Postexercise Images Research Articles

Abstract 12812: Creatine Chemical Exchange Transfer MRI Demonstrates Abnormal Calf Muscle Energetics in Peripheral Arterial Disease

Introduction: Creatine chemical exchange saturation transfer (CrCEST) is a novel MRI technique utilizing radiofrequency pulses to monitor creatine concentrations at high spatial resolution. The study utilized CrCEST kinetics to compare post-exercise creatine decay in peripheral arterial disease (PAD) patients to normal subjects and to validate against phosphocreatine (PCr) recovery by 31 phosphorus (P) MR spectroscopy (MRS). Methods: 23 subjects with PAD (claudication and ankle-brachial index<0.9) and 28 healthy subjects were enrolled. All underwent 3T MRI (Siemens Prisma) using a knee coil around the calf. Pre- and post-exercise images were obtained around plantar flexion ergometry (Ergospect) until exhaustion. Regions of interests were drawn around major muscle groups. Creatine decay times were obtained by fitting an exponential curve to the CrCEST values. 31 P spectra were obtained 20 minutes later at peak exercise using a surface-coil localized, free induction decay acquisition with 25 signal averages at a repetition time of 550s with calculation of PCr recovery time constant. Results: 23 PAD subjects (mean ABI 0.66 ± 0.11, age 64 ± 8, 17% females) had prolonged median overall calf muscle creatine decay time of 286 seconds (s) (Interquartile Range (IQR) 134 to 370) versus 152 s (IQR 114 to 193) in controls (age 63 ± 9, 70% females), p = 0.009. The gastrocnemius muscle demonstrated a creatine decay time of 316 s in PAD (IQR 189 to 510) versus 181 s in controls (IQR 102 to 236), p = 0.003 and the posterior tibialis muscle, 186 s (IQR 119 to 653) versus 125 s (IQR 72 to 221), p = 0.013. 8 PAD patients and 6 controls underwent CrCEST and 31 P MRS which were compared over the entire calf. Bland-Altman analysis (Figure 1B) yielded a mean difference of 71s (SD 109). Conclusions: Imaging with CrCEST demonstrates prolonged creatine kinetics in PAD patients compared to normal subjects with high spatial resolution and good agreement with 31 P MRS, although PCr recovery appears faster.

Thermal Imaging Following Exercise in Working Dogs.

Disaster search dogs traverse diverse and unstable surfaces found in collapsed buildings. It is unknown if the physical conditioning on a treadmill involves the same muscle groups that are involved in rubble search. This 14-week prospective cohort study was conducted to investigate changes within the thermal gradients of specific dog muscles following treadmill compared to rubble search. Nine dogs, ranging in age from 6 months to 4 years, were randomly assigned to one of two groups. Each week the two groups would participate in either 20 min of treadmill or rubble searches. Prior to exercise, the dogs were weighed and then kenneled in a temperature-controlled study room for 20 min at 21°C. Pre-exercise thermal images were then captured of the standing dog from the dorsal, left and right lateral, and caudal perspectives, and of the sitting dog from the rostral perspective. Following a 10-min warm-up period of stretches, dogs proceeded to either treadmill or search. Upon completion, dogs were kenneled in the study room for 20 min prior to post-exercise thermal images. Images were sectioned into 22 muscle regions, the pre-exercise images were subtracted from the post-exercise images to determine the temperature difference (ΔT) for that dog, on that day, for that activity. Thermography measures radiant energy, temperature, and converts this information into an image. This study looked at ΔT within a region pre and post-exercise. The study failed to find a statistically significant difference in the ΔT within each muscle group between treadmill and search activities. There was a decrease in ΔT within all muscle regions over the of the study except for the right cranial shoulder, right caudal shoulder, and right hamstring for the treadmill activity only. The decrease was significant in the pelvis, left longissimus, right cranial shoulder for the search activity, left oblique, left caudal shoulder, and left quadricep muscular regions. These findings suggest that ΔT in muscle groups are similar between treadmill exercise and rubble search. Regardless of the exercise type, 14 weeks of structured Search and Rescue training and treadmill exercise resulted in less ΔT associated with a structured weekly exercise.

A functional MRI Exploration of Hamstring Activation During the Supine Bridge Exercise.

