Exercise capacity as a predictor of coronary microvascular dysfunction

Introduction

Exercise capacity (EC) is an important prognostic test in patients with coronary artery disease (CAD). Positron-emission tomography (PET) is an important risk-stratifying tool to tailor management of patients with coronary artery disease.

Purpose

We aimed to assess EC in predicting positron emission tomography (PET) myocardial perfusion imaging (MPI) derived coronary flow reserve (CFR).

Methods

Consecutive patients who had clinically indicated PET MPI and EC were included. EC was defined based on peak metabolic equivalents (METS) achieved during exercise stress test. Myocardial blood flow (MBF) in ml/gm/min was obtained from dynamic PET MPI images at rest and peak hyperemia. The coronary flow reserve (CFR) was calculated as the ratio of stress to rest MBF of the left ventricle.

Results

The study population consisted of 511 patients who underwent PET MPI and EC testing (mean age 56 (±11), 71% male). Cardiovascular risk factors were prevalent (75% hypertensive, 82% dyslipidemic, 43% diabetics, 27% known CAD). Peak METS >6 was achieved in 81% of patients, and the CFR <2 was present in 27%. In multivariable logistic regression models adjusted for age, sex, cardiovascular risk factors (hypertension, diabetes, dyslipidemia) and medication use (angiotensin converting enzyme inhibitor/angiotensin receptor blocker, statins, beta-blockers), patients with peak METS >6 had a statistically significant lower odds of microvascular dysfunction (CFR <2: OR 0.43, 95% CI 0.26–0.71, p=0.001). Assessment of discrimination showed the model with CFR <2 had an incremental improvement of Harrell's C statistic over clinical variables (0.65 vs 0.69, p=0.02).

Conclusion

Our findings showed exercise capacity was a good predictor of CFR and microvascular coronary health over and above clinical variables. Further studies are needed to assess the prognostic interplay between EC and CFR.

Funding Acknowledgement

Type of funding sources: None.

Prognostic value of coronary flow reserve and coronary calcification in patients with suspected coronary artery disease

Introduction

Current cardiac PET and computed tomography imaging allows the simultaneous acquisition of anatomic and physiological data for patients suspected of CAD.

Purpose

We aimed to evaluate the incremental prognostic value of coronary artery calcium (CAC) score and coronary flow reserve (CFR) in patients with suspected coronary artery disease (CAD) undergoing positron emission tomography (PET) myocardial perfusion imaging (MPI).

Methods

We included consecutive patients who underwent PET MPI and CAC score calculation at Houston Methodist Hospital between August 2019 and January 2022. MPI and CAC scores were obtained in the same setting. The primary endpoint of the study was MACE. Cox proportional hazard regression was used to assess the incremental prognostic value of CAC and CFR by sequentially adding the variables to a model that included clinical and PET variables.

Results

A total of 2,072 patients (mean age 65.7±11.6 years, 54.7% women) were included in the analysis. Risk factors were prevalent (86.1% hypertension, 75.2% dyslipidemia, 45.5% diabetes). In total, 25.3% of the cohort had a CAC score of 0, 38.1% had CAC ≥400, and 39.9% had CFR <2. Over a median follow up of 6.26 (IQR 1.7–12.4) months, 66 (3.2%) patients had cardiac death/nonfatal myocardial infarction. CFR score added incremental prognostic value over clinical and perfusion variables alone (base model: c-index 0.75; Akaike information criterion [AIC]: 1,860.6; p<0.001; CFR model: c-index 0.78; AIC: 1,842.4; p=0.041). However, CAC score did not show an increased prognostic utility (CAC model: c-index 0.76; AIC: 1,854.8; p=0.087 vs. base model), and neither did the combined model of CAC and CFR scores (c-index 0.79; AIC: 1,839.4; p=0.366 vs. CFR model).

