Evaluation of Left Ventricular Tei Index (Index of Myocardial Performance) in Healthy Dogs and Dogs with Mitral Regurgitation

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.

Changes in echocardiographic indices and left ventricular strain values by two-dimensional speckle-tracking echocardiography following pre-anesthetic oral pimobendan administration compared with intravenous pimobendan in dogs

Introduction

The effects of pre-anesthetic single-dose oral pimobendan during inhalational anesthesia, including the comparison with the effects of single intravenous pimobendan under anesthesia, remain unexplored. Therefore, this study aimed to determine changes in hemodynamic and echocardiographic parameters induced by pre-anesthetic administration of oral pimobendan under isoflurane general anesthesia and to compare them with those induced by intravenous pimobendan.

Methods

Thirteen clinically normal dogs (4 laboratory and 9 client-owned dogs) with no clinical signs and not on any medical treatment were included. Anesthesia was performed three times: no pimobendan (Control), oral pimobendan (PIMO PO, 0.3 mg/kg), and intravenous pimobendan (PIMO IV, 0.15 mg/kg). Echocardiographic and hemodynamic parameters were monitored at 30-min intervals in all groups.

Results

Compared to the Control group, end-systolic volume index (ESVI) and normalized left ventricular internal diameter at end-systole (LVIDSN) were significantly lower, and fractional shortening (FS) and ejection fraction (EF) were significantly higher in the PIMO PO and IV groups (p < 0.001). Global radial strain (GRS) was significantly higher in the PIMO PO and IV groups (p = 0.015).

Conclusion

Under general anesthesia, oral pimobendan preserved LV systolic and myocardial function in a manner comparable to intravenous pimobendan. Pre-anesthetic administration of oral pimobendan can be used to compensate for cardiac systolic function in dogs who require therapeutic and diagnostic procedures under general anesthesia with potential risk of circulatory failure.

Use of proposed systolic and myocardial performance indices derived from simultaneous ECG and PCG recordings to assess cardiac function in healthy Beagles

Background and Aim:

Cardiac time intervals (CTIs) can provide important information on the electrical and mechanical properties of the heart. We hypothesized that cardiac function can be described using the combined power of electrocardiography (ECG) and phonocardiography (PCG) signals. This study aimed to (1) validate a novel custom device in measuring CTI parameters; (2) compare CTI parameters with a commercially available device and standard transthoracic echocardiography (STE); and (3) compare calculated systolic performance index (SPI) and myocardial performance index (MPI) with Tei index from the STE.

Materials and Methods:

This study determined CTIs based on simultaneous ECG and PCG recordings in 14 healthy Beagle dogs using the custom-built device. These CTI parameters were compared with a commercially available device (Eko DUO ECG + Digital Stethoscope; Eko DUO) and the STE. Agreement of CTI parameters between the custom device and the commercially available device or STE was evaluated. Calculated SPI and MPI based on Wigger’s diagram were proposed, compared with SPI and Tei index, and correlated with STE parameters.

Results:

We found that the ECG and PCG parameters measured from the custom-built device did not differ from the commercially available device and the STE. By combining ECG and PCG signals, we established CTI parameters in healthy dogs including indices for systolic function (SPI: QS1/S1S2) and global cardiac function {F1 ([QS1+S2]/S1S2), F2 ([RS1+S2]/S1S2), and F3 (RS1 + [QS2-QT]/S1S2)}. The SPI, F2, and F3 were comparable with echocardiographic parameters describing systolic (Pre-ejection period/left ventricular ejection time [LVET]) and Tei index ([MCOdur-LVET]/LVET), respectively. Only SPI and F3 were correlated significantly with MCOdur and heart rate, respectively.

Conclusion:

We have validated the use of the custom-built device to describe CTIs that are comparable to the commercially available device and STE in healthy Beagles. The proposed SPI and MPI derived from CTI parameters can be useful in clinical practice to describe the cardiac function, especially in areas where access to STE is constrained.