The single leg supine bridge (SLB) is a commonly employed strengthening exercise and is used as a clinical test for hamstring function in sports, however, little is known about the patterns of muscle activation in this task. To explore these activation patterns, nine healthy, recreationally active males underwent functional magnetic resonance imaging (fMRI) of their thighs at rest and immediately after 5 sets of 10 repetitions of the SLB exercise. Exercise-induced increases in the transverse (T2) relaxation time of the biceps femoris long and short heads, semitendinosus and semimembranosus, were determined via signal intensity changes in pre- and post-exercise images and used as an index of muscle activation. The Bonferroni adjusted alpha was set at p<0.008. The semitendinosus exhibited a greater T2 increase than the biceps femoris short head (p<0.001, d=2.0) and semimembranosus (p=0.001, d=1.2), but not biceps femoris long head (p=0.029, d=0.9). Furthermore, the percentage change in T2 for biceps femoris long head was greater than its short head (p=0.003, d=1.4). During the SLB exercise, the semitendinosus is most selectively targeted and the biceps femoris long head is preferentially activated over its short head. These findings may have implications for the use of the SLB in hamstring injury prevention and rehabilitation programs.

Stress Echo Image Acquisition Quality is Dramatically Improved by a Novel Image Audit Program

Introduction: Timely acquisition of on-axis images with good endocardial visualisation is imperative for accurate interpretation of stress echocardiographic (SE) images and diagnosis of inducible ischaemia. Method: Quarterly image audits of 5% (n=636) of all SE (n= 12720) from April 2014 to December 2015 performed at HeartCare Partners were conducted by 2 randomly selected experienced sonographers. Peak-stress images were scored for endocardial definition (Wall Clarity Score (WCS): 0 inadequately visualised; 1 suboptimal definition; 2 well defined); on- vs. off-axis image obtained, and resting vs. peak-stress images matching. Result: Time taken to complete peak image acquisition from exercise cessation was <40s in 12%, 40-69s in 68% and <90s in the remainder. High quality peak-exercise endocardial definition was obtained overall (WCS: 1.83±0.04) with the inferior, inferoseptal and anteroseptal walls best visualised (WCS: 1.87±0.02), with the anterior, anterolateral and inferolateral walls proving more challenging (WCS: 1.80±0.02, p<0.001). Resting on-axis imaging improved from 82±5% to 91±2%. Peak images improved from 63±11% to 85±3% (p<0.001). Pre-/post-stress image matching improved across observation period (76±2% vs. 85±4%, p<0.05). Summary: Whilst previous stress echo validation studies have assessed diagnostic accuracy and inter-observer variability, the use of this novel image audit program has produced dramatic and clinically important improvements in endocardial definition, on-axis acquisition and pre-/post-exercise image matching.

Cardiopulmonary exercise testing in the MRI environment

Maximal oxygen consumption (max) measured by cardiopulmonary exercise testing (CPX) is the gold standard for assessment of cardiorespiratory fitness. Likewise, cardiovascular magnetic resonance (CMR) is the gold standard for quantification of cardiac function. The combination of CPX and CMR may offer unique insights into cardiopulmonary pathophysiology; however, the MRI-compatible equipment needed to combine these tests has not been available to date. We sought to determine whether CPX testing in the MRI environment, using equipment modified for MRI yields results equivalent to those obtained in standard exercise physiology (EP) lab.Ten recreationally trained subjects completed max tests in different locations; an EP laboratory and an MRI laboratory, using site specific equipment. CMR cine images of the heart were acquired before and immediately after maximal exercise to measure cardiac function. Subjects in all tests met criteria indicating that peak exercise was achieved. Despite equipment modifications for the MRI environment, max was nearly identical between tests run in the different labs (95% lower confidence limit (LCL) = 0.8182). The mean difference in max was less than 3.40 ml (kg/min)−1, within the variability expected for tests performed on different days, in different locations, using different metabolic carts. MRI performed at rest and following peak exercise stress indicated cardiac output increased from 5.1 ± 1.0 l min−1 to 16.4 ± 5.6 l min−1, LVEF increased from 65.2 ± 3.3% to 78.4 ± 4.8%, while RVEF increased from 52.8 ± 5.3% to 63.4 ± 5.3%. Regression analysis revealed a significant positive correlation between max and stroke volume (R = 0.788, P = 0.006), while the correlation with cardiac output did not reach statistical significance (R = 0.505, P = 0.137).max CPX testing can be effectively performed in the MRI environment, enabling direct combination of physiological data with advanced post-exercise imaging in the same test session.

