Objective—To assess the agreement between cardiac output (CO) measured by use of arterial pressure waveform analysis (PulseCO) and lithium dilution (LiDCO) in conscious dogs with systemic inflammatory response syndrome (SIRS).
Animals—14 dogs with naturally occurring SIRS.
Procedures—Pulse power analysis was performed on critically ill patients with a PulseCO monitor. All measurements were obtained with an indwelling arterial line and in accordance with the manufacturer's instructions. Intermittent measurements of CO were obtained with the LiDCO method to validate the PulseCO measurements at initial calibration (baseline; time 0) and at 4, 8, 16, and 24 hours. The 2 methods for measuring CO were compared by use of Bland-Altman analysis. An error rate for the limits of agreement between the 2 methods of < 30% was defined as being acceptable.
Results—Bland-Altman analysis did not indicate good agreement between measurements obtained by use of the PulseCO and LiDCO methods, despite no significant change in cardiac index (CI) over time as measured with the LiDCO method. The percentage error for the overall difference in CI values between the PulseCO and LiDCO measurements was 122%, which indicated that the PulseCO method was not an acceptable means of CO measurement when compared with the LiDCO method for this patient population.
Conclusions and Clinical Relevance—Agreement between the PulseCO and LiDCO methods for measurement of CO was not acceptable at 4- and 8-hour intervals after calibration in conscious dogs with naturally occurring SIRS.
Objective—To characterize the cardiopulmonary effects of dobutamine and norepinephrine infusion in isoflurane-anesthetized healthy alpacas.
Animals—8 adult alpacas.
Procedures—Initial baseline cardiovascular, respiratory, and metabolic variables were obtained 30 minutes after induction of isoflurane anesthesia in 8 alpacas (3 females and 5 sexually intact males). Four treatments (dobutamine at 4 and 8 μg/kg/min and norepinephrine at 0.3 and 1 μg/kg/min) were administered in random order via constant rate infusion over 15 minutes, followed by repeat measurements of cardiopulmonary values and a 20-minute washout period. Subsequent baseline and posttreatment measurements were similarly repeated until both drugs and dosages were administered to each animal. Baseline data in awake alpacas were obtained 18 to 24 hours following recovery from anesthesia.
Results—Both dobutamine and norepinephrine significantly increased cardiac index and arterial blood pressure from baseline values. Similar increases in hemoglobin concentration, oxygen content, and oxygen delivery were observed following administration of each drug at either dosage. Only dobutamine, however, reduced relative oxygen consumption while improving overall tissue oxygenation. Furthermore, heart rate was selectively enhanced by dobutamine and systemic vascular resistance by norepinephrine. Norepinephrine infusion resulted in dose-dependent changes in cardiopulmonary variables.
Conclusions and Clinical Relevance—Results indicated that both dobutamine and norepinephrine were appropriate choices to improve cardiac index, mean arterial pressure, and overall oxygen delivery in alpacas with isoflurane-induced hypotension. Careful titration by use of low infusion rates of dobutamine and norepinephrine is recommended to avoid potential arrhythmogenic effects and excessive vasoconstriction, respectively.
Objective—To evaluate the accuracy of a commercial ultrasonographic cardiac output (CO) monitoring system (UCOMS) in anesthetized Beagles as assessed by comparison with thermodilution CO (TDCO).
Animals—8 healthy anesthetized Beagles.
Procedures—Simultaneous UCOMS and TDCO measurements of CO were obtained during 4 hemodynamic states: baseline anesthesia (0.5% to 1.5% isoflurane), a higher depth of anesthesia (2% to 3.5% isoflurane) to yield a ≥ 15% reduction in systolic arterial blood pressure, IV infusion of colloidal solution to a mean right atrial pressure of ≥ 15 mm Hg, and IV infusion of dobutamine at 5 μg/kg/min. Measurements were obtained at 2 probe positions: the subxiphoid region and the right thoracic inlet. Correlation and agreement of results between methods were determined via linear regression analysis and Bland-Altman plots.
Results—A significant positive correlation was detected between UCOMS andTDCO measurements obtained at the subxiphoid (R = 0.86) and thoracic inlet (R = 0.83) positions. Bland-Altman plots revealed minimal bias between methods (bias ± SD, −0.03 ± 0.73 L/min and −0.20 ± 0.80 L/min for subxiphoid and thoracic inlet measurements, respectively). However, the percentage error associated with UCOMS measurements made at the 2 positions was > 45%.
Conclusions and Clinical Relevance—When compared with the results of TDCO, CO measured with the UCOMS exceeded commonly accepted limits of error in healthy dogs. The UCOMS was, however, able to track changes in CO across hemodynamic states. Additional research is needed to assess the usefulness of the UCOMS for monitoring CO in critically ill dogs.
Objective—To evaluate serum cardiac biomarker concentrations and selected enzyme activities in dogs with experimentally induced bradyarrhythmias after short- (1-hour) and long- (3-hour) duration transcutaneous cardiac pacing (TCP).
Animals—10 healthy Beagles.
