Densitometric regional ejection fraction: a new three-dimensional index of regional left ventricular function--comparison with geometric methods

Central and peripheral adaptations after 12 weeks of exercise training in post-coronary artery bypass surgery patients

PURPOSE

Training adaptations in patients with coronary artery disease (CAD) have been reported previously, but little is known about central and peripheral adaptations in those recovering from coronary artery bypass graft surgery (CABG). The purpose of this study was to examine the effects of 12 weeks of endurance exercise training on exercise performance and left ventricular and peripheral vascular reserve in a group of uncomplicated CABG patients.

METHODS

Thirty-one patients were recruited and began training 8 to 10 weeks after uncomplicated CABG. Patients underwent progressive exercise training consisting of walking and jogging, at 75% to 80% maximal oxygen intake (VO2max). Measures of left ventricular function included ejection fraction (EF), ventricular volumes, and the pressure volume ratio, an index of contractility. Peak ischemic exercise calf blood flow and vascular conductance was determined using strain-gauge plethysmography. Maximal oxygen intake and submaximal blood lactate concentration also was determined.

RESULTS

A significant improvement in VO2max (1497 +/- 60 mL/min versus 1691 +/- 71 mL/min) was observed after training. This change was accompanied by an increase in the EF during submaximal exercise (60 +/- 3% versus 63 +/- 2% at 40% VO2max; 61 +/- 3% versus 64 +/- 3% at 70% VO2max) (P < 0.05), and the change in EF from rest to exercise (delta EF). No changes were observed for ventricular volumes during exercise, although there was a trend for a higher stroke volume at 70% VO2max. A significant increase (18%) was observed for peak ischemic exercise calf blood flow and vascular conductance. In addition, submaximal blood lactate concentration was lower after training.

CONCLUSIONS

These data indicate that exercise training for 12 weeks in patients recovering from CABG can elicit significant improvements in functional capacity that, for the most part, are secondary to peripheral adaptations, with limited support for improvement in left ventricular function.

The influence of myocardial systolic shortening on action potential duration following changes in left ventricular end-diastolic pressure

INTRODUCTION

Contraction-excitation feedback may be an important factor in arrhythmogenesis in patients with heart failure. We have previously demonstrated the contrasting effects of raising left ventricular end-diastolic pressure on action potential duration in dog and guinea pig hearts. The current study was undertaken to assess whether these differing effects might reflect differences in the effect of varying left ventricular end-diastolic pressure on systolic shortening in the two models.

METHODS AND RESULTS

Two models were studied and compared. In open chest dog hearts and isolated guinea pig hearts, measurements of myocardial segment length were made while left ventricular end-diastolic pressure was raised and lowered at constant left ventricular peak systolic pressure. Action potentials were also recorded while left ventricular end-diastolic pressure was changed. The dog hearts were studied further in a manner aimed at reproducing the contraction pattern of the guinea pig hearts. In the in situ dog heart, elevation of left ventricular end-diastolic pressure, and the consequent increase in end-diastolic segment length, was accompanied by a marked increase in systolic shortening, such that minimum systolic segment length remained unchanged. Elevation of left ventricular end-diastolic pressure was accompanied by a prolongation of action potential duration. In the in vitro guinea pig model, elevation of left ventricular end-diastolic pressure was accompanied by more modest changes in systolic shortening, which were not sufficient to compensate for increased diastolic segment length. Consequently, minimum systolic segment length increased as the hearts dilated. Elevation of left ventricular end-diastolic pressure was accompanied by a shortening of action potential duration. In a further series of experiments, the effects of increased left ventricular end-diastolic pressure were studied in the dog model while allowing aortic pressure to rise, thereby restricting systolic shortening. Under these circumstances, the dog model was similar to the guinea pig model, with an increase in left ventricular end-diastolic pressure causing a shortening of action potential duration.

CONCLUSION

Our results suggest that the effects of preload changes on action potential duration depend on accompanying changes in systolic shortening. This suggests a possible role for contraction-excitation feedback in arrhythmogenesis in patients with regional wall-motion abnormalities.