Detection of post-exercise stunning by early gated SPECT myocardial perfusion imaging: Results from the IAEA multi-center study

BackgroundTransient post-ischemic LV dysfunction due to myocardial stunning in patients with coronary artery disease can be missed by conventional gated SPECT (GSPECT) acquisitions. The aim of this IAEA-sponsored multi-center study was to determine whether early post-exercise imaging is more likely to detect stunning than conventional without adversely affecting image quality or perfusion information. Methods and ResultsPatients undergoing exercise/rest GSPECT were enrolled in this international multicenter study. Post-exercise studies were acquired at 15 ± 5 minutes after radiotracer injection (Stress-1) and repeated at 60 ± 15 minutes (Stress-2). Rest studies (R) were acquired at 60 minutes post injection. A core laboratory quantitatively assessed perfusion pattern and LV blinded to the acquisition time. Ischemia was defined as summed stress score (SDS) ≥4, and stunning was defined as the difference between rest and post-stress LVEF (Δ-LVEF). In the 229 patients enrolled into the study, both image quality and perfusion information were similar between Stress-1 and Stress-2. Post-stress LVEF was associated with both ischemia and time of acquisition, with a significant correlation between SDS and Δ-LVEF, which was stronger at Stress-1 than Stress-2 in the ischemic compared to the non-ischemic population (r = 0.23 vs 0.08, P = 0.10). ConclusionsEarly post-exercise imaging is feasible, and can potentially improve the detection of post-ischemic stunning without compromising image quality and perfusion data

Peak Treadmill Exercise Echocardiography

Stress echocardiography is a useful tool for the clinical decision making process, given its accuracy and demonstrated prognostic value. Among available stress echocardiography techniques, exercise is safer and more physiologic, therefore must be considered the first choice for patients able to exercise. Peak exercise echocardiography has greater sensitivity than post-exercise imaging. Image quality of apical views at peak exercise is similar than that of images acquired during the immediate post-exercise period. Although more demanding than post-exercise treadmill imaging, the successfulness of peak treadmill exercise imaging may be improved with some skills. The role of new technology is promising for exercise echo. Doppler tissue and speckle imaging can assess myocardial velocities and deformation. However, although Doppler tissue imaging increases the agreement and accuracy among novel readers, it has not been demonstrated to be better than visual assessment when the latter is performed by experienced observers. Speckle imaging can easily measure myocardial torsion, which has been found to be altered under ischemic conditions. Finally, 3-dimensional echocardiography can also be used during exercise since a full volume of the entire myocardium can be obtained in a few cardiac cycles.

Prognostic value of peak and post-exercise treadmill exercise echocardiography in patients with known or suspected coronary artery disease

Although peak may have higher sensitivity than post-treadmill exercise echocardiography (EE) for the detection of coronary artery disease (CAD), its prognostic value remains unknown. We sought to assess the relative values of peak and post-EE for predicting outcome in patients with known/suspected CAD. We studied 2947 patients who underwent EE. Wall motion score index (WMSI) was evaluated at rest, peak, and post-exercise. Ischaemia was defined as the development of new or worsening wall motion abnormalities with exercise. Separate analyses for all-cause mortality and major cardiac events (MACE) were performed. Ischaemia developed in 544 patients (18.5%). Among them, ischaemia was detected only at peak exercise in 124 patients (23%), whereas 414 (76%) had ischaemia at peak plus post-exercise imaging and six patients (1%) had ischaemia only at post-exercise. During follow-up, 164 patients died. The 5-year mortality rate was 3.5% in patients without ischaemia, 15.3% in patients with peak ischaemia alone, and 14% in patients with post-exercise ischaemia (P < 0.001 normal vs. ischaemic groups). In the multivariate analysis, post-exercise WMSI was an independent predictor of MACE [hazard ratio (HR) 1.87, 95% confidence interval (CI) 1.09-2.19, P = 0.02]. Peak exercise WMSI was an independent predictor of MACE (HR 2.19, 95% CI 1.30-3.69, P = 0.003) and mortality (HR 1.58, 95% CI 1.07-2.35, P = 0.02). The addition of peak EE results to clinical, resting echocardiography, exercise variables, and post-EE provided incremental prognostic information for MACE (P = 0.04) and mortality (P = 0.04). Peak treadmill EE provides significant incremental information over post-EE for predicting outcome in patients with known or suspected CAD.

