Combined assessment of left ventricular perfusion and function by gated single-photon emission computed tomography for the risk stratification of high-risk hypertensive patients

Basal Septal Hypertrophy as the Early Imaging Biomarker for Adaptive Phase of Remodeling Prior to Heart Failure

Hypertension plays a dominant role in the development of left ventricular (LV) remodeling and heart failure, in addition to being the main risk factor for coronary artery disease. In this review, we focus on the focal geometric and functional tissue aspects of the LV septal base, since basal septal hypertrophy (BSH), as the early imaging biomarker of LV remodeling due to hypertensive heart disease, is detected in cross-sectional clinic studies. In addition, the validation of BSH by animal studies using third generation microimaging and relevant clinical observations are also discussed in the report. Finally, an evaluation of both human and animal quantitative imaging studies and the importance of combined cardiac imaging methods and stress-induction in the separation of adaptive and maladaptive phases of the LV remodeling are pointed out. As a result, BSH, as the early imaging biomarker and quantitative follow-up of functional analysis in hypertension, could possibly contribute to early treatment in a timely fashion in the prevention of hypertensive disease progression to heart failure. A variety of stress stimuli in etiopathogenesis and the difficulty of diagnosing pure hemodynamic overload mediated BSH lead to an absence of the certain prevalence of this particular finding in the population.

Hemodynamic stress and microscopic remodeling

BACKGROUD

Heart responds to physiologic and pathologic conditions and sympathetic drive plays an important role. It has been documented that LV base is more dominantly affected by sympathetic drive compared to the other regions. LV base is more dominantly exposed to wall stress in the initial period of remodeling due to pressure-overload, since LV cavity is the largest at base. Basal septal hypertrophy (BSH) in cross-sectional data is associated with the early phase of hypertensive heart disease. BSH was confirmed by 3rd generation microscopic ultrasound in small animals. BSH as the closest location to increased afterload could be detected in variety of stress stimuli and result in a huge septal hypertrophy in advance cases possibly related to earlier exposure of hemodynamic stress to septal wall.

CONCLUSION

Effective geometric and functional evaluation of initial remodeling due to hemodynamic stress is important according to both human and animal data. These findings possibly contribute to early recognition of adaptive phase of hypertensive remodeling and more effective management in a timely fashion.

Prediction of 8-year cardiovascular outcomes in patients with systemic arterial hypertension: value of stress (99m)Tc-tetrofosmin myocardial perfusion imaging in a high-risk cohort

OBJECTIVE

Systemic arterial hypertension is a strong and prevalent cardiovascular risk factor. Currently, information on the very long-term prognostic value of single-photon emission computed tomography (SPECT) myocardial perfusion imaging (MPI) in patients with systemic arterial hypertension is lacking. The aim of this study was to assess the value of stress (99m)Tc-tetrofosmin MPI for the prediction of very long-term outcome in these patients.

METHODS

The study population consisted of 608 patients with systemic arterial hypertension who underwent exercise or dobutamine stress (99m)Tc-tetrofosmin MPI for the assessment of known or suspected coronary artery disease. Follow-up was successful in 600 (99%) patients. The endpoints were all-cause mortality, cardiac death, nonfatal infarction, and coronary revascularization. Kaplan-Meier survival cures were constructed and univariate and multivariate analyses were performed to identify predictors of very long-term outcome.

RESULTS

The mean age of the patients was 59 ± 10 years, and 65% of them were male. MPI findings were normal in 301 patients (50%). Myocardial perfusion abnormalities were fixed in 162 (27%) and reversible in 137 (23%) patients. During a median 8.1-year follow-up, 241 (40%) patients died (121 cardiac deaths), 52 (9%) had a nonfatal myocardial infarction, and 128 (21%) underwent coronary revascularization. Survival curves in patients with a low vs a high summed difference score diverged up to 5 years after the test was performed. Multivariate analyses demonstrated that SPECT MPI provided incremental prognostic information up to 5 years after the test.

CONCLUSIONS

Stress (99m)Tc-tetrofosmin MPI provides incremental prognostic information for the prediction of cardiovascular outcome in patients with systemic arterial hypertension. Patients with normal stress MPI have a significantly better prognosis as compared with those with an abnormal study, up to 5 years after the test is performed.

Single-photon emission computed tomography myocardial perfusion imaging and the risk of sudden cardiac death in patients with coronary disease and left ventricular ejection fraction>35%

OBJECTIVES

The aim of this study was to determine whether single-photon emission computed tomography (SPECT) myocardial perfusion imaging (MPI) is an effective method of risk stratification for sudden cardiac death (SCD) in patients with coronary artery disease (CAD) and left ventricular ejection fraction (LVEF)>35%.

BACKGROUND

Most victims of SCD have an LVEF>35%.

METHODS

The study population included 4,865 patients with CAD and LVEF>35% who underwent gated SPECT MPI. We used Cox proportional hazard modeling to examine the relationship between patient characteristics and SCD.

RESULTS

The median age of the population was 63 years (25th, 75th percentile: 54, 71 years), and the median LVEF was 56% (25th, 75th percentile: 50%, 64%). The median follow-up for all patients was 6.5 years (25th, 75th percentile: 3.6, 9.3 years). During follow-up, there were 161 SCDs (3.3%). After multivariable adjustment, LVEF, the Charlson index, hypertension, smoking, antiarrhythmic drug therapy, and the summed stress score (SSS) were associated with SCD (all p<0.05). For each 3-U increase in the SSS, the hazard ratio for SCD was 1.13 (95% confidence interval: 1.04 to 1.23). The addition of perfusion data to the clinical history and LVEF was associated with increased discrimination for SCD events (c-index 0.728). Risk stratification with a derived SPECT nomogram did not result in statistically significant net reclassification improvement (p=0.26) or integrated discrimination improvement (p=0.38).