Improved densitometric measurement of left ventricular ejection fraction using dual-energy digital subtraction angiography

The effects of misregistration artifacts and background corrections on the densitometric measurement of left ventricular ejection fraction (EF) from digital subtraction angiography (DSA) images were studied in 20 patients. Densitometric ejection fraction measurements were performed on both conventional time subtraction images and on dual-energy subtraction images. Dual-energy subtraction is not sensitive to the motion induced artifacts which often mar time subtraction images. While the time subtraction images had varying degrees of misregistration artifacts, none of the dual-energy studies contained significant misregistration artifacts. Densitometrically determined ejection fractions measured with and without correction for background signals were compared. Poor agreement between time subtraction ejection fractions determined with and without background correction (EFNO-BKG = 0.88 EFBKG - 6.0%, SEE = 8.1%, r = 0.83) demonstrated the sensitivity of time subtraction EFs to the performance of a background correction procedure. Conversely, densitometric measurement of ejection fraction using dual-energy subtraction was significantly less sensitive to the performance of a background correction (EFNO-BKG = 0.99 EFBKG - 5.3%, SEE = 4.3%, r = 0.96). Since background correction requires accurate definition of ventricular borders, but motion artifacts often preclude accurate border definition, it is concluded that dual-energy subtraction is a significantly more robust method for measuring left ventricular ejection fraction using densitometry. It is further concluded that identification of the systolic endocardial border is not required when performing densitometric EF measurements on dual-energy images. Drawing of the end-diastolic border alone is sufficient to produce an accurate ejection fraction measurement.

Densitometric assessment of regional left ventricular systolic function during graded ischemia in the dog by use of dual-energy digital subtraction ventriculography

Densitometric analysis of images obtained by digital subtraction angiography (DSA) allows for more reproducible and less operator-dependent quantitation of ventricular function. Conventional DSA uses temporal subtraction but is limited by misregistration artifacts. Dual-energy digital subtraction angiography (DE-DSA) is immune to such misregistration artifacts. The ability of DE-DSA to quantitate changes in regional ventricular volume resulting from ischemia was tested. Densitometric analysis of both phase-matched and ejection fraction DE-DSA images was used to quantitate regional left ventricular systolic function during four levels of ischemia ranging from mild to severe in open-chest dogs (n = 10). DE-DSA left ventriculograms were obtained by means of central venous injections of iodinated contrast medium. Ischemia was graded according to percentage of systolic wall thickening as measured by sonomicrometry. Phase-matched end-systolic images were obtained at each of four levels of ischemia by subtracting an end-systolic control image from each end-systolic ischemic image. Ejection fraction images were obtained at the control level and at each level of ischemia by subtracting an end-systolic image from an end-diastolic image of the same cardiac cycle. The resulting wall motion difference signals represent the changes in regional ventricular volumes and were quantitated by densitometry. Densitometry was able to detect the effect of all levels of ischemia on regional function, even the mildest. Densitometric analysis of both phase-matched and ejection fraction DE-DSA images provides a sensitive technique for detecting and quantitating the changes in regional left ventricular systolic volume that occur with ischemia.

Time-course of left atrial performance during coronary artery occlusion followed by reperfusion in anesthetized dogs by densitometric analysis of digital atrioventriculographic images

The left atrial (LA) function during coronary artery occlusion followed by reperfusion using densitometric analysis of digital atrioventriculographic images was evaluated. Eight anesthetized dogs underwent atrioventriculography at baseline, 10 and 60 min after left circumflex coronary artery (LCX) occlusion and 5, 30, 60, and 120 min of reperfusion. Time-density curves were obtained for LA and left ventricle (LV). The ratios of passive atrial video-densitometric change (VC) to total VC (Passive Ratio), and active VC to total VC (Active Ratio) were calculated. Left ventricular ejection fraction (LVEF), peak ejection rate (PER), and peak filling rate (PFR) were derived. Active Ratio, an index of atrial contraction, increased to 144%, and Passive Ratio decreased to 75% of baseline at 60 min of LCX occlusion. Two hours after reperfusion, both Active and Passive Ratios returned to control level. While LVEF reduced to 70%, PER to 67%, LV peak positive dP/dt to 88% of baseline at 60 min after occlusion, and remained depressed at 2 h after reperfusion. However, PFR, LV peak negative dP/dt and LV isovolumic pressure decay rate showed recovery at 2 h after reperfusion. There were significant correlations between PFR and Passive Ratio (r = 0.41), and between Active and Passive Ratios (r = 0.55). Thus, time-course of recovery of LV post-ischemic systolic and diastolic function was different. Return of LA function to control level during 2 h after reperfusion may be depend on recovery of LV diastolic function.