Peak treadmill exercise echocardiography: not feasible?: reply

We thank Dr Peteiro for the interest in our work. Exercise remains the cornerstone for the detection and prognostication of coronary artery disease, and its feasibility is very high when associated with stress echocardiography. We agree that regardless of the technique used, exercise echocardiography can be performed using either a treadmill or bicycle protocol. However, when treadmill exercise is performed, scanning during exercise is less feasible, so most protocols rely on post-exercise imaging.1 Here comes the real limitation of treadmill exercise echocardiography. In fact, it …

Evidence of pulmonary oedema triggered by exercise in healthy humans and detected with various imaging techniques

This review summarizes current literature on pulmonary oedema triggered by above-ground exercise in healthy humans from studies that use various imaging techniques to detect oedema. Eleven studies were identified, comprising of 137 subjects (mean age = 28 years). Eighty per cent (n = 110) were males, and 20% (n = 27) were female. The studies were grouped into three different categories according to the severity of the exercise protocol, which were either prolonged, submaximal exercise of 15-min to 2 h in duration at approx. 50-75%VO(2max) and not to exhaustion (PROLONGED, n = 44), a VO(2max) test lasting 16-20 min in which the intensity of exercise was only maximum for about 2 min at the end of the test (GXT, n = 15), and maximum or near maximum effort exercise protocols at or near volitional exhaustion where the goal was to finish in the fastest possible time or maintain the highest possible workload (MAX EFFORT, n = 78). Only 16% of the subjects showed signs of oedema from PROLONGED exercise and no subjects (0%) showed signs of oedema from GXT exercise. Surprisingly, approx. 65% of the subjects showed signs of oedema triggered by MAX EFFORT exercise (chi(2) test of association; P < or = 0.01), which was independent of both sex, the level of hypoxia (inspired PO(2) = 106-118 mmHg vs. 149 mmHg), the timing of the post-exercise imaging (<10, >30 but <60 min, or >60 min) and VO(2max) (approx. 3.0 vs. approx. 4.8 L min(-1)). The data suggests that the chances of triggering pulmonary oedema from exhaustive MAX EFFORT exercise is 4x more compared with PROLONGED exercise. As well, the likelihood of triggering pulmonary oedema may be independent of lung size, sex, moderate levels of hypoxia, and aerobic fitness.

Mapping activation levels of skeletal muscle in healthy volunteers: An MRI study

To use muscle functional MRI (mfMRI) to compare activation levels within and among triceps surae (TS) muscles. Seven healthy males performed five sets of 10 repetitions of a unilateral heel-raise exercise. T2-weighted images were obtained before and immediately after the exercise. Pixels that showed T2 greater than the mean +1 SD of the region of interest (ROI) in pre-exercise images and lower than the mean +1 SD of the ROI in post-exercise images were identified. The remaining T2 values in the post-exercise images were assigned to five categories indicated by color: red (highest level of activation), yellow, green, sky blue, and blue (lowest level of activation). The images were then used to construct three-dimensional (3D) images from which the volumes at each level of activation were determined. Within each of the TS muscles the % activated volumes with low and moderate levels of activation were larger than those with a high level of activation (P < 0.05). The % activated volumes with a high level of activation were larger in the medial gastrocnemius than the soleus (Sol; P < 0.05). The Sol had a larger % activated volume with a low level of activation than the lateral gastrocnemius (P < 0.05). Each activation level was nonuniformly distributed along the length within each TS muscle. There is substantial variation in the level of activation within and among the TS muscles; however, the activation level is mainly in the moderate to low range in all three muscles.

