Development and evolution of nuclear cardiology and cardiac PET in Canada.

Gated radionuclide angiography and myocardial perfusion imaging were developed in the United States and Europe in the 1970's and soon adopted in Canadian centers. Much of the early development of nuclear cardiology in Canada was in Toronto, Ontario and was quickly followed by new programs across the country. Clinical research in Canada contributed to the further development of nuclear cardiology and cardiac PET. The Canadian Nuclear Cardiology Society (CNCS) was formed in 1995 and became the Canadian Society of Cardiovascular Nuclear and CT Imaging (CNCT) in 2014. The CNCS had a major role in education and advocacy for cardiovascular nuclear medicine testing. The CNCS established the Dr Robert Burns Lecture and CNCT named the Canadian Society of Cardiovascular Nuclear and CT Imaging Annual Achievement Award for Dr Michael Freeman in memoriam of these two outstanding Canadian leaders in nuclear cardiology. The future of nuclear cardiology in Canada is exciting with the expanding use of SPECT imaging to include Tc-99m-pyrophosphate for diagnosis of transthyretin cardiac amyloidosis and the ongoing introduction of cardiac PET imaging.

Outcomes of Pregnancy in Women With Bioprosthetic Heart Valves With or Without Valve Dysfunction.

BACKGROUND: Although pregnancy outcomes in women with normally functioning bioprosthetic valves (BPVs) are often good, structural valve dysfunction (SVD) may adversely affect pregnancy outcomes, but this has not been studied. OBJECTIVES: The aim of this study was to examine outcomes in pregnant women with BPVs and the association with SVD. METHODS: Pregnancy outcomes in women with BPVs were prospectively collected. Adverse maternal cardiac events (CEs) included cardiac death or arrest, sustained arrhythmia, heart failure, thromboembolism, and stroke. Adverse fetal events were also studied. Determinants of adverse events were examined using logistic regression. RESULTS: Overall, 125 pregnancies in women with BPVs were included, 27% with left-sided and 73% with right-sided BPV. SVD was present in 27% of the pregnancies (44% with left-sided BPVs vs 21% with right-sided BPVs; P = 0.009). CEs occurred in 13% of pregnancies and were more frequent in women with SVD compared with those with normally functioning BPVs (26% vs 8%; P = 0.005). CEs were more common in women with left-sided BPVs with SVD vs normally functioning BPVs (47% vs 5%; P = 0.01) but not in women with right-sided BPVs (11% in those with SVD vs 8% in those without SVD; P = 0.67). Left-sided SVD (P = 0.007), maternal age >35 years (P = 0.001), and a composite variable of "high-risk" features (P = 0.006) were predictors of CEs. Fetal events occurred in 28% of pregnancies. CONCLUSIONS: In this cohort of young women with BPVs, SVD was present in 27% at the first antenatal visit and negatively affected pregnancy outcomes. In particular, SVD of left-sided BPVs was associated with high rates of adverse outcomes.

Tricuspid Intervention Following Pulmonary Valve Replacement in Adults With Congenital Heart Disease.

BACKGROUND: Tricuspid regurgitation (TR) is common among adults with corrected tetralogy of Fallot (TOF) or pulmonary stenosis (PS) referred for pulmonary valve replacement (PVR). Yet, combined valve surgery remains controversial. OBJECTIVES: This study sought to evaluate the impact of concomitant tricuspid valve intervention (TVI) on post-operative TR, length of hospital stay, and on a composite endpoint consisting of 7 early adverse events (death, reintervention, cardiac electronic device implantation, infection, thromboembolic event, hemodialysis, and readmission). METHODS: The national Canadian cohort enrolled 542 patients with TOF or PS and mild to severe TR who underwent isolated PVR (66.8%) or PVR+TVI (33.2%). Outcomes were abstracted from charts and compared between groups using multivariable logistic and negative binomial regression. RESULTS: Median age at reintervention was 35.3 years. Regardless of surgery type, TR decreased by at least 1 echocardiographic grade in 35.4%, 66.9%, and 92.8% of patients with pre-operative mild, moderate, and severe insufficiency. In multivariable analyses, PVR+TVI was associated with an additional 2.3-fold reduction in TR grade (odds ratio [OR]: 0.44; 95% confidence interval [CI]: 0.25 to 0.77) without an increase in early adverse events (OR: 0.85; 95% CI: 0.46 to 1.57) or hospitalization time (incidence rate ratio: 1.17; 95% CI: 0.93 to 1.46). Pre-operative TR severity and presence of transvalvular leads independently predicted post-operative TR. In contrast, early adverse events were strongly associated with atrial tachyarrhythmia, extracardiac arteriopathy, and a high body mass index. CONCLUSIONS: In patients with TOF or PS and significant TR, concomitant TVI is safe and results in better early tricuspid valve competence than isolated PVR.

Stress Echocardiographic Evaluation for D-Transposition of the Great Arteries after Atrial Redirection: Unmasking Early Signs of Myocardial Dysfunction and Baffle Stenosis.

