure slope (2.33+/-1.25 cm x s x (-1)mm Hg(-1)), coronary resistance index (1.65+/-0.88 mm Hg x cm(-1) x s(-1)), and coronary resistance reserve (2.36+/-0.65). Quantitative morphometry was performed in endomyocardial biopsies during the same hospital intake; arteriolar obliteration (76.57+/-6.95%) and density (2.00+/-1.22 arterioles per 1 mm(2)) and capillary density (645+/-179 capillaries per 1 mm(2)) were measured. Univariate regression analysis between intracoronary measurements and histological findings revealed that instantaneous hyperemic diastolic velocity-pressure slope correlated with arteriolar obliteration (r=0.58, P=0.014) and capillary density (r=0.60, P=0.012). Statistical adjustment revealed an independent contribution of arteriolar obliteration (beta=0.61, P=0.0009) and capillary density (beta=-0.60, P=0.0008) to instantaneous hyperemic diastolic velocity-pressure slope values, resulting in an excellent predictive model (r=0.84, P=0.0002). Coronary resistance index correlated only with capillary density (r=0.70, P=0.019). Relative indices (coronary flow velocity reserve and coronary resistance reserve) did not correlate significantly with arteriolar obliteration, capillary density, or arteriolar density.

CONCLUSIONS

Intracoronary indices derived from pressure and flow, particularly instantaneous hyperemic diastolic velocity-pressure slope, appear to be superior to coronary flow velocity reserve in detecting structural microcirculatory changes. Both arteriolar obliteration and capillary rarefaction seem to influence microcirculatory hemodynamics independently.

Determinants of coronary flow reserve in heart transplantation: a study performed with contrast-enhanced echocardiography

BACKGROUND

Determination of coronary flow reserve (CFR) is increasingly being used in cardiac allograft vasculopathy (CAV). We aimed to identify determinants of CFR in heart transplantation (HT).

METHODS

CFR was measured by transthoracic echocardiography in 119 HT recipients (97 men, 22 women; 50 +/- 12 years of age at HT and 8 +/- 5 years post-HT). CFR was expressed as the ratio of hyperemic (adenosine infusion at a rate of 0.14 mg/kg) to basal diastolic flow velocity. Rejection scores (RS) on endomyocardial biopsy were calculated. Angiographic CAV was analyzed using a qualitative grading system. The coronary tree was divided into 17 traits and a CAV severity/diffusion index (SDI) was calculated for each patient, summing the scores assigned to all lesions.

RESULTS

Upon multivariate analysis, CFR was related to CAV (p = 0.001), interventricular septum thickness (p = 0.01), ischemic heart disease pre-HT (p = 0.02) and SDI and SDI/segment number (p < 0.0001 and p = 0.003, respectively). In patients without CAV, CFR was related only to RS for severe grades (p = 0.01).

CONCLUSIONS

Left ventricular hypertrophy, CAV and its severity/diffusion independently contribute to reduced CFR. In patients without angiographic CAV, CFR was only independently related to RS. Because a high rejection burden is associated with increased risk of CAV, CFR reduction may be an early marker of CAV. Microvascular dysfunction may contribute to the late morbidity and mortality seen in HT.

Hemodynamic diagnostics of epicardial coronary stenoses: in-vitro experimental and computational study

BACKGROUND

The severity of epicardial coronary stenosis can be assessed by invasive measurements of trans-stenotic pressure drop and flow. A pressure or flow sensor-tipped guidewire inserted across the coronary stenosis causes an overestimation in true trans-stenotic pressure drop and reduction in coronary flow. This may mask the true severity of coronary stenosis. In order to unmask the true severity of epicardial stenosis, we evaluate a diagnostic parameter, which is obtained from fundamental fluid dynamics principles. This experimental and numerical study focuses on the characterization of the diagnostic parameter, pressure drop coefficient, and also evaluates the pressure recovery downstream of stenoses.

