Quantitative relationship between the extent and morphology of coronary atherosclerotic plaque and downstream myocardial perfusion

Stress Testing After Complete and Successful Coronary Revascularization

BACKGROUND

Noninvasive stress tests play a determinant role in the initial management of patients with chronic angina. Nonetheless, their use in the same patient population is considered inappropriate within 2 years after percutaneous coronary intervention (PCI). Indeed, early abnormal results correlate less well with angiographic control and are attributed to a number of confounding factors. We prospectively assessed prevalence and impact on the quality of life of abnormal stress test results in a highly selected patient population.

METHODS

Patients with no cardiac comorbidities who underwent successful and complete PCI with stenting for typical angina and had an abnormal exercise stress test (EST) under guideline-directed medical treatment were administered the Seattle Angina Questionnaire (SAQ). Clinical evaluation, EST, and the SAQ were repeated at 1, 6, and 12 months after the index PCI.

RESULTS

One hundred ninety-eight patients qualified and were included in the study (mean age, 64 years; 79% men). Although the majority had normal EST results or an increased threshold to angina, at 1 month after the index PCI, 29% of patients still had an abnormal result. At 6 and 12 months, 31% and 29% of patients had abnormal results, respectively. Quality-of-life assessment by the SAQ showed consistent results, with persistent angina in one third of patients. Control angiography documented a critical lesion, attributable to in-stent coronary restenosis, in only 8% of patients.

CONCLUSIONS

When stress testing is systematically performed after PCI, the prevalence of abnormal results is high and is associated with impaired quality of life. Prognostic significance along with the underlying pathophysiological mechanisms of such findings should be investigated.

Automated Quantitative Plaque Burden from Coronary CT Angiography Noninvasively Predicts Hemodynamic Significance by using Fractional Flow Reserve in Intermediate Coronary Lesions

PURPOSE

To evaluate the utility of multiple automated plaque measurements from coronary computed tomographic (CT) angiography in determining hemodynamic significance by using invasive fractional flow reserve (FFR) in patients with intermediate coronary stenosis.

MATERIALS AND METHODS

The study was approved by the institutional review board. All patients provided written informed consent. Fifty-six intermediate lesions (with 30%-69% diameter stenosis) in 56 consecutive patients (mean age, 62 years; range, 46-88 years), who subsequently underwent invasive coronary angiography with assessment of FFR (values ≤0.80 were considered hemodynamically significant) were analyzed at coronary CT angiography. Coronary CT angiography images were quantitatively analyzed with automated software to obtain the following measurements: volume and burden (plaque volume × 100 per vessel volume) of total, calcified, and noncalcified plaque; low-attenuation (<30 HU) noncalcified plaque; diameter stenosis; remodeling index; contrast attenuation difference (maximum percent difference in attenuation per unit area with respect to the proximal reference cross section); and lesion length. Logistic regression adjusted for potential confounding factors, receiver operating characteristics, and integrated discrimination improvement were used for statistical analysis.

RESULTS

FFR was 0.80 or less in 21 (38%) of the 56 lesions. Compared with nonischemic lesions, ischemic lesions had greater diameter stenosis (65% vs 52%, P = .02) and total (49% vs 37%, P = .0003), noncalcified (44% vs 33%, P = .0004), and low-attenuation noncalcified (9% vs 4%, P < .0001) plaque burden. Calcified plaque and remodeling index were not significantly different. In multivariable analysis, only total, noncalcified, and low-attenuation noncalcified plaque burden were significant predictors of ischemia (P < .015). For predicting ischemia, the area under the receiver operating characteristics curve was 0.83 for total plaque burden versus 0.68 for stenosis (P = .04).

CONCLUSION

Compared with stenosis grading, automatic quantification of total, noncalcified, and low-attenuation noncalcified plaque burden substantially improves determination of lesion-specific hemodynamic significance by FFR in patients with intermediate coronary lesions.

