George D. Harp

Effect of endurance exercise training on heart rate variability at rest in healthy young and older men

Heart rate variability (HRV) (SD of the RR interval), an index of parasympathetic tone, was measured at rest and during exercise in 13 healthy older men (age 60 to 82 years) and 11 healthy young men (age 24 to 32 years) before and after 6 months of aerobic exercise training. Before exercise training, the older subjects had a 47% lower HRV at rest compared with the young subjects (31 +/- 5 ms vs 58 +/- 4 ms, p = 0.0002). During peak exercise, the older subjects had less parasympathetic withdrawal than the young subjects (-45% vs -84%, p = 0.0001). Six months of intensive aerobic exercise training increased maximum oxygen consumption by 21% in the older group and 17% in the young group (analysis of variance: overall training effect, p = 0.0001; training effect in young vs old, p = NS). Training decreased the heart rate at rest in both the older (-9 beats/min) and the young groups (-5 beats/min, before vs after, p = 0.0001). Exercise training increased HRV at rest (p = 0.009) by 68% in the older subjects (31 +/- 5 ms to 52 +/- 8 ms) and by 17% in the young subjects (58 +/- 4 ms to 68 +/- 6 ms). Exercise training increases parasympathetic tone at rest in both the healthy older and young men, which may contribute to the reduction in mortality associated with regular exercise.

Transaxial tomography with thallium-201 for detecting remote myocardial infarction: Comparison with planar imaging☆

Abstract Transaxial tomograhic imaging with thallium-201 was compared with standard, planar imaging in 38 patients with remote myocardial infarction and in 15 normal patients. Tomographic images were reconstructed from 64 views collected by a gamma camera that rotated about the anterior circumference of the patients chest. A series of consecutive transverse-section images which encompassed the cardiac volume were reconstructed at a 6 mm plane spacing by filtered back-projection. No correction was made for attenuation losses. The set of transverse-section images was reformatted by 3-dimensional interpolation to obtain tomograms along the long and short axes of the myocardium. Tomographic and planar images were interpreted qualitatively. Overall, tomography detected 33 of 38 (87%) prior infarctions whereas planar imaging detected 24 of 38 (63 %) (p = 0.01). Improvement of the tomographic imaging method occurred only in the combined subset of transmural inferior and subendocardial infarctions, and not in transmural anterior infarctions. Peak increases in creatinine phosphokinase were smaller in patients detected only by tomography compared with those detected by both the planar and the tomographic approach (3.1 × normal versus 10.4 × normal, p = 0.04). Five patients (13%) with prior infarction were not detected by either approach. For 6 of the 9 patients detected by tomography alone, realignment of the image data along the short and long axes of the heart was essential for making the diagnosis. Fourteen of 15 patients without infarction were normal on both planar and tomographic imaging. A single normal patient had a defect detected by both techniques, yielding a specificity of 93% for each. We conclude that transaxial tomography significantly improves the detection of thallium-201 myocardial perfusion defects in patients with prior myocardial infarction.

Left ventricular volume determination using single-photon emission computed tomography

A new method for measuring left ventricular (LV) volume based on gated single-photon emission computed tomography (SPECT) is described. Preliminary phantom studies showed an excellent correlation between SPECT and observed volumes (r = 0.99, standard error of the estimate [SEE] = 4.9 ml). SPECT was performed 24 hours after biplane contrast LV angiography in 36 patients. Transaxial blood pool tomograms were reconstructed by filtered back projection and reoriented to views orthogonal to the cardiac axes. Volume was calculated from serial short-axis tomograms by determining the base, apex and lateral borders of the LV blood pool, ascertaining the number of pixels in this volume and multiplying by the known volume of a pixel. Gated SPECT volumes were compared with contrast angiographic volumes. At end-systole, r = 0.96 and SEE = 12 ml; at end-diastole, r = 0.81 and SEE = 27 ml. For ejection fraction, r = 0.85 and SEE = 0.06. To test interobserver variation in processing, count data from 5 patients were processed twice (r = 0.98, SEE = 8.3 ml). There is an excellent correlation between SPECT and contrast angiographic volumes at end-systole; at end-diastole the relation is good. SPECT requires no arbitrary background correction, allows systematic isolation of the left ventricle from other overlapping cardiac chambers and requires no geometric assumptions for volume determination. It has promise as a direct method for measuring LV volume in a minimally invasive manner.