Conclusions

Among patients referred for PET MPI, CFR score added an increased prognostic value over clinical and MPI variables. However, when evaluating the prognostic utility of CAC alone, or of CAC and CFR combined, the multivariable model did not show any increased prognostic potential.

Funding Acknowledgement

Type of funding sources: None.

Incremental prognostic value of coronary flow reserve derived from SPIM digital positron emission tomography

Introduction

Positron emission tomography (PET) myocardial perfusion imaging (MPI) is an established test in the diagnosis and prognosis of patients with cardiac diseases. Silicon photomultiplier (SiPM) digital PET is the latest advancement in this technology with improved detector sensitivity, coincidence time resolution, and spatial resolution, allowing for Sub-milliSievert cardiac PET MPI.

Purpose

We aimed to assess the independent and incremental prognostic value of SiPM digital PET derived coronary flow reserve (CFR) to clinical and nuclear variables.

Methods

Consecutive patients who had clinically indicated digital Rubidium PET MPI were included. Rubidium dose was 10–20 mCi according to patient's weight. Patients were followed from the date of imaging to incident major adverse cardiovascular event (MACE: inclusive of all-cause death, myocardial infarction, admission for heart failure and late revascularization – percutaneous coronary intervention (PCI) or coronary artery bypass graft (CABG) >90 days after imaging).

Results

The study population consisted of 2,893 patients with clinically indicated PET MPI (mean age 67 (±12), 53% male, 41% Caucasian). Cardiovascular risk factors were prevalent (88% hypertensive, 80% dyslipidemic, 47% diabetics, 18% ever smoking). After a mean follow-up of 8±7 months, 250 patients (8.6%, 10.7 per 1000 person-year) experienced MACE (90 D / 38 MI / 51 PCI / 11 CABG / 113 HF). In nested multivariable cox models, CFR was independently associated with incident MACE (HR 0.38, 95% CI 0.29–0.51, p<0.001) and incrementally improved risk prediction (Harrell's C=0.77, p=0.002).

Conclusion

Our findings showed that a Sub-milliSievert SiPM digital PET-derived CFR provided incremental value in risk-stratifying patients and identifying those at increased risk of incident outcomes.

Funding Acknowledgement

Type of funding sources: None.

Left ventricular volumes on positron emission tomography: validation against cardiovascular magnetic resonance

Introduction

Cardiovascular magnetic resonance (CMR) is the gold standard for determination of left ventricular volumes (LVV), including end diastolic volume (LVEDV) and end systolic volume (LVESV). With incorporation of ECG gating, the quantitative analysis of ventricular function can be achieved in Positron Emission Tomography (PET) studies. However, the accuracy of LVV quantification using PET has not been shown in previous studies.

Purpose

We aimed to assess the inter-study variability of LVEDV and LVESV between CMR and PET.

Methods

Consecutive patients who underwent both PET and CMR within 1 year were identified from prospective institutional registries. LVV on PET was compared against CMR as a reference standard using several statistical measures of agreement.

Results

The study population consisted of 233 patients (mean age 60.8±13.6 years, 64.8% male). The median (IQR) duration between CMR and PET was 41 (11–96) days. The median (IQR) LVEDV values were 144 (107–196) on PET and 178 (138–236) on CMR (mean difference 36.09±2.36, p<0.001). As shown in Figure 1, there was a good correlation (Spearman rho=0.88, p<0.001; Intraclass Correlation Coefficient 0.88, 95% CI 0.84–0.90, P<0.001) with moderate limits of agreement (95% limits of agreement −108.17–35.99). A total of 0% and 3.9% of the cohort had LVEDV >150 ml/m2 by CMR and PET respectively. Overall results were similar with LVESV values and similar in subgroup analysis of patients with a low EF (<40%), a coronary artery disease scar, LV hypertrophy and of patients with defibrillators.

Conclusion

Our analysis has shown a good correlation of LVV between PET and CMR, indicating PET derived LVV can accurately be used in the diagnosis and management of patients.