BACKGROUND: The authors used semisupine cycle ergometry stress echocardiography to assess cardiac function and unmask baffle stenosis in patients with d-transposition of the great arteries after atrial redirection surgery. METHODS: This was a retrospective review of semisupine cycle ergometry stress echocardiography performed in 53 patients (64% male; mean age, 24.0 years; 90% Mustard procedure) and 56 healthy control subjects. Incremental exercise to volitional fatigue was performed. Hemodynamic data, echocardiographic cardiac dimensions, area change, tissue Doppler velocities, strain, ventricular synchronization, and superior vena cava flow velocities before and immediately after exercise are reported. RESULTS: Patients had lower exercise capacity (870 vs 1,854 J/kg, P < .001) and peak heart rates (132 vs 167 beats/min, P < .001). Stroke volume index did not increase with exercise (45 vs 47 mL/m2, P = .400). Cardiac index increased in both groups with exercise (3.0 vs 6.1 and 2.9 vs 7.0 L/min/m2, P < .001) and was higher in control subjects (P = .006). Right ventricular diastolic and systolic areas decreased significantly with exercise in both the short-axis and four-chamber views. Right and left ventricular contraction time shortened with exercise (405 vs 247 and 338 vs 217 msec, P < .001) and remained synchronous (ratio of right ventricular to left ventricular contraction time = 0.080). Doppler velocities in patients with baffle obstruction were higher in the lower superior vena cava with exercise compared with nonobstructed patients (1.87 vs 1.46 m/sec, P = .020) and normalized after catheter intervention (1.49 vs 1.46 m/sec, P = .800). CONCLUSIONS: Patients with d-transposition of the great arteries have lower exercise capacity and peak heart rates. The systemic right ventricle presents a lesser but qualitatively normal systolic response and decreased diastolic filling. Semisupine cycle ergometry stress echocardiography unmasked SVC obstruction.

Sequential Right and Left Ventricular Assessment in Posttetralogy of Fallot Patients with Significant Pulmonary Regurgitation.

BACKGROUND: The natural history of right ventricular (RV) and left ventricular (LV) size and function among adults with tetralogy of Fallot (TOF) repair and hemodynamically significant pulmonary regurgitation (PR) is not known. The main aim of this study was to determine changes in RV and LV size and function over time in an adult population with TOF repair and hemodynamically significant pulmonary regurgitation. METHODS: Forty patients with repaired TOF and hemodynamically significant PR were included. These patients were identified on the basis of having more than one CMR between January 2008 and 2015. Patients with a prosthetic pulmonary valve or any cardiac intervention between CMR studies were excluded. Rate of progression (ROP) of RV dilation was determined for both indexed right ventricular end-systolic volume (RVESVi) and indexed right ventricular end-diastolic volume (RVEDVi), and calculated as the difference between the last and first volumes divided by the number of years between CMR#1 and CMR#2. Subjects were also divided into two groups based on the distribution of the ROP of RV dilation: Group I-rapid ROP (>50th percentile) and Group II-slower ROP (≤50th percentile). RESULTS: The interval between CMR#1 and CMR#2 was 3.9 ± 1.7 years (range 1-8 years). We did find a significant change in RVEDVi and RVESVi over this time period, although the magnitude of change was small. Nine patients (23%) had a reduction in right ventricular ejection fraction (RVEF) by greater than 5%, 13 patients (33%) had an increase in RVEDVi by greater than 10 mL/m2 and seven patients (18%) had an increase in RVESVi by greater than 10 mL/m2 . Median ROP for RVEDVi was 1.8 (range -10.4 to 21.8) mL/(m2 year); RVESVi 1.1 (range -5.8 to 24.5) mL/(m2 year) and RVEF -0.5 (range -8 to 4)%/year. Patients with a rapid ROP had significantly larger RV volumes at the time of CMR#1 and lower RVEF as compared to the slow ROP group. There was no overall significant change in LVEDVi, LVESVi, or LVEF over this time period. CONCLUSIONS: We have demonstrated, in a small population of patients with hemodynamically significant PR, that there is a small increase in RV volumes and decrease in RVEF over a mean 4-year period. We believe it to be reasonable practice to perform CMR at least every 4 years in asymptomatic patients with repaired TOF and hemodynamically significant PR. We found that LV volumes and function remained stable during the study period, suggesting that significant progressive LV changes are less likely to occur over a shorter time period. Our results inform a safe standardized approach to monitoring adults with hemodynamically significant PR post TOF repair and assist in planning allocation of this expensive and limited resource.

Assessing the need for nuclear cardiology and other advanced cardiac imaging modalities in the developing world.

BACKGROUND: In 2005, 80% of cardiovascular disease (CVD) deaths occurred in low- to middle-income countries (i.e., developing nations). Cardiovascular imaging, such as myocardial perfusion SPECT, is one method that may be applied to detect and foster improved detection of at-risk patients. This document will review the availability and utilization for nuclear cardiology procedures worldwide and propose strategies to devise regional centers of excellence to achieve quality imaging around the world. METHODS: As a means to establish the current state of nuclear cardiology, International Atomic Energy Agency member and non-member states were queried as to annual utilization of nuclear cardiology procedures. Other sources for imaging statistics included data from medical societies (American Society of Nuclear Cardiology, European Society of Cardiology, and the European Association of Nuclear Medicine) and nuclear cardiology working groups within several nations. Utilization was calculated by dividing annual procedural volume by 2007 population statistics (/100,000) and categorized as high (>1,000/100,000), moderate-high (250-999/100,000), moderate (100-249/100,000), low-moderate (50-99/100,000) and low (<50/100,000). RESULTS: High nuclear cardiology utilization was reported in the United States, Canada, and Israel. Most Western European countries, Australia, and Japan reported moderate-high utilization. With the exception of Argentina, Brazil, Colombia and Uruguay, South America had low usage. This was also noted across Eastern Europe, Russia, and Asia. Utilization patterns generally mirrored each country's gross domestic product. However, nuclear cardiology utilization was higher for developing countries neighboring moderate-high "user" countries (e.g., Algeria and Egypt); perhaps the result of accessible high-quality training programs. CONCLUSIONS: Worldwide utilization patterns for nuclear cardiology vary substantially and may be influenced by physician access to training and education programs. Development of regional training centers of excellence can guide utilization of nuclear cardiology through the application of guideline- and appropriateness-driven testing, training, continuing education, and quality assurance programs aiding developing nations to confront the epidemics of CVD.