Novel Approach to Assess Cardiac Function Using Systolic Performance and Myocardial Performance Indices From Simultaneous Electrocardiography and Phonocardiography Recordings in Dogs With Various Stages of Myxomatous Mitral Valve Disease

Background and Objective: Myxomatous mitral valve disease (MMVD) progression entails changes in the structural and functional properties of the heart affecting cardiac timings and intervals within the cardiac cycle. Conventionally, echocardiography is used to determine the cardiac time intervals (CTIs) including systolic and myocardial performance indices (SPI and MPI) in evaluating cardiac function. Alternatively, these CTIs can also be measured using simultaneous recordings of electrocardiography (ECG) and phonocardiography (PCG), but their values in different MMVD stages remain to be established. This study aimed to establish and prove the use of derived SPI and MPI from a dedicated device as a novel approach to assess cardiac function in different stages of MMVD dogs. Materials and Methods: A prospective study in 52 dogs with different MMVD stages measured the CTIs using a novel device. These were compared and correlated with standard echocardiographic parameters. The predictive value of SPI and three new proposed formulas to estimate MPI (i.e., F1, F2, and F3) in association with asymptomatic from symptomatic MMVD dogs were investigated. Results: Our findings revealed that CTI parameters measured from a novel device including QS1, QS2, S1S2, MPI-F1, and MPI-F2 were altered at different stages of MMVD. The SPI and all proposed MPI formulas were comparable with the systolic time interval and Tei index from echocardiography. In addition, the SPI, MPI-F1, and MPI-F2 were significantly correlated with the Tei index. However, the SPI was not able to differentiate the various stages of MMVD. Conversely, only the MPI-F1 (i.e., (QS1 + S2)/S1S2) demonstrated good predictive accuracy when compared between asymptomatic and symptomatic MMVD dogs similar to the Tei index. Moreover, this formula was able to differentiate stages B1 and C with remarkable predictive accuracy, higher sensitivity, and high specificity when compared with the Tei index. Conclusion: We have successfully described the CTI parameters in different MMVD stages using simultaneous ECG and PCG recordings in dogs. Furthermore, we have proven that the concept of using the newly proposed parameters from a novel device is equivalent to the Tei index. Thus, we established a novel approach to evaluate cardiac function and its supportive use in the diagnosis of MMVD patients.

An echocardiographic study of breed-specific reference ranges in healthy French Bulldogs

Echocardiography is a standard diagnostic tool for assessment of cardiac functions and cardiovascular diseases in dogs, however published echocardiographic measurements have varied widely based on dog breeds. The objective of this prospective reference interval study was to provide breed-specific echocardiographic values for healthy French Bulldogs. A total of 42 healthy French Bulldogs of both sexes (23 females and 19 males) were sampled. Furthermore, measurements for a control group (n = 16) were also conducted in four other dog breeds (Cocker Spaniel [n = 2], Cavalier King Charles Spaniel [n = 4], Terrier [n = 5], and Crossbreed [n = 5]). Standard M-mode, two-dimensional (2D), pulse wave (PW) Doppler, and tissue Doppler imaging (TDI) echocardiographic measurements were obtained from healthy French Bulldogs. The M-mode echocardiographic data obtained from French Bulldogs were compared to the data obtained from the control group. The left ventricular internal dimension at end-diastole (LVIDd; cm)/body surface area (BSA) (m² ) ratio for the study group was 3.35/0.53 = 6.32. Left ventricular measurements for French bulldogs and internal dimension at end-systole (21.23 ± 3.50 mm) and at end-diastole (33.50 ± 4.12 mm) were found to be significantly higher (P < .001) compared to control group values (left ventricular internal dimension at end-systole [LVIDs]; 17.46 ± 2.85 mm, LVIDd; 27.16 ± 4.20 mm, respectively). A significantly positive correlation in the French Bulldog group was noted between body weight and M-mode measurements (EPSS, IVSd, IVSs, LVIDd, LVIDs, and LVPWd). French bulldogs had a greater systolic and diastolic left ventricular volume than the control group. As a result, values reported in this study could be used as specific reference ranges in French Bulldogs.