Prediction of left main or 3-vessel disease using myocardial perfusion reserve on dynamic thallium-201 single-photon emission computed tomography with a semiconductor gamma camera

BACKGROUND

Myocardial perfusion imaging (MPI) may fail to detect balanced ischemia. We evaluated myocardial perfusion reserve (MPR) using Tl dynamic single-photon emission computed tomography (SPECT) and a novel cadmium zinc telluride (CZT) camera for predicting 3-vessel or left main coronary artery disease (CAD). METHODS AND RESULTS: A total of 55 consecutive patients with suspected CAD underwent SPECT-MPI and coronary angiography. The MPR index was calculated using the standard 2-compartment kinetic model. We analyzed the utility of MPR index, other SPECT findings, and various clinical variables. On multivariate analysis, MPR index and history of previous myocardial infarction (MI) predicted left main and 3-vessel disease. The area under the receiver operating characteristic curve was 0.81 for MPR index, 0.699 for history of previous MI, and 0.86 for MPR index plus history of previous MI. MPR index ≤1.5 yielded the highest diagnostic accuracy. Sensitivity, specificity, and accuracy were 86%, 78%, and 80%, respectively, for MPR index, 64%, 76%, 73% for previous MI, and 57%, 93%, and 84% for MPR index plus history of previous MI.

CONCLUSIONS

Quantification of MPR using dynamic SPECT and a novel CZT camera may identify balanced ischemia in patients with left main or 3-vessel disease.

Coronary flow reserve estimated by positron emission tomography to diagnose significant coronary artery disease and predict cardiac events

Coronary artery disease (CAD) is a major cause of death in Japan. Coronary angiography is useful to assess the atherosclerotic burden in CAD patients, but its ability to predict whether patients will respond favorably to optimal medical therapy and revascularization is limited. The measurement of the fractional flow reserve with angiography is a well-validated method for identifying ischemic vessels. However, neither an anatomical assessment nor a functional assessment can delineate microvasculature or estimate its function. The quantitative coronary flow reserve (CFR) estimated from sequential myocardial perfusion images obtained by positron emission tomography (PET) during stress provides an accurate index of hyperemic reactivity to vasodilatory agents in the myocardium. In fact, there is growing evidence that the CFR reflects disease activity in the entire coronary circulation, including epicardial coronary artery stenosis, diffuse atherosclerosis, and microvascular dilatory function. Importantly, reduced CFR is observed even in patients without flow-limiting coronary stenosis, and its evaluation can improve the risk stratification of patients at any stage of CAD. This review focuses on the application of CFR estimated by cardiac PET for the diagnosis and risk stratification of patients with CAD.

Improved spillover correction model to quantify myocardial blood flow by 11C-acetate PET: comparison with 15O-H 2O PET

OBJECTIVE

(11)C-acetate has been applied for evaluation of myocardial oxidative metabolism and can simultaneously estimate myocardial blood flow (MBF). We developed a new method using two-parameter spillover correction to estimate regional MBF (rMBF) with (11)C-acetate PET in reference to MBF derived from (15)O-H2O PET. The usefulness of our new approach was evaluated compared to the conventional method using one-parameter spillover correction.

METHODS

Sixty-three subjects were examined with (11)C-acetate and (15)O-H2O dynamic PET at rest. Inflow rate of (11)C-acetate (K1) was compared with MBF derived from (15)O-H2O PET. For the derivation, the relationship between K1 and MBF from (15)O-H2O was linked by the Renkin-Crone model in 20 subjects as a pilot group. One-parameter and two-parameter corrections were applied to suppress the spillover between left ventricular (LV) wall and LV cavity. Validation was set using the other 43 subjects' data. Finally, rMBFs were calculated using relational expression derived from the pilot-group data.