Procedures—In each dog, anesthesia was induced with propofol (5 mg/kg, IV) and maintained via inhalation of isoflurane in oxygen. To induce bradyarrhythmia, diltiazem was administered IV (20 to 50 mg/dog). Transcutaneous cardiac pacing was performed for 1 hour (5 dogs) or 3 hours (5 dogs) by use of an automated external cardiac pulse generator and a transdermal electrode. Serum concentrations of creatine kinase-MB fraction and cardiac troponin I and activities of aspartate transaminase, creatine kinase, and lactate dehydrogenase were evaluated the day before (baseline) and at intervals until 7 days after TCP.
Results—Increases (from baseline) in serum cardiac biomarker concentrations and enzyme activities were detected in the long-duration TCP group; changes in the short-duration TCP group were more minor and largely not significant. Although severity of myocardial and skeletal muscular injuries was apparently greater with greater duration of TCP, the injuries were not persistent; most variables were within reference range within 3 days after TCP.
Conclusions and Clinical Relevance—Results indicated that application of TCP for > 1 hour in dogs may cause myocardial and skeletal muscular injuries. Serum concentrations of creatine kinase-MB fraction and cardiac troponin I and activities of aspartate transaminase, creatine kinase, and lactate dehydrogenase should be more carefully monitored after TCP of > 1 hour's duration to evaluate potential myocardial damages.
Objective—To investigate use of signal analysis of heart sounds and murmurs in assessing severity of mitral valve regurgitation (mitral regurgitation [MR]) in dogs with myxomatous mitral valve disease (MMVD).
Animals—77 client-owned dogs.
Procedures—Cardiac sounds were recorded from dogs evaluated by use of auscultatory and echocardiographic classification systems. Signal analysis techniques were developed to extract 7 sound variables (first frequency peak, murmur energy ratio, murmur duration > 200 Hz, sample entropy and first minimum of the auto mutual information function of the murmurs, and energy ratios of the first heart sound [S1] and second heart sound [S2]).
Results—Significant associations were detected between severity of MR and all sound variables, except the energy ratio of S1. An increase in severity of MR resulted in greater contribution of higher frequencies, increased signal irregularity, and decreased energy ratio of S2. The optimal combination of variables for distinguishing dogs with high-intensity murmurs from other dogs was energy ratio of S2 and murmur duration > 200 Hz (sensitivity, 79%; specificity, 71%) by use of the auscultatory classification. By use of the echocardiographic classification, corresponding variables were auto mutual information, first frequency peak, and energy ratio of S2 (sensitivity, 88%; specificity, 82%).
Conclusions and Clinical Relevance—Most of the investigated sound variables were significantly associated with severity of MR, which indicated a powerful diagnostic potential for monitoring MMVD. Signal analysis techniques could be valuable for clinicians when performing risk assessment or determining whether special care and more extensive examinations are required.
Objective—To report reference values and examine the agreement in the myocardial performance (Tei) index of the left ventricle (LVTI) as measured by tissue Doppler imaging (TDI), pulsed-wave Doppler imaging (PWD), and M-mode echocardiography in clinically normal rabbits.
Animals—26 clinically normal male New Zealand White rabbits.
Procedures—Echocardiographic examinations that included TDI, PWD, and M-mode echocardiography were performed. Rabbits were sedated by SC administration of ketamine and midazolam. Intraclass correlation coefficients (ICCs) were used to measure absolute agreement among the 3 echocardiographic techniques. Intraclass correlation coefficients were computed for values a and b and for the equation (a – b)/b used to determine LVTI; value a equals the sum of isovolumic contraction time, ejection time, and isovolumic relaxation time, and value b equals the left ventricular ejection time. Values of ICC > 0.75 indicated good agreement between 2 echocardiographic techniques.
Results—For value a, Pearson correlation coefficients between pairs of techniques were all high (r r 0.7). However, only the septal TDI and the lateral wall TDI had good agreement (ICC, 0.86). For value b, correlations were generally low with the exception of the correlation between the septal and the lateral wall TDI. For value b, TDI was the only technique with good agreement (ICC, 0.77). For LVTI, only TDI techniques had a significantly positive correlation. All the other correlations were close to zero with a paradoxic moderate negative correlation between PWD-determined LVTI and lateral wall TDI–determined LVTI.
Conclusions and Clinical Relevance—For LVTI, the absolute agreement was poor between all pairs of techniques.
Objective—To compare the acute effects of cardiac pacing from various transvenous pacing sites on left ventricular (LV) function and synchrony in clinically normal dogs.
Animals—10 healthy adult mixed-breed dogs.
Procedures—Dogs were anesthetized, and dual-chamber transvenous biventricular pacing systems were implanted. Dogs were paced in single-chamber mode from the right atrial appendage (RAA) alone and in dual-chamber mode from the right ventricular apex (RVA), from the left ventricular free wall (LVFW), and simultaneously from the RVA and LVFW (BiV). Standard ECG and echocardiographic measurements, cardiac output measured with the lithium dilution method (LiDCO), and tissue Doppler–derived measurements of LV synchrony were obtained during each of the pacing configurations.