Load-Specific Distribution of Muscle Activity in Human Triceps Surae Muscles

Motor units are arranged topographically within some muscles, and are activated in the order of their size, which enables individual regions to be activated in contraction. The triceps surae muscles are composed of the gastrocnemius and soleus (Sol) muscles. The gastrocnemius contains a higher percentage of type II fibers than that in the Sol. We hypothesized that these two muscles show different distribution characteristics of muscle activity. PURPOSE: This hypothesis was tested by comparing three-dimensional (3-D) distribution of muscle activity in the medial gastrocinemius (MG) and Sol during plantar flexion exercise at two different loads with use of muscle functional magnetic resonance imaging. METHODS: Six male subjects performed seven sets involved 10 repetitions of plantar flexion exercises with load that was 25 or 75% of their 12 repetitions maximum (RM). Transverse relaxation time (T2)-weighted images (repetition time 2500 ms; echo time 25, 80 ms; slice thickness 10 mm; gap 0 mm) were acquired from calf before and after each exercise load. To threshold images, considering as “active muscle” only those pixels showing T2 greater than the mean + 1SD of regions of interest (ROIs) in the pre-exercise images and a T2 lower than the mean + 1 SD of ROIs in the post-exercise images. Thresholded images were 3-D reconstructed, from which area of active muscle was determined along the x-axis (transversely), y-axis (longitudinally), and z-axis (vertically), respectively. RESULTS: The percentage area of activated muscle, which is relative to the anatomical cross-sectional area, was significantly larger after exercise with heavy load (75% of 12RM) than with light load (25% of 12RM) at each axis in the MG. On average, percentage area of activated muscle was 53.5 ± 6.4% in heavy load and 35.5 ± 3.3% in light load at x-axis (P< 0.05), 53.7 ± 6.9% in heavy load and 36.2 ± 3.0% in light load at y- axis (P <0.05), and 54.2 ± 4.8% in heavy load and 37.0 ± 3.7% in light load at z-axis (P <0.05). However, Sol did not show such differences. In the MG, distribution of muscle activity showed similar pattern between heavy and light loads along the x-axis and y-axis, but it varied across along the z-axis (P <0.05); it was higher at the proximal portion with greater load. No interactive effect was found at any axes in the Sol. CONCLUSION: Increase in load of repetitive plantar flexion exercises was accompanied by increased activations in the MG, especially at around the region of proximal portion and at throughout in a transversal and longitudinal axes. These findings suggest that load-specific distribution characteristics of muscle activity would be different between MG and Sol.

Quantitative assessment of skeletal muscle activation using muscle functional MRI

The purpose of the present study is to determine whether muscle functional MRI (mfMRI) can be used to obtain three-dimensional (3-D) images useful for evaluating muscle activity, and if so, to measure the distribution of muscle activity within a medial gastrocnemius (MG) muscle. Seven men performed 5 sets of 10 repetitions of a calf-raise exercise with additional 15% of body-weight load. Magnetic resonance images were obtained before and immediately after the exercise. To threshold images, only those pixels showing transverse relaxation time (T2) greater than the mean+1 S.D. of the entire regions of interest (ROIs) in the preexercise image and T2 lower than the mean+1 S.D. of the entire ROIs in the postexercise image were identified. The survived pixels showing T2 are defined as active muscle. Those thresholded images were 3-D reconstructed, and this was used to determine area of active muscle along transverse, longitudinal and vertical axes. At the exercise level used in the present study, the percentage volume of activated muscle in the MG was 62.8+/-4.5%. There was a significant correlation between percentage volume of activated muscle and integrated electromyography (r=.78, P<.05). Percentage areas of activated muscle were significantly larger in the medial than in the lateral region, in the anterior than in the posterior region and in the distal than in the proximal region (P<.05). These results suggest that mfMRI can be used to evaluate the muscle activity and to determine intramuscular variations of activity within skeletal muscle.

