Anatomic distribution of myocardial ischemia as a determinant of exercise-induced ST-segment depression

Impact of Mitral Regurgitation Severity and Cause on Effort Tolerance-Integrated Stress Myocardial Perfusion Imaging and Echocardiographic Assessment of Patients With Known or Suspected Coronary Artery Disease Undergoing Exercise Treadmill Testing

Background Mitral regurgitation ( MR ) has the potential to impede exercise capacity; it is uncertain whether this is because of regurgitation itself or the underlying cause of valvular insufficiency. Methods and Results The population comprised 3267 patients who underwent exercise treadmill myocardial perfusion imaging and transthoracic echocardiography within 6±8 days. MR was present in 28%, including 176 patients (5%) with moderate or greater MR . Left ventricular systolic function significantly decreased and chamber size increased in relation to MR , paralleling increments in stress and rest myocardial perfusion deficits (all P<0.001). Exercise tolerance (metabolic equivalents of task) decreased stepwise in relation to graded MR severity ( P<0.05). Workload was significantly lower with mild versus no MR (mean±SD, 9.8±3.0 versus 10.1±3.0; P=0.02); magnitude of workload reduction significantly increased among patients with advanced versus those with mild MR (mean±SD, 8.6±3.0 versus 9.8±3.0; P<0.001). MR -associated exercise impairment was accompanied by lower heart rate and blood pressure augmentation and greater dyspnea (all P<0.05). Both functional and nonfunctional MR subgroups demonstrated significantly decreased effort tolerance in relation to MR severity ( P≤0.01); impairment was greater with functional MR ( P=0.04) corresponding to more advanced left ventricular dysfunction and dilation (both P<0.001). Functional MR predicted reduced metabolic equivalent of task-based effort (B=-0.39 [95% CI, -0.62 to -0.17]; P=0.001) independent of MR severity. Among the overall cohort, advanced (moderate or greater) MR was associated with reduced effort tolerance (B=-1.36 [95% CI, -1.80 to -0.93]; P<0.001) and remained significant ( P=0.01) after controlling for age, clinical indexes, stress perfusion defects, and left ventricular dysfunction. Conclusions MR impairs exercise tolerance independent of left ventricular ischemia, dysfunction, and clinical indexes. Magnitude of exercise impairment parallels severity of MR .

Right Ventricular Dysfunction Impairs Effort Tolerance Independent of Left Ventricular Function Among Patients Undergoing Exercise Stress Myocardial Perfusion Imaging

BACKGROUND

Right ventricular (RV) and left ventricular (LV) function are closely linked due to a variety of factors, including common coronary blood supply. Altered LV perfusion holds the potential to affect the RV, but links between LV ischemia and RV performance, and independent impact of RV dysfunction on effort tolerance, are unknown.

METHODS AND RESULTS

The population comprised 2051 patients who underwent exercise stress myocardial perfusion imaging and echo (5.5±7.9 days), among whom 6% had echo-evidenced RV dysfunction. Global summed stress scores were ≈3-fold higher among patients with RV dysfunction, attributable to increments in inducible and fixed LV perfusion defects (all P≤0.001). Regional inferior and lateral wall ischemia was greater among patients with RV dysfunction (both P<0.01), without difference in corresponding anterior defects (P=0.13). In multivariable analysis, inducible inferior and lateral wall perfusion defects increased the likelihood of RV dysfunction (both P<0.05) independent of LV function, fixed perfusion defects, and pulmonary artery pressure. Patients with RV dysfunction demonstrated lesser effort tolerance whether measured by exercise duration (6.7±2.8 versus 7.9±2.9 minutes; P<0.001) or peak treadmill stage (2.6±0.9 versus 3.1±1.0; P<0.001), paralleling results among patients with LV dysfunction (7.0±2.9 versus 8.0±2.9; P<0.001|2.7±1.0 versus 3.1±1.0; P<0.001 respectively). Exercise time decreased stepwise in relation to both RV and LV dysfunction (P<0.001) and was associated with each parameter independent of age or medication regimen.

CONCLUSIONS

Among patients with known or suspected coronary artery disease, regional LV ischemia involving the inferior and lateral walls confers increased likelihood of RV dysfunction. RV dysfunction impairs exercise tolerance independent of LV dysfunction.

Myocardial perfusion pattern for stratification of ischemic mitral regurgitation response to percutaneous coronary intervention

OBJECTIVE

Ischemic mitral regurgitation (MR) is common, but its response to percutaneous coronary intervention (PCI) is poorly understood. This study tested the utility of myocardial perfusion imaging (MPI) for the stratification of MR response to PCI.