METHODS

Three models of coronary stenosis namely, moderate, intermediate and severe stenosis, were manufactured and tested in the in-vitro set-up simulating the epicardial coronary network. The trans-stenotic pressure drop and flow distal to stenosis models were measured by non-invasive method, using external pressure and flow sensors, and by invasive method, following guidewire insertion across the stenosis. The viscous and momentum-change components of the pressure drop for various flow rates were evaluated from quadratic relation between pressure drop and flow. Finally, the pressure drop coefficient (CDPe) was calculated as the ratio of pressure drop and distal dynamic pressure. The pressure recovery factor (eta) was calculated as the ratio of pressure recovery coefficient and the area blockage.

RESULTS

The mean pressure drop-flow characteristics before and during guidewire insertion indicated that increasing stenosis causes a shift in dominance from viscous pressure to momentum forces. However, for intermediate (approximately 80%) area stenosis, which is between moderate (approximately 65%) and severe (approximately 90%) area stenoses, both losses were similar in magnitude. Therefore, guidewire insertion plays a critical role in evaluating the hemodynamic severity of coronary stenosis. More importantly, mean CDPe increased (17 +/- 3.3 to 287 +/- 52, n = 3, p < 0.01) and mean eta decreased (0.54 +/- 0.04 to 0.37 +/- 0.05, p < 0.01) from moderate to severe stenosis during guidewire insertion.

CONCLUSION

The wide range of CDPe is not affected that much by the presence of guidewire. CDPe can be used in clinical practice to evaluate the true severity of coronary stenosis due to its significant difference between values measured at moderate and severe stenoses.

Impact of coronary endothelial dysfunction on adverse long-term outcome after heart transplantation

BACKGROUND

Coronary vasomotor dysfunction is a common finding in cardiac transplant recipients and is an early marker for the development of graft atherosclerosis. The present prospective study tested whether endothelial dysfunction independently predicts cardiovascular-related events and death after heart transplantation (HTx).

METHODS

Functional and structural coronary changes were evaluated in 185 consecutive patients 25+/-33 months after HTx. The following potential risk factors for graft survival were assessed at baseline: hypertension, diabetes, dyslipidemia, donor and recipient characteristics (age, gender, cytomegalovirus-infection, human leukocyte antigen-mismatch), pretransplantation diagnosis, ischemic time, treated rejection episodes, immunosuppressive regimens, and medication.The prespecified prospectively defined endpoints were cardiovascular-related events with progressive heart failure, acute myocardial infarction, coronary revascularization, retransplantation, and death. Patients were followed-up for 60+/-17 months.

RESULTS

Event-free survival for the entire group was 73% (25 cardiovascular-related events, 25 deaths). Using multivariate analysis, epicardial endothelial dysfunction (relative risk [RR] 1.97; P=0.028), angiographic cardiac allograft vasculopathy (RR 2.11; P=0.023), diabetes (RR 2.32; P=0.022), high serum levels of CyA (RR 3.54; P=0.006) and Tac (RR 6.82; P=0.002), uncommon reasons for transplantation (RR 4.69; P=0.002), and the absence of statin therapy (RR 0.33; P=0.025) were detected as independent predictors of cardiovascular-related events and death.

CONCLUSION

This is the first study showing that epicardial endothelial dysfunction independently predicts outcome in HTx patients providing functional and prognostic information that complete angiographic risk factor assessment.

Coronary flow reserve measurement detects transplant coronary artery disease in pediatric heart transplant patients

BACKGROUND

Cardiac allograft vasculopathy (CAV) in patients who have undergone heart transplantation leads to graft dysfunction and is still the major concern for long-term survival. Evaluation of coronary flow velocity reserve (CFR) has been established for diagnosis of CAV. Systemic application of adenosine vs intracoronary testing for CFR has been validated in adults; however, its accuracy in pediatric patients has not yet been proven.

METHODS

CFR was prospectively measured in 33 clinically asymptomatic pediatric heart transplant recipients. CFR measurements were made in the left anterior descending (LAD) artery using a 0.014-inch Doppler FloWire (Cardiometrics). CFR was defined as the ratio of hyperemic (after adenosine injection) to basal (before adenosine) average peak velocity (APV). Adenosine (Adrekar) was administered by intracoronary (15 or 30 mug bolus) and systemic (0.1 mg/kg) injection in each patient. Epicardial CAV was evaluated in coronary angiograms (Stanford criteria) and microvasculopathy was diagnosed in endomyocardial biopsies (evidence of luminal stenosis) blinded to clinical data.

