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

Radiographic and echocardiographic evaluation in rescued Korean raccoon dogs (Nyctereutes procyonoides koreensis)

Introduction

Nyctereutes procyonoides koreensis (Korean raccoon dog), a member of the Canidae family, is anatomically similar to dogs. Previous studies have used vertebral heart scale measurements to measure the cardiac size of Korean raccoon dogs on thoracic radiographs; however, the use of additional cardiac size indices, such as vertebral left arial score, intercostal space, cardiothoracic ratio, and echocardiographic indices, has not been reported. Therefore, this study aimed to establish normal reference ranges for various thoracic radiographic and echocardiographic indices in normal Korean raccoon dogs.

Methods

Twenty-six Korean raccoon dogs (11 males and 15 females) were included in this study. The thoracic radiographic indices, vertebral heart scale score, and vertebral left atrial score were measured in the right lateral view. The intercostal space and cardiothoracic ratio were measured in the ventrodorsal view. The echocardiograms were evaluated in the right parasternal long and short axis view and left parasternal apical view.

Results

The mean values for the thoracic radiographic and echocardiographic indices were as follows: vertebral heart scale, 9.12 ± 0.74; vertebral left atrial score, 1.5 ± 0.31; intercostal spaces, 3.17 ± 0.34; cardiothoracic ratio, 0.69 ± 0.07; left atrial to aortic root ratio, 1.22 ± 0.14; main pulmonary artery to aorta ratio, 1.22 ± 0.14; left ventricular end-diastolic internal diameter normalized for body weight, 1.36 ± 0.19; end-diastolic volume index, 51.07 ± 19.6; end-systolic volume index, 16.54 ± 7.45; the peak velocity of early diastolic transmitral flow, 73.13 ± 15.46 cm/s; and the ratio between the transmitral flow velocities and the peak early diastolic velocity, 1.77 ± 0.47. Only percent increase in the left ventricular end-systolic internal diameter was negatively correlated with body weight. The remaining indices showed no correlations with body weight.

Conclusion

To the best of our knowledge, this is the first case report covering both thoracic radiographic and endocardiographic indices for Korean raccoon dogs. Thus, the thoracic radiographic and echocardiographic indices established in this study may be used to evaluate the cardiac condition of Korean raccoon dogs.

Validation of in vivo myocardial strain measurement by magnetic resonance tagging with sonomicrometry

OBJECTIVES

This study was designed to validate strain measurements obtained using magnetic resonance tagging with spatial modulation of magnetization (SPAMM). We compared circumferential segment shortening measurements (%S) obtained using SPAMM to sonomicrometry %S in a canine model with (n = 28) and without (n = 3) coronary artery ligation.

BACKGROUND

Magnetic resonance tagging enables noninvasive measurement of myocardial strain, but such strain measurements have not yet been validated in vivo.

METHODS

Circumferential sonomicrometry crystal pairs were placed in apical myocardium at ischemic risk in ligation studies and in adjacent and remote myocardium. The %S was obtained from closely juxtaposed sonomicrometry and SPAMM sites.

RESULTS

Paired data were available from 19 of 31 studies. Both methods distinguished remote from ischemic function effectively (p = 0.014 for SPAMM and p = 0.002 for sonomicrometry). SPAMM %S was similar to sonomicrometry %S in ischemic myocardium (2 +/- 3 vs. 0 +/- 3 p = 0.067) but was slightly higher than sonomicrometry %S in remote myocardium (11 +/- 10 vs. 7 +/- 5, p = 0.033). End-systolic (n = 30) and late systolic (n = 34) SPAMM %S correlated well with sonomicrometry %S (r = 0.84, p < 0.0001 and r = 0.88, p < 0.0001).

CONCLUSIONS

Magnetic resonance tagging using SPAMM can quantitate myocardial strain in ischemic and remote myocardium. This study validates its application in scientific investigation and clinical assessment of patients with myocardial ischemia.