Electrocardiographic and echocardiographic evaluation in dogs with hypothyroidism before and after levothyroxine supplementation: A prospective controlled study

Background

Improvement in cardiac function has been demonstrated after thyroxine treatment in humans with hypothyroidism using the myocardial performance index (MPI). Cardiac changes after thyroxine supplementation are poorly documented in dogs with spontaneous hypothyroidism and comparison with clinically healthy dogs is lacking.

Objectives

To evaluate the electrical activity and mechanical function of the heart in dogs with primary hypothyroidism at baseline (T0) and after thyroxine supplementation (T60).

Animals

Forty client‐owned dogs with hypothyroidism and 20 clinically healthy dogs.

Methods

Prospective cohort study. Selected electrocardiographic and echocardiographic variables, including the MPI, were measured in all dogs at T0 and in 30 hypothyroid dogs at T60.

Results

Hypothyroid dogs had significantly decreased median or mean heart rate (HR), P wave amplitude, and R wave amplitude (P = .04, P = .002, and P = .003, respectively) and E‐point‐to‐septal separation normalized to body weight (EPSSn) and trans‐mitral E wave velocity (E max; P < .001 and P = .025, respectively) at T0 compared to control dogs. At T60, significantly increased median or mean HR, P wave amplitude, fractional shortening, and E max (P < .001, P = .004, P = .002, and P = .009, respectively) and significantly decreased left ventricular end‐diastolic volume index, and normalized systolic diameter and EPSSn (P = .03, P = .03, and P = .001, respectively) were found.

Conclusions and Clinical Importance

Hypothyroidism in dogs induces mild and reversible changes of electromechanical cardiac function. The MPI does not have clinical importance in identifying cardiac dysfunction in affected dogs.

Right Heart Function of Fetuses and Infants with Large Ventricular Septal Defect: A Longitudinal Case-Control Study

The objective of this study was to detect the effect of a large ventricular septal defect (VSD) on right ventricular function before and after birth. All consecutive children with large VSD who were born in our hospital between January 2013-February 2016 and followed up throughout early infancy, and who lacked malformations or chromosomal abnormalities, were identified by a retrospective review of the medical records and included in this retrospective longitudinal case-control study (n = 30). Thirty normal control cases with an equivalent gestational age and gender served as controls. Tricuspid annular plane systolic excursion (TAPSE), right ventricle (RV) Tei index, and tricuspid E/E _m were measured in the fetal, neonatal (day 1-28), and infant (day 29-70) periods. In all periods, the VSD and control groups did not differ in TAPSE values, but VSD associated with higher Tei indices and tricuspid E/E _m values (in the fetal period: VSD group RV Tei was 0.48 ± 0.12 and E/E _m was 11.84 ± 1.53, control group RV Tei was 0.42 ± 0.16 and E/E _m was 10.16 ± 1.61; in neonatal period: VSD group RV Tei was 0.41 ± 0.17 and E/E _m was 12.21 ± 1.59, control group RV Tei was 0.30 ± 0.13 and E/E _m was 7.20 ± 1.28; in the infant period: VSD group RV Tei was 0.39 ± 0.09 and E/E _m was 11.89 ± 2.80, control group RV Tei was 0.28 ± 0.12 and E/E _m was 5.26 ± 1.90, all p < 0.05). In the fetal and neonatal periods, TAPSE correlated negatively with Tei index and tricuspid E/E _m in both groups. However, in the infant period, only the control group exhibited correlations between TAPSE and Tei index or tricuspid E/E _m. Tei index correlated positively with tricuspid E/E _m in both groups in all three periods. The VSD group had smaller correlation coefficients than the control group. Large VSD may already start to impair RV diastolic and global function before birth. This impairment continued and increased after birth. These changes did not associate with obvious RV longitudinal systolic function impairment. Large VSD mainly affected RV function by decreasing diastolic function and myocardial performance.