RESULTS

Thirty-three patients were included in this study. Their median age (range) was 11.9 (1.4 to 17) years and median post-transplant time 4.3 (1 to 11.7) years. Seventeen of the 33 patients had epicardial CAV (mainly peripheral obliterations or B1 and B2 lesions) and microvascular CAV. Epicardial CAV only was found in 4 patients and microvasculopathy only was present in only 1 patient. CFR was significantly reduced in patients with epicardial CAV and microvasculopathy when compared with patients without any signs of CAV: 206 +/- 53 vs 276 +/- 39 (p < 0.001) for the systemic application and 213 +/- 50 vs 271 +/- 45 (p = 0.004) for the intracoronary application.

CONCLUSIONS

CFR and coronary vasoreactivity to adenosine are decreased in pediatric patients with CAV and correlate with histopathologic and angiographic evidence of microvascular disease. Measurement of CFR with intracoronary and systemic application of adenosine is comparable, while systemic application is necessary for non-invasive measurement of CFR in pediatric patients.

A review of methods for assessment of coronary microvascular disease in both clinical and experimental settings

Obstructive disease of the large coronary arteries is the prominent cause for angina pectoris. However, angina may also occur in the absence of significant coronary atherosclerosis or coronary artery spasm, especially in women. Myocardial ischaemia in these patients is often associated with abnormalities of the coronary microcirculation and may thus represent a manifestation of coronary microvascular disease (CMD). Elucidation of the role of the microvasculature in the genesis of myocardial ischaemia and cardiac damage-in the presence or absence of obstructive coronary atherosclerosis-will certainly result in more rational diagnostic and therapeutic interventions for patients with ischaemic heart disease. Specifically targeted research based on improved assessment modalities is needed to improve the diagnosis of CMD and to translate current molecular, cellular, and physiological knowledge into new therapeutic options.

Cardiac allograft vasculopathy: recent developments

Cardiac allograft vasculopathy (CAV) continues to limit the long-term success of cardiac transplantation. Recent insights have underscored the fact that innate and adaptive immune responses are involved in the pathogenesis of CAV. Vascular lesions are the result of cumulative endothelial injuries induced both by alloimmune responses and by nonspecific insults (including ischemia-reperfusion injury, viral infections, and metabolic disorders) in the context of impaired repair mechanisms. Intravascular ultrasound is the most sensitive method for detection of CAV, and progressive intimal thickening in the first posttransplant year identifies patients at high risk for future cardiovascular events. Encouraging results with regard to the detection of CAV by noninvasive methods should be an incentive to apply routine noninvasive imaging during mid- to long-term follow-up. Improved immunosuppressive drugs, including mycophenolate mofetil and proliferation signal inhibitors, as well as statins (in part via immunomodulation), have beneficial effects on CAV progression, although there is still a need to confirm the impact of vasodilators in improving outcome after heart transplantation. Coronary revascularization for CAV is only palliative, with no long-term survival benefit. Three main strategies for CAV prevention are currently under investigation: inhibition of growth factors and cytokines, cell therapy, and tolerance induction. However, because individual responses to an allograft change over time, assays to monitor the recipient's immune response and individualized methods for therapeutic immune modulation are clearly needed.

Effect of rapamycin therapy on coronary artery physiology early after cardiac transplantation

BACKGROUND

Rapamycin has been shown to reduce anatomical evidence of cardiac allograft vasculopathy, but its effect on coronary artery physiology is unknown.

METHODS

Twenty-seven patients without angiographic evidence of coronary artery disease underwent measurement of fractional flow reserve (FFR), coronary flow reserve (CFR), and the index of microcirculatory resistance (IMR) within 8 weeks and then 1 year after transplantation using a pressure sensor/thermistor-tipped guidewire. Measurements were compared between consecutive patients who were on rapamycin for at least 3 months during the first year after transplantation (rapamycin group, n = 9) and a comparable group on mycophenolate mofetil (MMF) instead (MMF group, n = 18).