Pacing-induced left ventricular asynchronies in dogs with critical coronary stenosis: mechanisms and effect of anesthetics

The mechanisms leading to left ventricular (LV) asynchronies are incompletely understood, and reports on the functional significance of asynchronies for the affected segments are conflicting. To characterize LV asynchronies, 16 anesthetized dogs with critical stenosis of the left anterior descending coronary artery (LAD) were instrumented to measure subendocardial contractile function (sonomicrometry) and the ECG in the LAD territory. The subendocardial ECG was also recorded from the anterior basal LV territory. Time of regional S wave arrival (TS) and time of onset of segment shortening were determined. The animals underwent atrial pacing with increasing frequencies until systolic LAD territory contractile dysfunction and eventual LV asynchronies were observed. Six animals without LAD stenosis served as controls to define the normal response (mean +/- 2.SD) to increasing pacing rates of systolic shortening and onset time of segment shortening (time difference between TS and onset of segment shortening). LAD contractile dysfunction was considered as a systolic shortening below the normal range, and LV asynchronies as an onset time of segment shortening above the normal range. When LV asynchronies occurred, onset time of segment shortening in the LAD territory was 80.1 +/- 4.9 ms versus 14.8 +/- 3.7 ms at control (P < 0.01); the time difference between S wave arrival in the LAD and circumflex territories, however, was unchanged. LV asynchronies were associated with marked LAD territory contractile dysfunction (systolic shortening of 9.6 +/- 0.8% v 21.0 +/- 1.9% at control, after systolic shortening of 31.3 +/- 3.8% v 9.0 +/- 2.6% at control; P < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Left ventricular volume determined echocardiographically by assuming a constant left ventricular epicardial long-axis/short-axis dimension ratio throughout the cardiac cycle

OBJECTIVES

The purpose of this study was to develop and test a simplified echocardiographic method to calculate left ventricular volume.

BACKGROUND

This method was based on the assumption that the ratio of the left ventricular epicardial long-axis dimension to the epicardial short-axis dimension was constant throughout the cardiac cycle. With use of this constant ratio, the method developed to calculate left ventricular volume at a given point in the cardiac cycle required the left ventricular endocardial long-axis dimension to be measured at only one point in the cardiac cycle.

METHODS

Studies were performed in 13 normal dogs, 8 normal puppies, 9 normal pigs, 12 dogs with aortic stenosis, 13 dogs with acute mitral regurgitation, 12 dogs with chronic mitral regurgitation, 7 dogs that had undergone mitral valve replacement and 6 pigs that had had chronic supraventricular tachycardia. Animals with aortic stenosis developed left ventricular pressure overload hypertrophy with a 60% increase in left ventricular mass; chronic mitral regurgitation caused left ventricular volume overload hypertrophy with a 46% increase in left ventricular volume; supraventricular tachycardia caused a dilated cardiomyopathy with a 55% decrease in left ventricular ejection fraction.

RESULTS

The left ventricular epicardial long-axis/short-axis dimension ratio remained constant throughout the cardiac cycle in each animal group. End-diastolic and end-systolic volumes calculated with the simplified echocardiographic method correlated closely with angiographically measured volumes; for end-diastolic volume, echocardiographic end-diastolic volume = 1.0 (angiographic end-diastolic volume) -1.8 ml, r = 0.96; for end-systolic volume, echocardiographic end-systolic volume = 0.98 (angiographic end-systolic volume) -0.7 ml, r = 0.95.

CONCLUSIONS

Thus the left ventricular epicardial long-axis/short-axis dimension ratio was constant throughout the cardiac cycle in a variety of animal species and age groups and in the presence of cardiac diseases that significantly altered left ventricular geometry and function. The simplified echocardiographic method examined provided an accurate determination of left ventricular volumes.