Quantitative gated blood pool tomographic assessment of regional ejection fraction: Definition of normal limits

OBJECTIVE Our aim was to select a method of analysis for gated blood pool tomography that reduced variability in a group of normal subjects, allowed comparison with normal limit files and displayed results in the bulls-eye format. BACKGROUND Abnormalities in left ventricular function may not be accurately detected by measures of global function because hyperkinesia in normal regions may compensate for abnormal regional function. Gated blood pool tomography acquires three-dimensional data and offers advantages over other noninvasive modalities for quantitative assessment of global and regional function. METHODS Alternative methods for selecting the ventricular axis, calculating regional ejection fraction and choosing the number of ventricular divisions were studied in 15 normal volunteers to select the combination of parameters that produced the lowest variability in quantitative regional ejection fraction. Methods for quantitative comparison of regional ejection fraction with normal limit files and for display in the bulls-eye format were also examined. RESULTS A fixed axis (the geometric center of the ventricle defined for end-diastole and used for end-systole) gave ejection fractions that were significantly higher in the lateral wall versus in the septum, 82 +/- 8 (mean +/- 1 SD) versus 39 +/- 17 (p less than 0.001) at the midcavity and 66 +/- 11 versus 21 +/- 20 (p less than 0.001) at the base. A floating axis system (axis defined individually for end-diastole and end-systole and realigned at the center) gave more uniform regional ejection fraction: 63 +/- 6 versus 64 +/- 8 (p = NS) at the midcavity and 44 +/- 16 versus 45 +/- 15 (p = NS) at the base. The coefficient of variability for regional ejection fraction was consistently lower using a floating axis. Calculating regional ejection fraction by dividing the regional stroke volume by the end-diastolic volume of the region gave a lower coefficient of variability and a more easily understood value than dividing the regional stroke volume by the total end-diastolic volume of the ventricle. Although the variability was lower using five versus nine ventricular divisions, nine regions offer greater spatial resolution. Comparison of regional ejection fraction with normal data identified regions greater than 2.5 SD below the mean as abnormal. We described the two-dimensional bulls-eye format as a method for displaying the regional three-dimensional data and illustrated abnormalities in patients with prior myocardial infarction. CONCLUSIONS Gated blood pool tomography performed using a floating axis system, regional stroke volume calculation of ejection fraction and nine regions uses all the three-dimensional blood pool data to calculate regional ejection fraction, allow quantitative comparison with normal limit files, display the functional data in the two-dimensional bulls-eye format and demonstrate abnormalities in patients with myocardial infarction.

Evaluation of myocardial perfusion and function by single photon emission computed tomography

Although planar radionuclide techniques provide accurate, noninvasive measurements of myocardial perfusion and function that are of proven clinical value in the evaluation of the cardiac patient, they are limited by poor object contrast and superimposition of surrounding structures. Due to incomplete angular sampling and significant longitudinal distortion, limited angle tomography did not solve these problems. Single photon emission computed tomography (SPECT) can acquire scintillation information over very small angles of rotation and, thus, improve both object contrast and delineation of overlying or adjacent structures without distortion. The early SPECT systems were cumbersome, dependent on individual user developed software, and had extremely long acquisition and processing time. Improved camera design, new software algorithms, and the use of array processors have simplified and standardized quality control, decreased processing time, and minimized the number of user interventions. New image display formats and quantitative methods of analysis have made interpretation less cumbersome, more reliable and highly reproducible. Cardiac SPECT has been used with thallium-201 and gated blood pool imaging in both research and clinical applications and shown an improvement over planar methods of acquisition.

Rarity of preclinical alcoholic cardiomyopathy in chronic alcoholics <40 years of age☆

Abstract Preclinical alcoholic cardiomyopathy, myocardial damage in the absence of overt congestive heart failure in chronic alcoholics, is well characterized at necropsy, but attempts to identify such a clinical entity before death have produced conflicting results. Studying subjects only at rest, the inclusion of older alcoholics and limitations of noninvasive techniques may explain some of the disagreement. To determine if preclinical alcoholic cardiomyopathy could be identified independent of the aforementioned limitations, 25 asymptomatic chronic alcoholics aged For comparison, an age-matched group of healthy control subjects was also studied. For alcoholics and control subjects at rest, mean ejection fraction (67 ± 7% vs 71 ± 6%) and diastolic peak filling rate (3.4 ± 0.6 vs 3.3 ± 0.6 end-diastolic volumes per second [EDV/s]) were similar. At peak exercise, the mean ejection fraction (83 ± 6 vs 82 ± 10), change in ejection fraction (14 ± 10 vs 14 ± 7) and peak filling rate (8.9 ± 2.0 vs 9.5 ± 1.9 EDV/s) were also similar, but ejection fraction failed to increase appropriately in 3 alcoholics (12%), suggesting possible stress-induced myocardial dysfunction. Left ventricular chamber size, fractional shortening, wall thickness and ventricular mass by echocardiography were similar in the alcoholic and control groups, as were red blood cell levels of selenium and thiamine. Repeat studies after 4 weeks of abstinence from alcohol showed persistence of the exercise-induced abnormal response in 2 of the 3 alcoholics. These data suggest that the occurrence of preclinical cardiomyopathy in young, asymptomatic chronic alcoholics is rare and may require exercise stress testing to be detected.