RESULTS

At baseline, there was no significant difference in FFR, CFR, or IMR between the 2 groups. At 1 year, FFR declined significantly in the MMF group (0.87 +/- 0.06 to 0.82 +/- 0.06, P = .009) but did not change in the rapamycin group (0.91 +/- 0.05 to 0.89 +/- 0.04, P = .33). Coronary flow reserve and IMR did not change significantly in the MMF group (3.1 +/- 1.7 to 3.2 +/- 1.0, P = .76; and 27.5 +/- 18.1 to 19.1 +/- 7.6, P = .10, respectively) but improved significantly in the rapamycin group (2.3 +/- 0.8 to 3.8 +/- 1.4, P < .03; and 27.0 +/- 11.5 to 17.6 +/- 7.5, P < .03, respectively). Multivariate regression analysis revealed that rapamycin therapy was an independent predictor of CFR and FFR at 1 year after transplantation.

CONCLUSION

Early after cardiac transplantation, rapamycin therapy is associated with improved coronary artery physiology involving both the epicardial vessel and the microvasculature.

Rationale and design of the Fractional Flow Reserve versus Angiography for Multivessel Evaluation (FAME) study

BACKGROUND

Although its limitations for diagnosing critical coronary artery disease are well described, coronary angiography remains the predominant method for guiding decisions about stent implantation in patients with multivessel coronary artery disease. However, some have suggested that invasive physiologic guidance may improve decision making.

TRIAL DESIGN

The objective of this multicenter, randomized clinical trial is to compare the efficacy of 2 strategies, one based on angiographic guidance to one based on physiologic guidance with fractional flow reserve (FFR), for deciding which coronary lesions to stent in patients with multivessel coronary disease. Eligible patients must have coronary narrowings > 50% diameter stenosis in > or = 2 major epicardial vessels, > or = 2 of which the investigator feels require drug-eluting stent placement. Patients with previous coronary bypass surgery or left main coronary disease are excluded. Based on angiographic evaluation, the investigator notes the lesions that require stenting. The patient is then randomly assigned to either angiographic guidance or FFR guidance. Patients assigned to angiographic guidance undergo stenting as planned. Patients assigned to FFR guidance first have FFR measured in each diseased vessel and only undergo stenting if the FFR is < or = 0.80. The primary end point of the study is a composite of major adverse cardiac events, including death, myocardial infarction, and repeat coronary revascularization, at 1 year. Secondary end points will include the individual adverse events, cost-effectiveness, quality of life, and 30-day, 6-month, 2-year, and 5-year outcomes.

CONCLUSION

The FAME study will examine for the first time in a large, multicenter, randomized fashion the role of measuring FFR in patients undergoing multivessel percutaneous coronary intervention.

Changes in coronary anatomy and physiology after heart transplantation

Cardiac allograft vasculopathy (CAV) is a progressive process involving the epicardial and microvascular coronary systems. The timing of the development of abnormalities in these 2 compartments and the correlation between changes in physiology and anatomy are undefined. The invasive evaluation of coronary artery anatomy and physiology with intravascular ultrasound, fractional flow reserve, coronary flow reserve, and the index of microcirculatory resistance (IMR) was performed in the left anterior descending coronary artery during 151 angiographic evaluations of asymptomatic heart transplant recipients from 0 to >5 years after heart transplantation (HT). There was no angiographic evidence of significant CAV, but during the first year after HT, fractional flow reserve decreased significantly (0.89 +/- 0.06 vs 0.85 +/- 0.07, p = 0.001), and percentage plaque volume derived by intravascular ultrasound increased significantly (15.6 +/- 7.7% to 22.5 +/- 12.3%, p = 0.0002), resulting in a significant inverse correlation between epicardial physiology and anatomy (r = -0.58, p <0.0001). The IMR was lower in these patients compared with those > or =2 years after HT (24.1 +/- 14.3 vs 29.4 +/- 18.8 units, p = 0.05), suggesting later spread of CAV to the microvasculature. As the IMR increased, fractional flow reserve increased (0.86 +/- 0.06 to 0.90 +/- 0.06, p = 0.0035 comparing recipients with IMRs < or =20 to those with IMRs > or =40), despite no difference in percentage plaque volume (21.0 +/- 11.2% vs 20.5 +/- 10.5%, p = NS). In conclusion, early after HT, anatomic and physiologic evidence of epicardial CAV was found. Later after HT, the physiologic effect of epicardial CAV may be less, because of increased microvascular dysfunction.