Echocardiographic assessment of canine degenerative mitral valve disease

Degenerative mitral valve disease (MVD), the most common acquired heart disease in small-sized dogs, is characterized by valvular degeneration resulting in systolic mitral valve regurgitation (MR). Worsening of MR leads to several combined complications including cardiac remodeling, increased left ventricular filling pressure, pulmonary arterial hypertension, and myocardial dysfunction. Conventional two-dimensional, M-mode, and Doppler examination plays a critical role in the initial and longitudinal assessment of dogs affected by MVD, providing information on mitral valve anatomy, MR severity, left ventricular (LV) size and function, as well as cardiac and vascular pressures. Several standard echocardiographic variables have been shown to be related to clinical outcome. Some of these markers (e.g., left atrium to aorta ratio, regurgitation fraction, pulmonary arterial pressure) may also help in identifying asymptomatic MVD dogs at higher risk of early decompensation, which remains a major issue in practice. However, both afterload and preload are altered during the disease course. This represents a limitation of conventional techniques to accurately assess myocardial function, as most corresponding variables are load-dependent. Recent ultrasound techniques including tissue Doppler imaging, strain and strain rate imaging, and speckle tracking echocardiography, provide new parameters to assess regional and global myocardial performance (e.g., myocardial velocities and gradients, deformation and rate of deformation, and mechanical synchrony). As illustration, the authors present new data obtained from a population of 91 dogs (74 MVD dogs, 17 age-matched controls) using strain imaging, and showing a significant longitudinal systolic alteration at the latest MVD heart failure stage.

Comparison of Doppler Flow Tei-Indexes With Pulmonary Artery Thermodilution Measurement of Cardiac Output in an Experimental Porcine Model

The objective of our study was to compare Doppler echocardiography imaging with pulmonary artery thermodilution measurement during mechanical ventilation. Total 78 piglets (6 weeks old, average weight 24 kg, under general anesthesia) were divided into 4 groups under different cardiac loading conditions (at rest, with increased left ventricular afterload, with increased right ventricular preload, and with increased afterload of both heart ventricles). At 60 and 120 min the animals were examined by echocardiography and simultaneously pulmonary artery thermodilution was used to measure cardiac output. Tei-indexes data were compared with invasively monitored hemodynamic data and cardiac output values together with calculated vascular resistance indices. A total of 224 parallel measurements were obtained. Correlation was found between values of right Tei-index of myocardial performance and changes in right ventricular preload (p<0.05) and afterload (p<0.01). Significant correlation was also found between left index values and changes of left ventricular preload (p<0.001), afterload (p<0.001), stroke volume (p<0.01), and cardiac output (p<0.01). In conclusion, echocardiographic examination and determination of the global performance selectively for the right and left ventricle can be recommended as a suitable non-invasive supplement to the whole set of methods used for monitoring of circulation and cardiac performance.

Repeated bedside echocardiography in children with respiratory failure

BACKGROUND

The aim of this study was to verify the benefits and limitations of repeated bedside echocardiographic examinations in children during mechanical ventilation. For the purposes of this study, we selected the data of over a time period from 2006 to 2010.

METHODS

A total of 235 children, average age 3.21 (SD 1.32) years were included into the study and divided into etiopathogenic groups. High-risk groups comprised: Acute lung injury and acute respiratory distress syndrome (ALI/ARDS), return of spontaneous circulation after cardiopulmonary resuscitation (ROSC), bronchopulmonary dysplasia (BPD), cardiomyopathy (CMP) and cardiopulmonary disease (CPD). Transthoracic echocardiography was carried out during mechanical ventilation. The following data were collated for statistical evaluation: right and left ventricle myocardial performance indices (RV MPI; LV MPI), left ventricle shortening fraction (SF), cardiac output (CO), and the mitral valve ratio of peak velocity of early wave (E) to the peak velocity of active wave (A) as E/A ratio. The data was processed after a period of recovery, i.e. one hour after the introduction of invasive lines (time-1) and after 72 hours of comprehensive treatment (time-2). The overall development of parameters over time was compared within groups and between groups using the distribution-free Wilcoxons and two-way ANOVA tests.