Results—Placement of the biventricular pacing systems was possible in 8 of the 10 dogs. The QRS duration was significantly different among all pacing sites, and the order of increasing duration was RAA, BiV, LVFW, and RVA. Pacing sites did not differ with respect to fractional shortening; however, pacing from the RVA resulted in a significantly lower ejection fraction than pacing from all other sites. During RVA and LVFW pacing, LiDCO was significantly lower than that at other sites; there was no significant difference between RAA and BiV pacing with respect to LiDCO. Although the degree of dyssynchrony was significantly lower during pacing from the RAA versus other ventricular pacing sites, it was not significantly different among sites.
Conclusions and Clinical Relevance—Ventricular activation by RAA pacing provided the best LV function and synchrony. Pacing from the RVA worsened LV function, and although pacing from the LVFW improved it, BiV pacing may provide additional improvement.
Procedures—Systolic intervals and indices of myocardial contractility of the left ventricle were measured in conscious sheep by use of polycardiography.
Results—The mean ± SD pre-ejection period was 59 ± 12 milliseconds, and the mean left ventricular ejection time was 194 ± 34 milliseconds. The mean myocardial tension index was 0.22 ± 0.05, and the mean ratio of the pre-ejection period to ejection time was 0.30 ± 0.09. Total electromechanical systole, mechanical systole, and ejection time varied inversely with heart rate. The electromechanical delay and pre-ejection period were not correlated with heart rate, nor were the myocardial tension index and the ratio of the pre-ejection period to ejection time. The isovolumetric contraction index and isovolumetric contraction time were not significantly correlated with heart rate, although the values for the correlation coefficient were moderate (r = −0.561 and r = −0.482, respectively).
Conclusions and Clinical Relevance—Although a larger study would be needed to provide reference intervals for healthy sheep, the results of the study reported here provided useful information for the cardiac evaluation of sheep.
Objective—To compare cardiac output (CO) measured by lithium arterial pressure waveform analysis (PULSECO) and CO measured by transpulmonary pulse contour analysis (PICCO) in anesthetized foals, with CO measured by use of lithium dilution (LIDCO) considered the criterion-referenced standard.
Sample Population—6 neonatal (1- to 4-day-old) foals that weighed 38 to 45 kg.
Procedures—Foals were anesthetized and instrumented to measure direct blood pressure, heart rate, arterial blood gases, and CO. The CO was measured by use of PULSECO, PICCO, and LIDCO techniques. Measurements were converted to specific CO (sCO) values for statistical analysis. Measurements were obtained during low, intermediate, and high CO states.
Results—sCO ranged from 75.5 to 310 mL/kg/min. Mean ± SD PICCO bias varied significantly among CO states and was −51.9 ± 23.1 mL/kg/min, 20.0 ± 19.5 mL/kg/min, and 87.2 ± 19.5 mL/kg/min at low, intermediate, and high CO states, respectively. Mean PULSECO bias (11.0 ± 37.5 mL/kg/min) was significantly lower than that of PICCO and did not vary among CO states. Concordance correlation coefficient between LIDCO and PULSECO was significantly greater than that between LIDCO and PICCO. The proportion of observations with a relative bias < ± 30% was significantly lower with the PULSECO method than with the PICCO method.
Conclusions and Clinical Relevance—Values for the PULSECO method were more reproducible and agreed better with values for the LIDCO method than did values for the PICCO method and were able to more accurately monitor changes in CO in anesthetized newborn foals.
Objective—To determine whether plasma N-terminal proatrial natriuretic peptide (Nt-proANP) concentrations in cats with cardiomyopathy (CM) differ from values in healthy cats and evaluate whether plasma Nt-proANP concentrations can be used to discriminate cats with CM and congestive heart failure (CHF) from CM-affected cats without CHF.
Animals—16 cats that had CM without CHF, 16 cats that had CM with CHF, and 11 healthy control cats.
Procedures—All cats underwent a physical examination, assessment of clinicopathologic variables (including plasma thyroxine concentration), thoracic radiography, and echocardiography. On the basis of findings, cats were assigned to 1 of 3 groups (control cats, cats with CM and CHF, and cats with CM without CHF). Venous blood samples were obtained from all 43 cats, and plasma Nt-proANP concentrations were measured by use of a human proANP(1-98) ELISA.
Results—Plasma Nt-proANP concentrations differed significantly among the 3 groups. Median Nt-proANP concentration was 381 fmol/mL (range, 52 to 450 fmol/mL), 763 fmol/mL (range, 167 to 2,386 fmol/mL), and 2,443 fmol/mL (range, 1,189 to 15,462 fmol/mL) in the control group, in cats with CM without CHF, and in cats with CM and CHF, respectively.
Conclusions and Clinical Relevance—Measurement of plasma Nt-proANP concentration could be of benefit in the assessment of cats with naturally occurring CM and might have potential as a screening marker for the disease. Furthermore, measurement of plasma NtproANP concentration may be useful for distinguishing cats with CM and CHF from those with CM and no CHF.