Papillary muscle measurements in cats with normal echocardiograms and cats with concentric left ventricular hypertrophy

BACKGROUND: Papillary muscle hypertrophy can occur in conjunction with, or as the only indication of, hypertrophic cardiomyopathy or other diseases that result in left ventricular concentric hypertrophy (LVCH). Assessment of papillary muscle size is usually subjective because objective measures have not been reported. HYPOTHESIS: The study hypothesis was that papillary muscle dimensions are different between normal cats and cats with LVCH. ANIMALS: Echocardiograms from 44 normal cats and 40 cats with LVCH were included in the study. METHODS: All measurements were taken from the right parasternal short-axis view at the level of the papillary muscles at end-diastole. Three methods were used to assess papillary muscle size: the area subtraction method, the direct area trace method, and the diameter method. Measurements were compared between cat groups and method comparisons were made among methods for area determination. RESULTS: Cats with LVCH were older and had significantly greater left ventricular septal and free wall thicknesses and larger left atrial measurements than normal cats (P < .0006). Papillary muscle measurements were significantly greater by all measurement methods in cats with LVCH than in cats with normal echocardiograms (P < .0001). The area subtraction method and direct area trace method showed moderate agreement. CONCLUSIONS AND CLINICAL IMPORTANCE: Papillary muscle measurements were larger for LVCH cats than normal cats; however, some overlap was present. The establishment of these objective measures adds to the echocardiographic examination of cats.     

Diagnostic and prognostic utility of surface electrocardiography in cats with left ventricular hypertrophy

Objectives

To assess the ability of electrocardiography (ECG) to predict left ventricular hypertrophy (LVH) in the cat and to investigate the prognostic value of selected ECG variables in cats with LVH.

Assessment of hypertension in 40 cats with left ventricular hypertrophy by Doppler-shift sphygmomanometry

Forty cats with left ventricular hypertrophic disease had blood pressure evaluated indirectly by Doppler-shift sphygmomanometry. Disease categories included hyperthyroidism, chronic renal insufficiency and hypertrophic cardiomyopathy unrelated to either of the first two disorders. Nineteen (47-5 per cent) of the 40 cats had systemic hypertension, nine had high systolic blood pressure only, 10 had high systolic and diastolic blood pressure, and none had only isolated diastolic hypertension. Blood pressure did not correlate with the degree of left ventricular thickness. The results of this study suggest a high prevalence of both left ventricular hypertrophy and systemic hypertension. Cause and effect relationships require further evaluation.     

Effects of sedation on echocardiographic variables of left atrial and left ventricular function in healthy cats

Although sedation is frequently used to facilitate patient compliance in feline echocardiography, the effects of sedative drugs on echocardiographic variables have been poorly documented. This study investigated the effects of two sedation protocols on echocardiographic indices in healthy cats, with special emphasis on the assessment of left atrial size and function, as well as left ventricular diastolic performance. Seven cats underwent echocardiography (transthoracic two-dimensional, spectral Doppler, color flow Doppler and tissue Doppler imaging) before and after sedation with both acepromazine (0.1 mg/kg IM) and butorphanol (0.25 mg/kg IM), or acepromazine (0.1 mg/kg IM), butorphanol (0.25 mg/kg IM) and ketamine (1.5 mg/kg IV). Heart rate increased significantly following acepromazine/butorphanol/ketamine (mean ± SD of increase, 40 ± 26 beats/min) and non-invasive systolic blood pressure decreased significantly following acepromazine/butorphanol (mean ± SD of decrease, 12 ± 19 mmHg). The majority of echocardiographic variables were not significantly different after sedation compared with baseline values. Both sedation protocols resulted in mildly decreased left ventricular end-diastolic dimension and mildly increased left ventricular end-diastolic wall thickness. This study therefore failed to demonstrate clinically meaningful effects of these sedation protocols on echocardiographic measurements, suggesting that sedation with acepromazine, butorphanol and/or ketamine can be used to facilitate echocardiography in healthy cats.     

Non-invasive assessment of left ventricular relaxation property using color M-mode-derived intraventricular pressure gradients in cats

IntroductionDiastolic dysfunction is an early clinical feature of feline hypertrophic cardiomyopathy (HCM). The left ventricular filling in early diastole is facilitated by the diastolic intraventricular pressure gradient (IVPG). The study objectives were to evaluate color Doppler M-mode-derived IVPG calculation in cats as a non-invasive assessment of the left ventricular relaxation property to determine the normal ranges of peak IVPG in cats and investigate the influence of left ventricular function and heart rate (HR).AnimalsOne hundred and six client-owned apparently healthy cats.MethodsProspective cross-sectional study. Quantitative analysis of color Doppler M-mode images was used to estimate total and segmental IVPGs non-invasively.ResultsThe total IVPG was 0.76 mmHg (95% reference interval (RI): 0.28–1.29 mmHg), the basal IVPG 0.34 mmHg (95% RI: 0.07–0.63 mmHg), and the mid-apical IVPG 0.42 mmHg (95% RI: 0.15–0.71 mmHg). Total and segmental IVPG increased with HR (P < 0.003), while segmental percent IVPG was HR independent. A short isovolumic relaxation time (IVRT) and a high mitral annular velocity in early diastole were associated with an increase in total IVPG (P = 0.008 and P = 0.009, respectively) adjusted for HR. An increase in IVPG was associated with an increase in mitral inflow velocity (P < 0.001).ConclusionsFeline IVPGs increase with HR and a short IVRT, which was believed to be a normal physiologic adrenergic response associated with an increased sympathetic tone. Future studies of segmental IVPG changes in feline HCM are needed to evaluate the clinical applicability of color Doppler M-mode estimated IVPGs in feline cardiology.     