RESULTS

A total of 870 echocardiographic examinations were performed. At time-1 higher average values of RV MPI (0.34, SD 0.01 vs. 0.21, SD 0.01; p < 0.001) were found in all groups compared with reference values. Left ventricular load in the high-risk groups was expressed by a higher LV MPI (0.39, SD 0.13 vs. 0.29, SD 0.02; p < 0.01) and lower E/A ratio (0.95, SD 0.36 vs. 1.36, SD 0.64; p < 0.001), SF (0.37, SD 0.11 vs. 0.47, SD 0.02; p < 0.01) and CO (1.95, SD 0.37 vs. 2.94, SD 1.03; p < 0.01). At time-2 RV MPI were lower (0.25, SD 0.02 vs. 0.34, SD 0.01; p < 0.001), but remained higher compared with reference values (0.25, SD 0.02 vs. 0.21, SD 0.01; p < 0.05). Other parameters in high-risk groups were improved, but remained insignificantly different compared with reference values.

CONCLUSION

Echocardiography complements standard monitoring of valuable information regarding cardiac load in real time. Chest excursion during mechanical ventilation does not reduce the quality of the acquired data.

Tei index (myocardial performance index) and cardiac biomarkers in dogs with parvoviral enteritis

Tei index (myocardial performance) and cardiac biomarkers were evaluated in dogs with parvoviral enteritis (PVE). Tei index was calculated as isovolumic contraction time plus isovolumic relaxation time divided by ejection time. Myocardial and skeletal muscle damages were assessed by serum levels of cardiac troponin I (cTnI), creatine (phospho) kinase, lactate dehydrogenase and aspartate aminotransferase. Serum magnesium level was also determined. According to treatment response, dogs were divided into the survivor (n=20) and non-survivor groups (n=23). Seven healthy dogs served as controls. The mean value of the Tei index was higher in non-survivors, compared with survivors (p<0.02) and healthy controls (p<0.01). Serum level of cTnI in non-survivors was higher than that of survivors and controls (p<0.05). Tei index showed the highest sensitivity and specificity to predict mortality. The findings of an elevated Tei index and an increase in serum cTnI are factors associated with a poor prognosis in cases of canine parvovirosis.

The relationship between invasive hemodynamic measurements and tissue Doppler-derived myocardial velocity and acceleration during isovolumic relaxation in healthy dogs

This study investigated the feasibility of using the values of tissue Doppler imaging (TDI)-derived myocardial velocity during isovolumic relaxation (V(IR)) and myocardial acceleration during isovolumic relaxation (ACC) obtained from the left ventricular (LV) free wall to evaluate LV relaxation in normal dogs. Seven dogs were anesthetized, and dobutamine or esmolol was infused at a rate of 5.0 and 10.0 mug/kg/min or 100 and 500 mug/kg/min, respectively, via a cephalic vein. The order of drug administration (dobutamine or esmolol) was assigned to each dog. Simultaneous pulsed-Doppler (PD) echocardiography, TDI and hemodynamic measurements were performed. Compared with the baseline values, dobutamine significantly increased dP/dt min, but significantly shortened tau (tau). Similarly, esmolol significantly decreased dP/dt min, but significantly prolonged tau. Compared with the baseline values, dobutamine significantly increased V(IR) and ACC, and esmolol significantly decreased V(IR) and ACC. Both dP/dt min and tau were significantly correlated with TDI-derived IVRT (r=-0.43 and 0.74), V(IR) (r=0.85 and -0.49) and ACC (r=0.84 and -0.52). These results indicate that the TDI-derived V(IR) and ACC values obtained from the LV free wall can potentially be used to assess LV relaxation in dogs.

An index of myocardial performance applied to the right ventricle of Boxers with arrhythmogenic right ventricular cardiomyopathy

OBJECTIVE

To use an index of myocardial performance (IMP) to assess right ventricular function in Boxers with arrhythmogenic right ventricular cardiomyopathy (ARVC).