RESULTS

The relationship between K1 and MBF derived from (15)O-H2O PET was approximated as K1 = [1-0.764 × exp(-1.001/MBF)] MBF from the pilot data using the two-parameter method. In the validation set, the correlation coefficient between rMBF from (11)C-acetate and (15)O-H2O demonstrated a significantly higher relationship with the two-parameter spillover correction method than the one-parameter spillover correction method (r = 0.730, 0.592, respectively, p < 0.05).

CONCLUSION

In (11)C-acetate PET study, the new two-parameter spillover correction method dedicated more accurate and robust myocardial blood flow than the conventional one-parameter method.

Prognostic Value of Nonobstructive and Obstructive Coronary Artery Disease Detected by Coronary Computed Tomography Angiography to Identify Cardiovascular Events

Background—

The contribution of plaque extent to predict cardiovascular events among patients with nonobstructive and obstructive coronary artery disease (CAD) is not well defined. Our objective was to evaluate the prognostic value of plaque extent detected by coronary computed tomography angiography.

Methods and Results—

All consecutive patients without prior CAD referred for coronary computed tomography angiography to evaluate for CAD were included. Examination findings were classified as normal, nonobstructive (<50% stenosis), or obstructive (≥50%). Based on the number of segments with disease, extent of CAD was classified as nonextensive (≤4 segments) or extensive (>4 segments). The cohort included 3242 patients followed for the primary outcome of cardiovascular death or myocardial infarction for a median of 3.6 (2.1–5.0) years. In a multivariable analysis, the presence of extensive nonobstructive CAD (hazard ratio, 3.1; 95% confidence interval, 1.5–6.4), nonextensive obstructive (hazard ratio, 3.0; 95% confidence interval, 1.3–6.9), and extensive obstructive CAD (hazard ratio, 3.9; 95% confidence interval, 2.2–7.2) were associated with an increased rate of events, whereas nonextensive, nonobstructive CAD was not. The addition of plaque extent to a model that included clinical probability as well as the presence and severity of CAD improved risk prediction.

Conclusions—

Among patients with nonobstructive CAD, those with extensive plaque experienced a higher rate of cardiovascular death or myocardial infarction, comparable with those who have nonextensive disease. Even among patients with obstructive CAD, greater extent of nonobstructive plaque was associated with higher event rate. Our findings suggest that regardless of whether obstructive or nonobstructive disease is present, the extent of plaque detected by coronary computed tomography angiography enhances risk assessment.

Preserved coronary flow reserve effectively excludes high-risk coronary artery disease on angiography

Myocardial perfusion imaging has limited sensitivity for the detection of high-risk coronary artery disease (CAD). We tested the hypothesis that a normal coronary flow reserve (CFR) would be helpful for excluding the presence of high-risk CAD on angiography.

METHODS

We studied 290 consecutive patients undergoing (82)Rb PET within 180 d of invasive coronary angiography. High-risk CAD on angiography was defined as 2-vessel disease (≥ 70% stenosis), including the proximal left anterior descending artery; 3-vessel disease; or left main CAD (≥ 50% stenosis). Patients with prior Q wave myocardial infarction, elevated troponin levels between studies, prior coronary artery bypass grafting, a left ventricular ejection fraction of less than 40%, or severe valvular heart disease were excluded.

RESULTS

Fifty-five patients (19%) had high-risk CAD on angiography. As expected, the trade-off between the sensitivity and the specificity of the CFR for identifying high-risk CAD varied substantially depending on the cutoff selected. In multivariable analysis, a binary CFR of less than or equal to 1.93 provided incremental diagnostic information for the identification of high-risk CAD beyond the model with the Duke clinical risk score (>25%), percentage of left ventricular ischemia (>10%), transient ischemic dilation index (>1.07), and change in the left ventricular ejection fraction during stress (<2) (P = 0.0009). In patients with normal or slightly to moderately abnormal results on perfusion scans (<10% of left ventricular mass) during stress (n = 136), a preserved CFR (>1.93) excluded high-risk CAD with a high sensitivity (86%) and a high negative predictive value (97%).