Funding Acknowledgement

Type of funding sources: None.

Prognostic value of PET derived coronary flow reserve: should we correct for resting perfusion product?

Introduction

Positron emission tomography (PET) myocardial perfusion imaging (MPI) derived coronary flow reserve (CFR) is an important risk-stratifying tool to tailor management of patients with coronary artery disease. Resting myocardial blood flow (MBF) is positively correlated to the product of resting heart rate and systolic blood product (resting pressure product – RPP), and can in turn lead to lower CFR in the setting of normal stress MBF.

Purpose

We aimed to assess the comparative incremental prognostic value of uncorrected to RPP-corrected CFR in predicting incident events.

Methods

Consecutive patients who had clinically indicated PET MPI were included. Patients were followed from the date of imaging to incident major adverse cardiovascular event (MACE: inclusive of all-cause death, myocardial infarction, admission for heart failure and late revascularization – percutaneous coronary intervention (PCI) or coronary artery bypass graft (CABG) >90 days after imaging).

Results

The study population consisted of 2,893 patients with clinically indicated PET MPI (mean age 67 (±12), 53% male, 41% Caucasian). Cardiovascular risk factors were prevalent (88% hypertensive, 80% dyslipidemic, 47% diabetics, 18% ever smoking). After a mean follow-up of 8±7 months, 250 patients (8.6%, 10.7 per 1000 person-year) experienced MACE (90 D/38 MI/51 PCI/11 CABG/113 HF). Both uncorrected and corrected CFR were independently associated with incident MACE (HR 0.38, 95% CI 0.29–0.51, p<0.001 and 0.61, 95% CI 0.50–0.76, p<0.001 respectively). A comparison of model incremental prognostic value showed the model with uncorrected CFR had a statistically higher Harrell's C (0.76 vs 0.77, p=0.23).

Conclusion

Our findings showed that the prognostic value of CFR was preserved even in the setting of high resting blood pressure or heart rate. This suggests that correction for RPP should be selective.

Funding Acknowledgement

Type of funding sources: None.

Coronary microvascular health in patients with prior COVID-19 infection and no known CAD

Introduction

Although most patients recovering from acute COVID-19 infection have complete resolution of symptoms, some have cardiopulmonary symptoms lingering long after the acute phase of the disease. One proposed mechanism involves chronicity of COVID-19 associated with myocarditis and endotheliopathy.

Purpose

To determine the coronary microvascular health of patients with prior COVID-19 and no known coronary artery disease (CAD) using positron emission tomography (PET).

Methods

Cases consisting of patients without known CAD but previous COVID-19 infection who had clinically indicated PET imaging were matched 1:4 on clinical and cardiovascular risk factors to controls having no prior COVID-19 infection. Myocardial blood flow (MBF) in ml/gm/min was obtained from dynamic images at rest and peak hyperemia. The coronary flow reserve (CFR) was calculated as the ratio of stress to rest MBF of the left ventricle. Coronary microvascular dysfunction (CMD) was defined as CFR<2.

Results

The study population consisted of 315 patients, 25% (n=80) of which had prior COVID-19 infection (mean±SD age 64±11 years, 46% men). The median (IQR) number of days between COVID-19 infection and PET imaging was 190 (85–268) days. After adjusting for age, gender and cardiovascular risk factors, patients with prior COVID-19 and no known CAD had a statistically significant higher odds of having a CFR <2 (OR 4.9, 95% CI 2.3–10.1 p<0.001) and CFR <2 normalized to patient's rate-systolic blood pressure product (OR 2.8, 95% CI 1.6–5.0 p=0.001). The annualized event rate for the composite outcome of all-cause death, myocardial infarction, admission for heart failure exacerbation and late revascularization was higher in cases vs controls and in those with CMD.

Conclusion

Our analysis showed that patients with prior COVID-19 and no known CAD had higher rates of CMD, and that the presence of CMD was associated with higher risk of incident cardiovascular events.