ANIMALS

22 Boxers (12 Boxers with ARVC diagnosed by the detection of > or = 1,000 ventricular premature complexes (VPCs)/24 h and 10 Boxers with < or = 5 VPCs/24 h (control dogs). Procedures-Pulsed-wave Doppler recordings of tricuspid inflow and pulmonic outflow were acquired. Preejection period (PEP), ejection time (ET), PEP/ET, and IMP were determined for the right ventricle by use of data from separate cardiac cycles.

RESULTS

A significant difference was not identified between groups for right ventricular PEP, right ventricular ET, right ventricular PEP/ET, or right ventricular IMP. Right ventricular IMP was not significantly correlated with VPC number (r = 0.21) or VPC grade (r = -0.3) in Boxers with ARVC.

CONCLUSIONS AND CLINICAL RELEVANCE

Boxers with ARVC did not have significant differences in right ventricular IMP, compared with results for control Boxers. This would suggest that right ventricular dysfunction does not develop in Boxers with ARVC or that a more severe phenotype of the disease may be necessary for detection of dysfunction. Additional studies that use more sensitive techniques to evaluate myocardial function may be warranted.

Doppler myocardial performance index in assessment of ventricular function in children with single ventricles

BACKGROUND

Quantitative assessment of ventricular function in children with single ventricles is both difficult and subjective because of asymmetric ventricular geometry. The Doppler myocardial performance index (MPI) allows the assessment regardless of ventricular shape. This study was designed to evaluate the feasibility of MPI in assessing ventricular function in children with single ventricles before and after total cavopulmonary connection (TCPC).

METHODS

Subjects consisted of 161 pediatric patients with single ventricles and 80 normal children without heart disease. The maximum positive rate of ventricular pressure change (Max dp/dt) was obtained in 58 patients by cardiac catheterization. Sixty-eight children with single ventricles received TCPC. MPI was calculated from Doppler tracings of ventricular inflow and outflow, then MPI of single ventricles before and after surgery and normal heart were compared.

RESULTS

Normal MPI value was 0.30+/-0.08 in the left ventricle and 0.26+/-0.08 in the right ventricle. Compared to normal children, MPI was significantly higher in 161 children with single ventricles (0.54+/-0.11, P<0.001). MPI correlated inversely with Max (dp/dt) (r=-0.77, P<0.01), and was positively related to age (r=0.54, P<0.01) in patients with single ventricles. MPI did not differ significantly before and after surgery in 68 patients with single ventricles (0.55+/-0.21 vs 0.51+/-0.20, P>0.05). However, MPI in 48 patients of <6 years old decreased significantly (0.55+/-0.21 vs 0.48+/-0.18, P<0.05), suggesting improved ventricular function.

CONCLUSIONS

Compared to normal children, ventricular function is impaired in patients with single ventricles and may worsen with age. MPI provides an accurate method for assessing ventricular function in children with single ventricles before and after TCPC.

Effects of changes in loading conditions and heart rate on the myocardial performance index in cats

OBJECTIVE

To evaluate the effect of changes in hemodynamics on the myocardial performance index (MPI) in cats.

ANIMALS

6 mixed-breed cats.

PROCEDURES

Cats were anesthetized by administration of thiopental sodium; anesthesia was maintained by administration of isoflurane. Systolic arterial pressure and central venous pressure were measured by use of catheters, and heart rate was controlled by right atrial pacing. Afterload was increased by balloon occlusion of the descending aorta, and preload was increased by IV infusion of lactated Ringer's solution at a rate of 40 mL/kg/h. Echocardiography was performed for each condition.

RESULTS

Atrial pacing significantly increased heart rate. The MPI did not change with heart rate. Arterial pressure and MPI increased significantly during aortic occlusion. The IV infusion increased fractional shortening but did not change the MPI. Multiple regression analysis revealed that the MPI was not affected by heart rate, systolic arterial pressure, central venous pressure, fractional shortening, or velocity of the E wave.

CONCLUSIONS AND CLINICAL RELEVANCE

The MPI can be used to assess cardiac function in healthy cats. The MPI is independent of heart rate and systolic arterial pressure but is sensitive to changes in afterload.