CONCLUSION

A normal CFR has a high negative predictive value for excluding high-risk CAD on angiography. Although an abnormal CFR increases the probability of significant obstructive CAD, it cannot reliably distinguish significant epicardial stenosis from nonobstructive, diffuse atherosclerosis or microvascular dysfunction.

Automated quantitative coronary computed tomography correlates of myocardial ischaemia on gated myocardial perfusion SPECT

PURPOSE

Automated software tools have permitted more comprehensive, robust and reproducible quantification of coronary stenosis, plaque burden and plaque location of coronary computed tomography angiography (CTA) data. The association between these quantitative CTA (QCT) parameters and the presence of myocardial ischaemia has not been explored. The aim of the present investigation was to evaluate the association between QCT parameters of coronary artery lesions and the presence of myocardial ischaemia on gated myocardial perfusion single-photon emission CT (SPECT).

METHODS

Included in the study were 40 patients (mean age 58.2 ± 10.9 years, 27 men) with known or suspected coronary artery disease (CAD) who had undergone multidetector row CTA and gated myocardial perfusion SPECT within 6 months. From the CTA datasets, vessel-based and lesion-based visual analyses were performed. Consecutively, lesion-based QCT was performed to assess plaque length, plaque burden, percentage lumen area stenosis and remodelling index. Subsequently, the presence of myocardial ischaemia was assessed using the summed difference score (SDS ≥2) on gated myocardial perfusion SPECT.

RESULTS

Myocardial ischaemia was seen in 25 patients (62.5%) in 37 vascular territories. Quantitatively assessed significant stenosis and quantitatively assessed lesion length were independently associated with myocardial ischaemia (OR 7.72, 95% CI 2.41-24.7, p < 0.001, and OR 1.07, 95% CI 1.00-1.45, p = 0.032, respectively) after correcting for clinical variables and visually assessed significant stenosis. The addition of quantitatively assessed significant stenosis (χ(2) = 20.7) and lesion length (χ(2) = 26.0) to the clinical variables and the visual assessment (χ(2) = 5.9) had incremental value in the association with myocardial ischaemia.

CONCLUSION

Coronary lesion length and quantitatively assessed significant stenosis were independently associated with myocardial ischaemia. Both quantitative parameters have incremental value over baseline variables and visually assessed significant stenosis. Potentially, QCT can refine assessment of CAD, which may be of potential use for identification of patients with myocardial ischaemia.

Prognostic interplay of coronary artery calcification and underlying vascular dysfunction in patients with suspected coronary artery disease

OBJECTIVES

This study sought to evaluate the interrelation of atherosclerotic burden, as assessed by coronary artery calcium (CAC) score and coronary vascular function, as assessed by quantitative estimates of coronary flow reserve (CFR), with respect to prediction of clinical outcomes.

BACKGROUND

The contribution of coronary vascular dysfunction, atherosclerotic burden, and the 2 combined to cardiac events is unknown.

METHOD

A total of 901 consecutive patients underwent (82)Rubidium myocardial perfusion imaging (MPI) positron emission tomography (PET) and CAC scan. All patients had normal MPI. The primary endpoint was a composite of major adverse cardiac events (MACE) including cardiac death, nonfatal myocardial infarction, late revascularization, and admission for heart failure.

RESULTS

At baseline, CFR decreased (2.15 ± 0.72, 2.02 ± 0.65, and 1.88 ± 0.64, p < 0.0001) with increasing levels of CAC (0, 1 to 399, and ≥400). Over a median of 1.53 years (interquartile range: 0.77 to 2.44), there were 57 MACE. Annual risk-adjusted MACE rates were higher for patients with CFR <2.0 compared with ≥2.0 (1.9 vs. 5.5%/year, p = 0.0007) but were only borderline associated with CAC (3.1%, 3.4%, and 6.2%/year for CAC of 0, 1 to 399, and ≥400, respectively; p = 0.09). Annualized adjusted MACE was increased in the presence of impaired CFR even among patients with CAC = 0 (1.4% vs. 5.2%, p = 0.03). Cox proportional hazards analysis revealed that CFR improved model fit, risk discrimination, and risk reclassification over clinical risk, whereas CAC only modestly improved model fit without improving risk discrimination or reclassification.