Funding Acknowledgement

Type of funding sources: None.

Comparative prognostic utility of visual grade and heart-to-contralateral lung ratio in patients undergoing 99mTc-pyrophosphate radiotracer cardiac scintigraphy

Introduction

Transthyretin (ATTR) cardiac amyloidosis (CA) is an underdiagnosed form of restrictive cardiomyopathy leading to a rapid progression into heart failure. 99mTc-labeled radiotracer cardiac scintigraphy is crucial for the evaluation of CA. Semiquantitative (Perugini visual grade) and quantitative (heart-to-contralateral lung ratio, H/CL) parameters are used to assessing CA via cardiac scintigraphy.

Purpose

We aimed to assess the comparative prognostic utility of the Perugini visual grade and heart to contralateral lung ratio.

Methods

The study population was identified based on an institutional registry of consecutive patients undergoing 99mTc-PYP radiotracer cardiac scintigraphy for suspected CA between January 2020-October 2021. The H/CL is calculated by the fraction of heart region of interest (ROI) mean uptake counts to the contralateral chest ROI. The visual scoring system compares uptake between bone (rib) and heart where 0 = absent cardiac uptake, 1 = uptake less than bone, 2 = uptake equal to bone, and 3 = is uptake greater than bone. Ejection fraction (EF) was obtained from echocardiographic studies done around the time of cardiac scintigraphy. MACE was defined as a composite of inclusive of all-cause death, myocardial infarction, admission for heart failure and late revascularization – percutaneous coronary intervention (PCI) or coronary artery bypass graft (CABG) >90 days after imaging.

Results

A total of 330 patients (mean age 70.9±12.2 years, 62.2% male) were included in the analysis. Risk factors were prevalent (59.7% hypertension, Heart Failure 68.3%, 26.5% dyslipidemia, 26.2% diabetes) (Table 1). In total, 32.6% of the cohort had studies suggestive of ATTR CA. Median time between echocardiography and cardiac scintigraphy was 7 days (IQR 5–42 days). A higher frequency of MACE was reported in patients with a 2+ visual grade (30% vs 42%, p=0.03). A H/CL >1.5 was associated with borderline significance (43% vs 35% p=0.07).

Conclusion

Our analysis showed that the Perugini visual grading of transthyretin cardiac amyloidosis conferred the best prognostic utility contrary to heart to contralateral lung ratio in 99mTc-PYP radiotracer cardiac scintigraphy.

Funding Acknowledgement

Type of funding sources: None.

Outcome of sedentary patients: does the power of zero cac make a difference?

Introduction

Coronary artery calcium score (CACS) and exercise capacity (EC) are both independent prognostic tests in coronary artery disease (CAD).

Purpose

We aimed to assess the incremental prognostic role of EC to CACS, particularly in those with absent or low coronary calcification.

Methods

The cohort consisted of patients who had clinically indicated exercise stress testing and CACS assessment with a median of 27 days of each other. EC was defined based on peak metabolic equivalents (METS) achieved during exercise stress test. CACS was determined using the Agatston method. Patients were followed from the latest test date to incident MACE (inclusive of all-cause death, non-fatal myocardial infarction, late revascularization and admission for heart failure).

Results

There were a total of 1932 patients in the study population (mean age 56±12, 42% female, 48% hypertension, 21% diabetes, 48% dyslipidemia). Peak METS <6 was achieved in 8% of patients, and the median (IQR) CACS was 9 (0–203). Patients with EC <6 METS had doubling of their event rate across strata of CACS, even amongst patients with absent or low coronary calcifications (CACS 0: 4.6 vs 10.9; CACS 1–99: 10.4 vs 20.4; MACE per 1000 person year in patients with peak METS ≥ vs <6 respectively) (Figure 1).

Conclusion

Our findings showed that poor exercise capacity was associated with higher risk even in patients with absent or low coronary calcification.

Funding Acknowledgement

Type of funding sources: None.