Coronary flow velocity pattern and coronary flow reserve by contrast-enhanced transthoracic echocardiography predict long-term outcome in heart transplantation

BACKGROUND

We assessed coronary flow velocity pattern and coronary flow reserve (CFR) by contrast-enhanced transthoracic echocardiography (CE-TTE) as markers of major adverse cardiac events (MACE) related to cardiac allograft vasculopathy (CAV) after heart transplantation (HT).

METHODS AND RESULTS

Deceleration time of diastolic flow velocity (DDT) and CFR were measured in the left anterior descending coronary artery (LAD) by CE-TTE in 66 consecutive HT patients (follow-up 19+/-5 months). CFR was calculated as the ratio of hyperemic to basal diastolic flow velocity. Angiographies were analyzed by a qualitative grading system; CAV was defined as changes grade II or higher. MACE were cardiac death, stent implantation, and heart failure. Patients with MACE had higher CAV incidence (P=0.004) and grade (P=0.008), shorter DDT (P=0.006), and lower CFR (P=0.008). A receiver-operating characteristic-derived DDT cutpoint < or = 840 ms (area under the curve 0.793; P=0.01) was 75% specific and 86% sensitive for predicting MACE, with positive predictive value (PPV) and negative predictive value (NPV) of 33% and 97%, respectively (P=0.002). A CFR cutpoint of < or =2.6 (area under the curve 0.746; P=0.01) was 62% specific and 91% sensitive for predicting MACE (PPV =32%, NPV =97%) (P=0.001). Patients with CFR < or = 2.6 and patients with DDT < or = 840 ms had a lower survival free from MACE (P=0.006 and P=0.009, respectively). By Cox regression, only a lower CFR predicted the risk of MACE (relative risk 3.1; 95% CI, 1.26 to 7.9; P=0.01).

CONCLUSIONS

In HT patients, shorter DDT and lower CFR by CE-TTE are reliable markers for CAV-related MACE. CFR is the main independent predictor of MACE.

Discordant changes in epicardial and microvascular coronary physiology after cardiac transplantation: Physiologic Investigation for Transplant Arteriopathy II (PITA II) study

BACKGROUND

Investigating changes in coronary physiology that occur after cardiac transplantation has been challenging. Simultaneous and independent assessment of the epicardial artery by measuring fractional flow reserve (FFR) and of the microvasculature by calculating the index of microvascular resistance (IMR) with a single coronary pressure wire may be useful.

METHODS

Twenty-five asymptomatic patients with normal coronary angiograms underwent FFR, thermodilution-derived IMR and coronary flow reserve (CFR) and intravascular ultrasound (IVUS) evaluation soon after cardiac transplantation and 1 year later.

RESULTS

FFR significantly worsened (0.90 +/- 0.05 at baseline to 0.85 +/- 0.06 at 1 year, p = 0.004). FFR correlated strongly with percent plaque volume as measured by IVUS (r = -0.58, p < 0.0001). IMR improved significantly (29.2 +/- 15.9 at baseline to 19.3 +/- 7.6 units at 1 year, p = 0.007). CFR increased, but not significantly (2.6 +/- 1.4 at baseline to 3.2 +/- 1.2 at 1 year, p = not significant). Diabetes and donor heart ischemic time independently predicted baseline IMR. Treatment with rapamycin independently predicted FFR at 1 year.