CONCLUSIONS

In symptomatic patients with normal MPI, global CFR but not CAC provides significant incremental risk stratification over clinical risk score for prediction of major adverse cardiac events.

Quantitative cardiac positron emission tomography: the time is coming!

In the last 20 years, the use of positron emission tomography (PET) has grown dramatically because of its oncological applications, and PET facilities are now easily accessible. At the same time, various groups have explored the specific advantages of PET in heart disease and demonstrated the major diagnostic and prognostic role of quantitation in cardiac PET. Nowadays, different approaches for the measurement of myocardial blood flow (MBF) have been developed and implemented in user-friendly programs. There is large evidence that MBF at rest and under stress together with the calculation of coronary flow reserve are able to improve the detection and prognostication of coronary artery disease. Moreover, quantitative PET makes possible to assess the presence of microvascular dysfunction, which is involved in various cardiac diseases, including the early stages of coronary atherosclerosis, hypertrophic and dilated cardiomyopathy, and hypertensive heart disease. Therefore, it is probably time to consider the routine use of quantitative cardiac PET and to work for defining its place in the clinical scenario of modern cardiology.

Matching between regional coronary vasodilator capacity and corresponding circumferential strain in individuals with normal and increasing body weight

BACKGROUND

To define the relationship between regional coronary vasodilator capacity and myocardial circumferential strain at rest in normal weight, overweight, and obese individuals with normal global left-ventricular function.

METHODS AND RESULTS

Myocardial blood flow at rest and during pharmacologic vasodilation was measured with (13)N-ammonia PET/CT in mL/g/minute in normal weight control (CON, n = 12), overweight (OW, n = 10), and obese individuals (OB, n = 10). In addition, resting myocardial function was evaluated as circumferential strain (Єc, %) by MRI. Global myocardial flow reserve (MFR) did not differ significantly between CON and OW (2.98 ± 0.96 vs 2.70 ± 0.66, P = .290), whereas it declined significantly in OB (1.98 ± 1.04, P = .030). Further, global Єc (%) was comparable between CON, OW, and OB (-0.24 ± 0.03, -0.23 ± 0.02, and -0.23 ± 0.04) but it was lowest in OB when normalized to the rate-pressure product (NЄc: -0.31 ± 0.06, -0.32 ± 0.05, and -0.26 ± 0.08). When MFR of the three major coronary territories was correlated with corresponding Єc, a positive association was observed in CON (r = 0.36, P = .030), in OW (r = 0.54, P = .002), and also in OB when relating NЄc to coronary vascular resistance during pharmacologic vasodilation (r = -0.46, P = .010).

CONCLUSIONS

Higher coronary vasodilator capacity is related to corresponding regional circumferential strain at rest in non-obese individuals, while this is also observed for reduced MFR in obesity.

Assessment of coronary heart disease by CT angiography: current and evolving applications

Computed tomography angiography (CTA) of the heart is a rapidly evolving application for comprehensive assessment of coronary arterial anatomy, myocardial function, perfusion, and myocardial viability. Thus, cardiac CTA is capable of retrieving the most critical information for guiding the management of patients with suspected coronary heart disease (CHD). Ongoing technologic advancements have allowed acquiring such information within minutes, at radiation doses that are lower than those from conventional computed tomography imaging or common nuclear imaging techniques. Cardiac CTA has positioned itself as an imaging modality that may be well suited to fulfill central needs of cardiovascular medicine. This article reviews the evidence for the clinical utility of cardiac CTA in patients with suspected CHD.