METHODS

MPI and transthoracic echocardiography (echo) were performed among patients undergoing PCI. MPI was used to assess stress/rest myocardial perfusion. MR was assessed via echo (performed before and after PCI).

RESULTS

A total of 317 patients with abnormal myocardial perfusion on MPI underwent echo 25±39 days before PCI. MR was present in 52%, among whom 24% had advanced (≥moderate) MR. MR was found to be associated with left ventricular (LV) chamber dilation on MPI and echo (both P<0.001). The magnitude of global LV perfusion deficits increased in relation to MR severity (P<0.01). Perfusion differences were greatest for global summed rest scores, which were 1.6-fold higher among patients with advanced MR versus those with mild MR (P=0.004), and 2.4-fold higher versus those without MR (P<0.001). In multivariate analysis, advanced MR was found to be associated with a fixed perfusion defect size on MPI [odds ratio 1.16 per segment (confidence interval 1.002-1.34), P=0.046], independent of LV volume [odds ratio 1.10 per 10 ml (confidence interval 1.04-1.17), P=0.002]. Follow-up via echo (1.0±0.6 years) demonstrated MR to decrease (≥1 grade) in 31% of patients and increase in 12% of patients. Patients with increased MR after PCI had more severe inferior perfusion defects on baseline MPI (P=0.028), whereas defects in other distributions and LV volumes were similar (P=NS).

CONCLUSION

The extent and distribution of single-photon emission computed tomography-evidenced myocardial perfusion defects impact MR response to revascularization. An increased magnitude of inferior fixed perfusion defects predicts post-PCI progression of MR.

Effect of myocardial perfusion pattern on frequency and severity of mitral regurgitation in patients with known or suspected coronary artery disease

Mitral regurgitation (MR) is common with coronary artery disease as altered myocardial substrate can affect valve performance. Single-photon emission computed tomography myocardial perfusion imaging (MPI) enables assessment of myocardial perfusion alterations. This study examined perfusion pattern in relation to MR. A total of 2,377 consecutive patients with known or suspected coronary artery disease underwent stress MPI and echocardiography within 1.6 ± 2.3 days. MR was present on echocardiography in 34% of patients, among whom 13% had advanced (moderate or more) MR. MR prevalence was higher in patients with abnormal MPI (44% vs 29%, p <0.001), corresponding to increased global ischemia (p <0.001). Regional perfusion varied in left ventricular segments adjacent to each papillary muscle: adjacent to the anterolateral papillary muscle, magnitude of baseline and stress-induced anterior/anterolateral perfusion abnormalities was greater in patients with MR (both p <0.001). Adjacent to the posteromedial papillary muscle, baseline inferior/inferolateral perfusion abnormalities were greater with MR (p <0.001), whereas stress inducibility was similar (p = 0.39). In multivariate analysis, stress-induced anterior/anterolateral and rest inferior/inferolateral perfusion abnormalities were independently associated with MR (both p <0.05) even after controlling for perfusion in reference segments not adjacent to the papillary muscles. MR severity increased in relation to magnitude of perfusion abnormalities in each territory adjacent to the papillary muscles, as evidenced by greater prevalence of advanced MR in patients with at least moderate anterior/anterolateral stress perfusion abnormalities (10.7% vs 3.6%), with similar results when MR was stratified based on rest inferior/inferolateral perfusion (10.4% vs 3.0%, both p <0.001). In conclusion, findings demonstrate that myocardial perfusion pattern in left ventricular segments adjacent to the papillary muscles influences presence and severity of MR.

Computing ischemic regions in the heart with the bidomain model--first steps towards validation

We investigate whether it is possible to use the bidomain model and body surface potential maps (BSPMs) to compute the size and position of ischemic regions in the human heart. This leads to a severely ill posed inverse problem for a potential equation. We do not use the classical inverse problems of electrocardiography, in which the unknown sources are the epicardial potential distribution or the activation sequence. Instead we employ the bidomain theory to obtain a model that also enables identification of ischemic regions transmurally. This approach makes it possible to distinguish between subendocardial and transmural cases, only using the BSPM data. The main focus is on testing a previously published algorithm on clinical data, and the results are compared with images taken with perfusion scintigraphy. For the four patients involved in this study, the two modalities produce results that are rather similar: The relative differences between the center of mass and the size of the ischemic regions, suggested by the two modalities, are 10.8% ± 4.4% and 7.1% ± 4.6%, respectively. We also present some simulations which indicate that the methodology is robust with respect to uncertainties in important model parameters. However, in contrast to what has been observed in investigations only involving synthetic data, inequality constraints are needed to obtain sound results.