CONCLUSIONS

New coronary physiologic measures, FFR and IMR, show that epicardial artery physiology worsens and correlates with anatomic changes, whereas microvascular physiology improves during the first year after cardiac transplantation. CFR, the traditional method for evaluating coronary circulatory physiology, did not identify these changes.

Coronary flow reserve by contrast-enhanced echocardiography: a new noninvasive diagnostic tool for cardiac allograft vasculopathy

Noninvasive tests have proven unsatisfactory in cardiac allograft vasculopathy (CAV) diagnosis. We assessed coronary flow reserve (CFR) by contrast-enhanced transthoracic echocardiography (CE-TTE) in heart transplantation (HT). CFR was assessed in the left anterior descending coronary artery in 73 HT recipients (59 male, aged 50+/-12 years at HT), at 8+/-4.5 years post-HT. CFR measurements were taken blindly from coronary angiographies. CFR cut points were the standard value of <or=2 and those defined by receiver operating characteristics (ROC) curve analysis. CFR was lower in patients with CAV (2.3+/-0.7 vs. 3.2+/-0.5, p<0.0001). The <or=2 cut point was 100% specific and 38% sensitive. The <or=2.7 cut point, optimal by ROC analysis, was 87% specific and 82% sensitive. Accuracy rose from 71% with the standard<or=2 cut point to 85% with the optimal cut point of <or=2.7. CFR by CE-TTE may offer promise as a novel, easily repeatable and accurate noninvasive tool in CAV detection. However, further longitudinal studies in larger patient cohorts are warranted before widespread adoption can be advocated.

Invasive assessment of the coronary microcirculation: superior reproducibility and less hemodynamic dependence of index of microcirculatory resistance compared with coronary flow reserve

BACKGROUND

A simple, reproducible invasive method for assessing the coronary microcirculation is lacking. A novel index of microcirculatory resistance (IMR) has been shown in animals to correlate with true microvascular resistance and, unlike coronary flow reserve (CFR), to be independent of the epicardial artery. We sought to compare the reproducibility and hemodynamic dependence of IMR with CFR in humans.

METHODS AND RESULTS

Using a pressure-temperature sensor-tipped coronary wire, thermodilution-derived CFR and IMR were measured, along with fractional flow reserve (FFR), in 15 coronary arteries (15 patients) under the following hemodynamic conditions: (1) twice at baseline; (2) during right ventricular pacing at 110 bpm; (3) during intravenous infusion of nitroprusside; and (4) during intravenous dobutamine infusion. Mean CFR did not change during baseline measurements or during nitroprusside infusion but decreased during pacing (from 3.1+/-1.1 at baseline to 2.3+/-1.2 during pacing, P<0.05) and during dobutamine infusion (from 3.0+/-1.0 to 1.7+/-0.6 with dobutamine, P<0.0001). By comparison, mean values for IMR and FFR remained similar throughout all hemodynamic conditions. The mean coefficient of variation between 2 baseline measurements was significantly lower for IMR (6.9+/-6.5%) and FFR (1.6+/-1.6%) than for CFR (18.6+/-9.6%; P<0.01). Mean correlation between baseline measurements and each hemodynamic intervention was superior for IMR (r=0.90+/-0.05) and FFR (r=0.86+/-0.12) compared with CFR (r=0.70+/-0.05; P<0.05).

CONCLUSIONS

Compared with CFR, IMR provides a more reproducible assessment of the microcirculation, which is independent of hemodynamic perturbations. Simultaneous measurement of FFR and IMR may provide a comprehensive and specific assessment of coronary physiology at both epicardial and microvascular levels, respectively.