Determination of cardiac ejection and valvular regurgitant fraction by on-line digital densitometry--methodology, validation, and application

Videodensitometry allows to obtain both left and right ventricular ejection fraction (EF) and aortic or pulmonary regurgitant fraction (RGF) from the wash-out curve of contrast medium. We developed this technique to digital densitometry and integrated it in the standard digital image acquisition system 'Digitron' using Siemens user's library. Sources of error like scatter radiation, veiling glare, accumulation of iodine in tissue, and inhomogeneous contrast mixing were considered by using ECG gated image subtraction, background reference regions, data fit to ideal wash-out curves and calculation of EF and RGF exclusively from density differences. The method was validated by phantom studies in which simulated angiocardiograms were generated with given values of EF (50 to 70%) and RGF (0 to 45%). The results tended to overestimate RGF by up to 10 percent points, when image contrast was high and the ventricle was masked poorly by the lead shutters. In the clinical setting, the reliability of the results can be judged from the fit of the wash-out curve presented automatically on the screen on a semi-logarithmic scale. The technique is available to the physician in the catheterization laboratory on-line during or immediately after the examination, which facilitates routine use.

Ischemic heart disease and regional left ventricular wall motion: a study comparing radial, centerline and a video intensity based slope technique

Left ventricular regional wall motion in ischemic heart disease was evaluated and compared using three different methods based on radiographic ventriculograms. Radial method uses an internal reference system, and centerline method employs an external reference system, both methods are based on two frame analysis. The last method, an automated video intensity technique, analyzes on a frame by frame basis utilizing an external reference system. A total of 42 patients were included in the study, of these 12 had a history of myocardial infarction. Significant coronary artery stenosis was defined as 50% measured diameter reduction. Right coronary artery (29/42) was most commonly involved. Single vessel disease was present in 18 patients, two vessel disease in 15 and three vessel disease in eight patients. The radial method detected abnormal wall motion in 16/42 patients, centerline method yielded a detection accuracy of 22/42 and with the new technique, asynchrony was noted in 39/42 patients. All three methods detected regional wall motion abnormalities with a higher sensitivity in patients with prior myocardial infarction. The centerline method had highest sensitivity for the right coronary artery bed (55%). The radial method (45%) and the video intensity based technique (95%) had the highest sensitivity for regions supplied by the left anterior descending artery.

A new video intensity based wall motion analysis technique

A new computerized video intensity based method to evaluate regional wall motion for a frame by frame analysis has been developed. A region of interest is defined, and its average time-intensity curve is computed for the cardiac cycle. For each time interval the video intensity for a pixel in the region of interest is correlated with the average for the whole ventricle and its slope and correlation coefficient are calculated to derive two functional images. This technique utilizes images either from levophase or direct opacification of the left ventricle, and it is insensitive to RR-interval changes.

Quantitative assessment of regional left ventricular function by densitometric analysis of digital-subtraction ventriculograms: correlation with myocardial systolic shortening in dogs

Conventional wall motion analysis of contrast ventriculograms assesses only that part of the wall that is tangential to the x-ray beam. To assess regional left ventricular function in three dimensions, a new computerized method based on densitometric analysis of digital subtraction left ventriculograms was developed and validated in nine open-chest dogs instrumented with a circumflex coronary artery occluder and sonomicrometers in the anterior and posterior walls. Each dog underwent digital subtraction ventriculography at baseline and at five levels (I to V) of dysfunction of the inferior wall induced by progressive stenoses of the circumflex coronary artery. The ventriculogram was divided into six segments around the end-diastolic center of gravity. Time-volume curves were obtained by densitometry in the normal anterior and ischemic inferior segments containing the sonomicrometers. From these curves, regional ejection fraction (R-EF), regional peak ejection rate (R-PER), and regional phase (R-PH) and amplitude (R-AMP) of the first Fourier harmonic were derived. From baseline to level V of dysfunction, myocardial systolic shortening determined by sonomicrometry decreased by 124 +/- 34% of control (mean +/- SD; p less than .001) in the ischemic wall, while it increased by 12 +/- 19% (NS) in the normal wall. At the same time, R-EF, R-PER, and R-AMP decreased in the ischemic segment by 65 +/- 12%, 46 +/- 30%, and 45 +/- 15% of control, respectively (all p less than .01), while they remained unchanged or increased in the normal segment. R-PH was delayed by 14 +/- 5% (p less than .01) in the ischemic segment, but remained unchanged in the normal segment, reflecting the asynchrony of regional left ventricular contraction during ischemia. Densitometric indexes of regional function correlated well with sonomicrometric systolic shortening both in normal and ischemic segments, with r values of .84 for R-EF, .80 for R-AMP, .64 for R-PER, and .55 for R-PH (all p less than .0001). Thus, densitometric analysis of digital subtraction left ventriculograms allows three-dimensional assessment of the extent, velocity, and synchrony of regional left ventricular contraction. Densitometric indexes of regional contraction correlate well with direct measurements of myocardial systolic shortening and are useful in quantitating regional left ventricular dysfunction.