Relation of plaque characteristics defined by coronary computed tomographic angiography to ST-segment depression and impaired functional capacity during exercise treadmill testing in patients suspected of having coronary heart disease

Sixty-four-detector-row coronary computed tomographic angiography (CCTA) has been proposed for the evaluation of low- to intermediate-risk patients with suspected coronary artery disease (CAD). Historically, exercise treadmill testing (ETT) measures of ST-segment depression (STD) and the Duke treadmill score (DTS) have been used to evaluate myocardial ischemia and functional capacity. The relation of plaque characteristics on CCTA to STD and DTS is unknown. In this study, 156 low- to intermediate-risk patients without known CAD who underwent ETT and CCTA were evaluated. By ETT, 22% (n = 35) had STD and 27% (n = 42) had abnormal DTS. On CCTA, 21% (n = 33) had obstructive CAD (>or=70% stenosis) and 49% (n = 77) had nonobstructive CAD (<70% stenosis). Forty-six percent of patients (n = 16) with and 15% (n = 15) without STD had obstructive CAD. After multivariate adjustment, only age and obstructive CAD on CCTA predicted STD (odds ratio [OR] 1.59, 95% confidence interval [CI] 1.08 to 2.34 per decade, and OR 3.38, 95% CI 1.32 to 8.64, respectively) and abnormal DTS (OR 1.61, 95% CI 1.14 to 2.28, and OR 4.67, 95% CI 1.97 to 11.03, respectively). After adjustment for age, more coronary segments with mixed plaque, in contrast to calcified or noncalcified plaque, predicted STD (OR 1.48, 95% CI 1.18 to 1.85) and abnormal DTS (OR 1.30, 95% CI 1.05 to 1.61). In conclusion, measures of plaque on CCTA identify patients more likely to have STD and higher risk DTS, while providing incremental diagnostic yield for the detection of obstructive CAD beyond ETT.

Multidetector computed tomography coronary artery plaque predictors of stress-induced myocardial ischemia by SPECT

BACKGROUND

Atherosclerosis imaging by multidetector computed tomography (MDCT) detects coronary artery plaque extent, distribution, location and composition. In contrast, functional imaging by single-photon emission computed tomography (SPECT) identifies perfusion defects known to predict prognosis of coronary heart disease (CHD). We sought to determine whether anatomic measures of plaque by MDCT predict functional measures of CHD by SPECT and thus, serve as measures of adverse cardiovascular prognosis.

METHODS AND RESULTS

Consecutive low-to-intermediate risk symptomatic patients without known CHD (n=163) underwent both stress SPECT and MDCT. MDCT plaque extent and distribution were graded by a segment stenosis score (summation of luminal obstruction in all coronary segments) and segment involvement score (summation of segments exhibiting any plaque), respectively. Plaque location was assessed with a segments-at-risk score (plaque extent weighted by proximity) and a modified Duke CAD index. Plaque composition was graded as non-calcified, calcified and mixed. SPECT findings--summed stress (SSS), rest (SRS) and difference (SDS) scores--were compared to MDCT plaque scores. In univariate analyses, segment stenosis score (p=0.006), segments-at-risk score (p=0.002), Duke CAD index (p=0.02), and mixed plaque score (p=0.01) predicted severely abnormal SPECT. Highest compared to lowest quartile mixed plaque scores were predictive of higher SSS (8.1+/-10.3 versus 3.5+/-5.7, p<0.001), SRS (3.2+/-7.7 versus 0.9+/-3.1, p=0.008), and SDS (4.9+/-6.4 versus 2.6+/-3.9, p=0.012). In contrast, higher segment involvement scores, calcified and non-calcified plaque scores did not predict higher SPECT measures of ischemia. In multivariable analyses, comparing highest to lowest quartiles, individuals with high segment stenosis scores [odds ratio (OR) 1.97 (1.22-3.39), p=0.008], segments-at-risk scores [OR 1.71 (1.24-2.58), p=0.005], highest risk Duke CAD index category [OR 2.25 (1.12-4.41), p=0.02], and mixed plaque scores [OR 1.64 (1.10-2.43), p=0.01] had more severely abnormal SPECT scans.

CONCLUSIONS

In low-to-intermediate risk patients without known CHD, MDCT coronary artery plaque assessment successfully identify patients at higher risk of increased extent, severity and reversibility of myocardial perfusion defects by SPECT. Anatomic MDCT findings, including plaque extent, location and composition, are independent predictors of functional ischemia and severe CHD by SPECT and thus, represent markers of adverse cardiovascular prognosis prior to the occurrence of clinical cardiovascular events.