Muscle activation and its distribution within human triceps surae muscles

The purposes of this study were 1) to quantify the volume of activated parts within a whole muscle and 2) to examine activated area distributions along the length of muscle. Seven male subjects performed five sets of 10 repetitions of a single-leg calf-raise exercise with the knee fully extended. Transverse relaxation time (T2)-weighted spin echo images were acquired before and immediately after the exercise. A range of pixels with a T2 greater than the mean +1 SD of the region of interest (ROI) from the preexercise image and pixels with a T2 lower than the mean + SD of the ROI from the postexercise image were defined as "active" muscle. The active muscle images were three dimensionally reconstructed, from which the volume of the activated muscle was determined for individual triceps surae (TS) muscles. Our data indicate that approximately 46% of the medial gastrocnemius (MG) muscle was activated during the exercise, with activation of the lateral gastrocnemius (LG) and soleus (Sol) muscles being approximately 35%. In the MG, distal portions had a greater percentage area of activated muscle than the proximal portions (P < 0.05), which was consistent with the results regarding electromyogram activity. In contrast, regional activation differences were not observed in the LG and Sol. These findings suggest that the amounts of activated muscle and its distribution would be different among TS muscles.

Three-dimensional Activation Properties Of Triceps Surae Muscles During Concentric And Eccentric Contractions Using Muscle Functional MRI

PURPOSE The purpose of this study is to compare activated areas and its distributions within a whole muscle between concentric and eccentric plantar flexions using muscle functional magnetic resonance imaging (mfMRI). METHODS Eight males performed maximum concentric and eccentric plantar flexion exercises separately for ten sets of 10 repetitions at an angular velocity of 30°/s on a Biodex isokinetic dynamometer. Transverse relaxation time (T2)-weighted mfMR images of the lower limbs (Spin-echo; repetition time 2500 ms; echo time 25, 80 ms; number of excitation 1; slice thickness 10 mm; slice interval 0 mm; scan time 5:30) were obtained before and immediately after exercise. Activated muscles were defined from within a range of pixels with a T2 greater than the mean +1 SD of the range of interest (ROI) from each preexercise images, and pixels with a T2 lower than the mean +1 SD of the ROI from each of the postexercise images. The active muscle images were three-dimensionally reconstructed, from which the activated muscle area and their distributions were determined. RESULTS The mean percentage volume of activated medial gastrocnemius (MG) and lateral gastrocnemius (LG) with concentric contractions were 46.5 and 49.7%, respectively, and were significantly higher (P < 0.05) than those with eccentric contraction (37.5% and 40.4%). No difference was observed in percent-activated volume of the soleus (SOL) between concentric (40.1%) and eccentric (40.3%) contraction. There were significant differences in relative activated area located distal parts for the MG and mid-belly parts for the LG between both contractions, but the SOL did not show such regional difference. CONCLUSIONS The results suggest that each TS muscles shows distinct amount of activation and their distribution profiles for the different types of muscle contraction.

Comparison of peak and postexercise treadmill echocardiography with the use of continuous harmonic imaging acquisition

Objectives We sought to compare the feasibility and accuracy of peak and postexercise treadmill echocardiography with the use of continuous harmonic imaging capture. Background Previous work has demonstrated the superiority of peak exercise echocardiography (EE) as compared with post-EE for the diagnosis of coronary artery disease (CAD). However, most of these studies used fundamental imaging and view-per-view acquisition systems. Technical advantages in stress echocardiography include harmonic imaging and continuous imaging capture. Methods The study group included 650 patients (423 men; 60 ± 12 years) who were submitted to peak and postexercise treadmill echocardiography. Results Postexercise images were acquired within 55 seconds after exercise (28 ± 10). The number of segments visualized in each view were similar at peak and post-EE except for the parasternal short-axis view, which was better qualified at postexercise. For analysis of diagnostic capability we included 312 patients: 195 were included on the basis of having had an EE and a coronary angiography, whereas 117 patients with pretest probability of CAD < 10% who had atypical chest pain or were asymptomatic were also included and considered as having no CAD. CAD (≥50% stenosis) was confirmed in 159 patients. Positive EE was defined as ischemia or necrosis. Sensitivity for CAD was higher with peak imaging (92% vs 77%, P < .001), with similar specificity (78% vs 87%, P = not significant) and accuracy (85% vs 82%, P = not significant). Conclusion Peak treadmill EE is technically feasible and has higher sensitivity for CAD than posttreadmill EE. Therefore, in the clinical setting, peak EE should be performed for diagnostic purposes.

Importance of wall motion analysis in the diagnosis of left main disease using stress nuclear myocardial perfusion imaging.