The effect of atenolol on NT-proBNP and troponin in asymptomatic cats with severe left ventricular hypertrophy because of hypertrophic cardiomyopathy: a pilot study

Background: Atenolol often is used empirically in cats with hypertrophic cardiomyopathy (HCM) before the onset of heart failure, although evidence of efficacy is lacking. Cardiac biomarkers play a critical role in the early detection of subclinical cardiac disease, in the prediction of long‐term prognosis, and in monitoring the response to therapy in humans. Hypothesis: Circulating concentrations of the biomarkers N‐terminal pro‐B type natriuretic peptide (NT‐proBNP) and cardiac troponin I (cTnI) will decrease after chronic administration of atenolol PO to cats with severe HCM but no signs of heart failure. Animals: Six Maine Coon or Maine Coon cross cats with severe HCM. Methods: Cats were treated with atenolol (12.5 mg PO q12 h) for 30 days. No cat had left ventricular dynamic outflow tract obstruction caused by systolic anterior motion of the mitral valve. The concentrations of NT‐proBNP and cTnI were assayed before and on the last day of drug administration. Results: There was no statistically significant change in NT‐proBNP (median before, 394 pmol/L; range, 71–1,500 pmol/L; median after, 439 pmol/L; range, 24–1,500 pmol/L; P = .63) or in cTnI (median before, 0.24 ng/mL; range, 0.10–0.97 ng/mL; median after, 0.28 ng/mL; range, 0.09–1.0 ng/mL; P = .69) after administration of atenolol. Conclusions: Atenolol administration did not decrease NT‐proBNP or cTnI concentrations in cats with severe left ventricular hypertrophy caused by hypertrophic cardiomyopathy. These results suggest that atenolol did not decrease myocardial ischemia and myocyte death in these cats. A larger clinical trial is warranted to verify these findings.     

Quantification of left ventricular diastolic wall motion by Doppler tissue imaging in healthy cats and cats with cardiomyopathy

OBJECTIVE: To assess Doppler tissue imaging (DTI) for evaluating left ventricular diastolic wall motion in healthy cats and cats with cardiomyopathy. ANIMALS: 20 healthy cats, 9 cats with hypertrophic cardiomyopathy (HCM), and 9 cats with unclassified cardiomyopathy (UCM). PROCEDURE: A pulsed wave DTI sample gate was positioned at a subendocardial region of the left ventricular free wall in the short axis view and at the lateral mitral annulus in the apical 4-chamber view. Indices of diastolic wall motion were measured, including peak diastolic velocity (PDV), mean rate of acceleration and deceleration of the maximal diastolic waveform (MDWaccel and MDWdecel, respectively), and isovolumetric relaxation time (IVRT). RESULTS: The PDV of cats with HCM and 6 of 9 cats with UCM was significantly decreased, compared with that of healthy cats. In the 3 cats with UCM that had a PDV that was not different from healthy cats, MDWaccel and MDWdecel were greater, and IVRT was shorter than those of healthy cats. The IVRT in cats with HCM was longer than that of other cats. CONCLUSIONS AND CLINICAL RELEVANCE: Indices of diastolic function in cats with HCM, and in many cats with UCM, differed from those of healthy cats and were similar to those reported in humans with HCM and restrictive cardiomyopathy, respectively. However, the hemodynamic abnormality was not the same for all cats with UCM; some cats with an enlarged left atrium and a normal left ventricle (ie, UCM) had abnormal left ventricular wall motion consistent with restrictive cardiomyopathy while others did not.     

Effects of vagal maneuvers on heart rate and Doppler variables of left ventricular filling in healthy cats

BackgroundEvaluation of left ventricular (LV) diastole is clinically important in cats with heart disease. Diastolic dysfunction is a main characteristic of feline cardiomyopathy and is associated with clinical signs and poor outcome. Numerous echocardiographic indices characterizing LV diastole exist, of which Doppler variables of transmitral flow and mitral annular motion are used most often. However, rapid heart rate (HR), a common finding in cats examined in the veterinary hospital environment, may cause summation of flow waves limiting interpretation of diastolic function.ObjectiveTo evaluate the effects of vagal maneuvers (gentle eyeball pressure and nasal planum massage) on HR and Doppler variables of LV diastolic filling.AnimalsTwenty-four healthy client-owned cats with summated transmitral flow waves at baseline.MethodsProspective observational study. Transthoracic echocardiography was performed and Doppler transmitral and mitral annular tissue Doppler velocities recorded both before and during vagal maneuvers. Data were compared using a paired t-test.ResultsApplication of vagal maneuvers temporarily decreased HR in all cats (mean reduction ± SD; 42 ± 22 bpm). The duration of HR reduction (<5 s, 5–10 s, and >10–15 s) was evenly distributed among groups (8 cats in each). Summated Doppler transmitral flow and mitral annular tissue velocity waves were separated during vagal maneuvers in 71% and 72% of cats, respectively. No adverse effects were observed.ConclusionsVagal maneuvers may be utilized as a simple non-pharmacologic tool in the Doppler evaluation of LV diastolic function in healthy cats.     