CONCLUSIONS

Among patients with CAD and LVEF>35%, the extent of stress MPI perfusion defects is associated with an increased risk of SCD. Future large prospective studies should address the role of perfusion imaging in the identification of high-risk patients with LVEF>35% who might benefit from ICD implantation.

The hypertensive heart. An integrated understanding informed by imaging

Clinical sequelae of hypertension include heart failure, arrhythmias, and ischemic events, especially myocardial infarction and stroke. Recognizing the hypertensive heart has diagnostic as well as prognostic implications. Current imaging techniques offer noninvasive approaches to detecting myocardial fibrosis, ischemia, hypertrophy, and disordered metabolism that form the substrate for hypertensive heart disease. In addition, recognition of aortopathy and atrial myopathy as contributors to myocardial disease warrant incorporation of aortic and atrial functional measurements into a comprehensive understanding of the hypertensive heart.

Noninvasive techniques to assess myocardial ischemia in hypertensive patients

Hypertensive patients are more affected by coronary artery disease (CAD) than normotensive patients. Currently, established techniques are able to diagnose myocardial ischemia/CAD in hypertensive patients with suspected CAD. An irrevocable role remains for exercise electrocardiogram (ECG) owing to the many parameters evaluated under physiologic conditions. However, the suboptimal specificity of a positive exercise ECG demands further examination of hypertensive patients with either myocardial single-photon emission computed tomography (SPECT) or stress echocardiography, both more specific than exercise ECG in diagnosing CAD. The high specificity of imaging techniques also makes them highly predictive of cardiac events. Additional techniques to help diagnose CAD are available. Tissue Doppler imaging, strain and other echo-derived techniques may add quantitative elements to recognize CAD in hypertensive hearts. The accuracy of MRI is improving to study myocardial function and perfusion. Positron emission tomography and multislice computed tomography, also in-built with fusion scanners, are playing roles in combining coronary angiography and myocardial function/ischemia assessment. However, no significant application of these additional techniques is available for hypertensive patients. Epicardial CAD assessed by coronary angiography remains the gold standard to decide for revascularization procedures. The presence of microcirculatory dysfunction, a symptom typical of hypertensive hearts, is opening up new areas of noninvasive diagnostic techniques for the detection of coronary flow reserve (CFR) and related myocardial ischemia. The quantification of CFR may render this parameter pivotal to deciding the need for revascularization procedures of intermediate coronary stenosis and it may become an additional gold standard in evaluating coronary vessels. Moreover, even with normal epicardial coronary arteries, microcirculation dysfunction bears prognostic stratification capabilities for hypertensive patients and it may become a promising therapeutic target in the near future.

Single-photon emission computed tomography myocardial perfusion defects are associated with an increased risk of all-cause death, cardiovascular death, and sudden cardiac death

BACKGROUND

Single-photon emission computed tomography myocardial perfusion imaging defects are associated with increased all-cause mortality and cardiovascular death. However, it is unknown whether single-photon emission computed tomography myocardial perfusion imaging can identify patients at increased risk of sudden cardiac death (SCD).

METHODS AND RESULTS

We analyzed a cohort of 6383 patients with angiographically documented coronary artery disease who underwent single-photon emission computed tomography imaging. Cox proportional hazards modeling was used to examine the relationship between patient characteristics and SCD. Among patients who died, the median time to SCD was 2.7 years (25(th), 75(th) percentiles 0.9, 4.9, respectively). The incidence of SCD was 3.4% (n=215) over 6.1 years (25(th), 75(th) percentiles 3.7, 9.2, respectively) of follow-up. Patients with SCD had more severe heart failure symptoms, greater comorbidity (Charlson index), and higher summed stress perfusion scores (all P<0.001). After adjusting for left ventricular ejection fraction and other clinical factors in the multivariable model, the summed stress perfusion score (fixed plus reversible defects) remained significantly associated with the occurrence of SCD: summed stress perfusion score (hazard ratios per 3 U: 1.16 [95% CI, 1.08 to 1.25], P<0.001), left ventricular ejection fraction (hazard ratios per 5 U: 0.90 [95% CI, 0.85 to 0.95], P<0.001), and Charlson index (hazard ratios 1.35 [95% CI, 1.23 to 1.49], P<0.001).

CONCLUSIONS

Myocardial perfusion imaging is a significant predictor of SCD and provides information independent of clinical history and left ventricular ejection fraction. Gated single-photon emission computed tomography imaging, which evaluates both myocardial perfusion and function, may represent a more effective means of risk stratification than solitary left ventricular ejection fraction determination and should be evaluated in prospective trials.

The expanding role of left ventricular functional assessment using gated myocardial perfusion SPECT: the supporting actor is stealing the scene

BACKGROUND

Gating of single-photon emission computed tomography (SPECT) has significantly improved the reliability and diagnostic accuracy of myocardial perfusion imaging. The functional parameters derived from this technique, mainly left ventricular volumes and ejection fraction, have been demonstrated to be accurate and reproducible. They are able to increase the detection of severe and extensive coronary artery disease and show a significant incremental prognostic power over perfusion abnormalities. Therefore, the importance given to gated SPECT functional data has progressively grown.

DISCUSSION

This circumstance has further expanded the indications for myocardial perfusion imaging and strengthened its position among the different imaging modalities. Moreover, several studies show that the evaluation of ventricular function may have a leading part in justifying the execution of perfusion scintigraphy in various clinical conditions.

AIM

Aim of this review is to describe this evolution of gated SPECT functional assessment from a supporting rank with respect to perfusion, to a main actor position in the field of cardiac imaging.