We describe a case of a 54-year-old male who underwent exercise technetium-99m sestamibi myocardial perfusion imaging prior to his renal transplantation. With exercise, the patient's myocardial perfusion imaging did not show any transient or fixed myocardial perfusion abnormalities due to balanced ischemia. However, wall motion analysis showed a new global left ventricular systolic dysfunction on post-exercise images. Coronary angiography showed severe left main coronary lesion involving ostia of left anterior descending, ramus intermedius and left circumflex coronary arteries with moderate right coronary artery disease. If one had used the perfusion imaging alone in this patient, the severe multivessel disease including left main coronary disease could have been missed. In this article we emphasize the importance of wall motion analysis in patients undergoing myocardial perfusion imaging.

Incidence and significance of ischemic ST-segment depression occurring solely during recovery after exercise testing

Although ischemic ST-segment depression (ST↓) during exercise testing is an accepted finding suggesting the presence of coronary artery disease (CAD), the significance of ST↓ that appears solely during the recovery period is less well defined. There have been only a few studies1–5 addressing this issue. Only 1 study correlated ST↓ in recovery with scintigraphic incidence of ischemia, and that study used planar thallium-201 (Tl-201) imaging.3 Tl-201 imaging usually begins as soon as possible after exercise testing, making it difficult to perform careful postexercise electrocardiographic (ECG) monitoring. Technetium-99m (Tc-99m) sestamibi single-photon emission computed tomography (SPECT) is superior to Tl-201 in this regard because Tc-99m sestamibi does not rapidly redistribute. This yields ample time for poststress ECG monitoring before acquiring postexercise images. Therefore, the purpose of this study was to comprehensively investigate this uncommon ECG response of recovery ST↓ using ECG-gated SPECT Tc-99m sestamibi imaging for determining the incidence of ischemic exercise test responses.

Postexercise left ventricular function: A comparative assessment by different noninvasive imaging modalities

The variety of noninvasive imaging modalities now available permits assessment of different aspects of left ventricular function in the postexercise state. Some of these modalities, such as first-pass radionuclide ventriculography, permit a nearly instantaneous assessment of left ventricular function in the early postexercise state. These modalities indicate that most exercise-induced left ventricular wall motion abnormalities resolve quickly after exercise. Resting wall motion abnormalities may also improve in the postexercise period; this response indicates the presence of hibernating myocardium capable of improving in response to myocardial revascularization procedures. On the other hand, all imaging techniques indicate that a certain percentage of exercise-induced wall motion abnormalities may persist into the postexercise period, and this finding signifies that severe coronary disease subtends the region of persisting wall motion abnormality. Further, if there is increased left ventricular size after exercise, both extensive and severe coronary disease are present. A conceptual framework for unifying these disparate findings is provided. These results underscore the importance of postexercise imaging in enhancing clinical assessment and imply that there are important technical considerations to contemplate when performing certain tests such as postexercise echocardiography. Copyright © 2001 by W.B. Saunders Company

Immediate thallium re-injection after stress imaging for the detection of myocardial viability.

Myocardial perfusion imaging with thallium is an established method to assess the presence of ischaemic and viable myocardium. Using planar imaging, images acquired 1 h after immediate thallium re-injection have been shown to be comparable to those of 3 h redistribution. The aim of this study was to clarify this using SPET. Twenty patients with chronic coronary artery disease with at least two perfusion defects on post-exercise images participated in this study. All patients received thallium re-injection after post-stress SPET and all had 1 h, 3 h and 24 h redistribution imaging. The thallium myocardial tomograms were divided into 14 segments for each patient. A total of 78 segments were studied. When the frequency of reversibility on 1 h, 3 h and 24 h redistribution images is compared, of the 78 SPET defects 18 (23.1%) showed reversibility by 1 h, 34 (43.6%) by combined 1 h and 3 h imaging (P < 0.05) and 50 (64.1%) by combined 1 h, 3 h and 24 h imaging (P < 0.05). Our results show that, compared to 3 h images, images acquired 1 h after immediate thallium re-injection underestimate the extent of viable myocardial segments and the incidence of late reversibility was not reduced by the immediate re-injection of thallium.