Characterizing momentum change and viscous loss of a hemodynamic endpoint in assessment of coronary lesions

Myocardial fractional flow reserve (FFR(myo)) and coronary flow reserve (CFR), measured with guidewire, and quantitative angiography (QA) are widely used in combination to distinguish ischemic from non-ischemic coronary stenoses. Recent studies have shown that simultaneous measurements of FFR(myo) and CFR are recommended to dissociate conduit epicardial coronary stenoses from distal resistance microvascular disease. In this study, a more comprehensive diagnostic parameter, named as lesion flow coefficient, c, is proposed. The coefficient, c, which accounts for mean pressure drop, Delta p, mean coronary flow, Q, and percentage area stenosis, can be used to assess the hemodynamic severity of a coronary artery stenoses. Importantly, the contribution of viscous loss and loss due to momentum change for several lesion sizes can be distinguished using c. FFR(myo), CFR and c were calculated for pre-angioplasty, intermediate and post-angioplasty epicardial lesions, without microvascular disease. While hyperemic c decreased from 0.65 for pre-angioplasty to 0.48 for post-angioplasty lesion with guidewire of size 0.35 mm, FFR(myo) increased from 0.52 to 0.87, and CFR increased from 1.72 to 3.45, respectively. Thus, reduced loss produced by momentum change due to lower percentage area stenosis decreased c. For post-angioplasty lesion, c decreased from 0.55 to 0.48 with the insertion of guidewire. Hence, increased viscous loss due to the presence of guidewire decreased c compared with a lesion without guidewire. Further, c showed a linear relationship with FFR(myo), CFR and percentage area stenosis for pre-angioplasty, intermediate and post-angioplasty lesion. These baseline values of c were developed from fluid dynamics fundamentals for focal lesions, and provided a single hemodynamic endpoint to evaluate coronary stenosis severity.

Microvascular Resistance Is Not Influenced by Epicardial Coronary Artery Stenosis Severity

Background— The effect of epicardial artery stenosis on myocardial microvascular resistance remains controversial. Recruitable collateral flow, which may affect resistance, was not incorporated into previous measurements.

Methods and Results— In an open-chest pig model, distal coronary pressure was measured with a pressure wire, and the apparent minimal microvascular resistance was calculated during peak hyperemia as pressure divided by flow, measured either with a flow probe around the coronary artery (R micro app ) or with a novel thermodilution technique (apparent index of microcirculatory resistance [IMR app ]). These apparent resistances were compared with the actual R micro and IMR after the coronary wedge pressure and collateral flow were incorporated into the calculation. Measurements were made at baseline (no stenosis) and after creation of moderate and severe epicardial artery stenoses. In 6 pigs, 189 measurements of R micro and IMR were made under the various epicardial artery conditions. Without consideration of collateral flow, R micro app (0.43±0.12 to 0.46±0.10 to 0.51±0.11 mm Hg/mL per minute) and IMR app (14±4 to 17±7 to 20±10 U) increased progressively and significantly with increasing epicardial artery stenosis ( P <0.001 for both). With the incorporation of collateral flow, neither R micro nor IMR increased as a result of increasing epicardial artery stenosis.

Conclusions— After collateral flow is taken into account, the minimum achievable microvascular resistance is not affected by increasing epicardial artery stenosis.

Comparison of Coronary Thermodilution and Doppler Velocity for Assessing Coronary Flow Reserve

BACKGROUND

Thermodilution coronary flow reserve (CFRthermo) is a new technique for invasively measuring coronary flow reserve (CFR) with a coronary pressure wire and is based on the ability of the pressure transducer to also measure temperature changes. Whether CFRthermo correlates well enough with absolute flow-derived CFR (CFRflow) to replace Doppler wire-derived CFR (CFRDoppler) remains unclear.

METHODS AND RESULTS

In an open-chest pig model, CFRthermo was measured in the left anterior descending (LAD) artery and compared with CFRDoppler and CFRflow, measured with an external flow probe placed around the LAD. In 9 pigs, CFR was measured simultaneously by all 3 means in the normal LAD and after creation of an epicardial LAD stenosis. To determine the added effect of microvascular disease, measurements of flow reserve were also performed after disruption of the coronary microcirculation with embolized microspheres. Intracoronary papaverine (20 mg) was used to induce hyperemia. In a total of 61 paired measurements, CFRthermo correlated strongly with the reference standard CFRflow (r=0.85, P<0.001). CFRDoppler correlated less well with CFRflow (r=0.72, P<0.001). Bland-Altman analysis showed a closer agreement between CFRthermo and CFRflow.

CONCLUSIONS

CFRthermo correlates better with CFRflow than does CFRDoppler.