Left ventricular asynchrony: an indicator of regional myocardial dysfunction

There is a marked heterogeneity of myocardial wall thickening within the left ventricle and among different individuals. It is therefore difficult to detect regional myocardial dysfunction from absolute values of systolic wall thickening. We tested whether the extent of left ventricular asynchrony during ischemia and reperfusion can be used to quantify the severity of regional myocardial dysfunction when nonischemic baseline function is not known. In six anesthetized, open-chest dogs regional myocardial wall thickness was measured by means of sonomicrometry under control conditions, at three degrees of ischemic dysfunction (mild, moderate, and severe), and after release of a 15-minute occlusion of the left circumflex coronary artery, when degrees of moderate and mild reperfusion dysfunction similar to the preceding ischemic dysfunction were present. Two indexes of left ventricular asynchrony were calculated: (1) postejection thickening (PET) and (2) the phase difference of the first Fourier harmonic of posterior versus anterior myocardial wall motion (PD). Systolic myocardial wall thickening was decreased from 15.3 +/- 3.1 (standard deviation) % (control value) to 9.7 +/- 1.4% (mild ischemia), 4.2 +/- 1.6% (moderate ischemia), and -3.7 +/- 3.1% (severe ischemia). Conversely PET increased from 0.02 +/- 0.04 mm (control value) to 0.15 +/- 0.22 mm (mild ischemia), 0.19 +/- 0.15 mm (moderate ischemia), and 0.50 +/- 0.26 mm (severe ischemia). PD increased from 9 +/- 28 degrees (control value) to 22 +/- 19 degrees (mild ischemia), 54 +/- 18 degrees (moderate ischemia), and 107 +/- 21 degrees (severe ischemia). After release of the 15-minute left circumflex coronary artery occlusion, PET and PD recovered to 0.34 +/- 0.19 mm and 36 +/- 24 degrees (moderate dysfunction) and 0.25 +/- 0.31 mm and 29 +/- 8 degrees (mild dysfunction), respectively. There were inverse linear relationships between systolic wall thickening and PET (r = -0.86, p less than 0.001) and between systolic wall thickening and PD (r = -0.87, p less than 0.001). Inotropic stimulation by postextrasystolic potentiation increased regional systolic myocardial posterior and anterior wall thickening but did not alter the extent of left ventricular asynchrony. Thus, when normal baseline function is not known, the severity of regional myocardial dysfunction at a given inotropic state can be determined by analysis of left ventricular asynchrony. There was no significant correlation between the extent of PET and PD during ischemia and at early reperfusion and the recovery of contractile function at late reperfusion. Thus PET does not provide a prospective marker for the functional outcome of reperfusion.

Evaluation of parameters for the assessment of regional myocardial contractile function during asynchronous left ventricular contraction

The primary purpose of this study was to evaluate parameters used for the measurement of regional myocardial contractile function in the setting of left ventricular (LV) asynchrony. Secondarily, we tested whether the peak negative value of left ventricular dP/dt (-dP/dt) can be used to estimate global LV end-systole during asynchrony. In seven anesthetized (Isoflurane) swine the left anterior descending coronary artery was cannulated and perfused at constant blood flow rates. To produce LV asynchrony, dobutamine (D) was infused into the perfusion system. This was repeated later during coronary hypoperfusion (HYPO) sufficient to produce regional contractile dysfunction. The amount of LV wall thickening during systole (% WT, sonomicrometry) was calculated using either -dP/dt or the closure of the aortic valve (AO, electromagnetic flow probe) for estimating the timing of global LV end-systole. % WT was compared to other parameters which are not dependent upon the timing of global LV end-systole, including the amplitude of the first harmonic of the Fourier transform (AMP) and regional myocardial work (WI) estimated form the left ventricular pressure-wall thickness relationship. A close correlation between global LV end-systole defined by the AO or -dP/dt existed during control, D or HYPO. During HYPO + D no such relationship was found (r = .22, NS), and % WT calculated using -dP/dt as an estimate of end-systole was underestimated when compared to % WT calculated by use of the AO to estimate end-systole (2.9 +/- 6.8% vs 6.3 +/- 6.6%, p less than .05). % WT, AMP, and WI showed similar results during control, D and HYPO. However, During HYPO increased the AMP from .59 +/- .23 mm to .76 +/- .32 mm and WI from 67 +/- 20 mm Hg*mm to 95 +/- 24 mm Hg*mm (p less than .05), respectively. This increase in regional myocardial function, however, was not detected by % WT (10.5 +/- 6.4% vs 6.3 +/- 6.6%). Thus, during left ventricular asynchrony, the measurement of LV -dP/dt to estimate the timing of global LV end-systole is inappropriate and can lead to inaccuracies in the measurement of regional contractile function. Parameters such as AMP or WI are advantageous since global LV end-systole does not need to be accurately defined.