Pulsed Doppler assessment of left ventricular diastolic function in normal and cardiomyopathic cats.

Left ventricular (LV) diastolic function was evaluated in 16 cats with primary hypertrophic cardiomyopathy (HCM) using pulsed Doppler (PD) assessment of transmitral flow and isovolumic relaxation time. Data obtained was compared to data from 12 healthy, adult, research cats. Compared to normal cats, the HCM group showed significantly (p value less than 0.05) reduced early LV inflow velocities (mean +/- standard error [SE], peak velocity of 0.70+/-0.04 m/s versus 0.54+/-0.04 m/s and integrated velocity of 0.48+/-0.08 m/s versus 0.37+/-0.03 m/s); a reduced rate of deceleration of early inflow (mean+/-SE, -12.0+/-1.0 m/s2 versus -5.1+/-1.1 m/s2); prolonged isovolumic relaxation time (mean +/- SE, 45.7+/-3.3 ms versus 76.0+/-3.1 ms); and increased atrial systolic flow velocities (mean +/- SE, peak velocity of 0.29+/-0.04 m/s versus 0.48+/-0.04 m/s and integrated velocity of 0.21+/-0.03 m/s versus 0.34+/-0.03 m/s). The results suggest that PD provides a noninvasive method of identifying and quantifying functional diastolic impairment in cats with HCM.     

Dose-dependent inhibition of angiotensin converting enzyme by enalapril in cats

Although heart failure in cats is treated with angiotensin converting enzyme (ACE) inhibitors, data on the effects of different doses of enalapril on hemodynamics and the inhibition of ACE activity have not been published. To evaluate the effect of enalapril, 0.25, 0.5, or 1.0 mg/kg was given once (s.i.d., p.o.) or twice (b.i.d., p.o.) a day, and plasma ACE activity, indirect blood pressure, and heart rate were measured. Plasma ACE activity and blood pressure fell dose-dependently. There was a biphasic effect on blood pressure with twice daily administration. Enalapril 0.25 mg/kg b.i.d. inhibited plasma ACE activity by 40% after 24 hr, which was almost the same as the effect of 0.5 and 1.0 mg/kg s.i.d., and 0.5 and 1.0 mg/kg b.i.d., while 0.25 mg/kg s.i.d. inhibited it by 23%. Thus, enalapril with a daily dose exceeding 0.5 mg/kg may provide similar efficacy of ACE inhibition in cats.     

Doppler echocardiographic effects of medetomidine on dynamic left ventricular outflow tract obstruction in cats

OBJECTIVE: To evaluate the effects of medetomidine on dynamic left ventricular outflow tract (LVOT) obstruction in cats with left ventricular hypertrophy. DESIGN: Clinical trial. ANIMALS: 6 domestic shorthair cats with echocardiographic evidence of dynamic LVOT obstruction. PROCEDURE: Cats were restrained in lateral recumbency, and baseline M-mode and Doppler echocardiographic examinations were performed. An ECG was recorded continuously, and blood pressure was measured indirectly with Doppler instrumentation. Medetomidine (20 microg/kg 19.1 microg/lb]) was then administered i.m., and examinations were repeated 15 minutes later. RESULTS: Significant decreases in heart rate, LVOT velocity, and the LVOT pressure gradient were documented following medetomidine administration. After adjusting for the effects of heart rate by ANCOVA, there were no significant differences in any other systolic or diastolic indices of left ventricular function. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that administration of medetomidine to cats with dynamic LVOT obstruction may result in elimination of outflow tract obstruction; medetomidine may be a suitable sedative and analgesic agent in this subpopulation of cats.     

Effect of enalapril on blood pressure, renal function, and the renin-angiotensin-aldosterone system in cats with autosomal dominant polycystic kidney disease

OBJECTIVE: To evaluate blood pressure, renal function, and the renin-angiotensin-aldosterone system (RAAS) in cats with autosomal dominant polycystic kidney disease (ADPKD) and to assess the effect of enalapril on these variables. ANIMALS: 6 cats with ADPKD and 6 age-matched healthy cats. PROCEDURE: To measure blood pressure and heart rate, a radiotelemetry catheter was placed in the left femoral artery of each cat. Baseline data collection included 24-hour blood pressure, heart rate, and motor activity. Blood was then collected for analysis of RAAS status and renal function. Enalapril (0.5 mg/kg of body weight, p.o., q 24 h) was administered for 1 week, and data collection was repeated. RESULTS: Differences in baseline blood pressure, heart rate, motor activity, RAAS status, and renal function were not detected between cats with ADPKD and control cats. Hypertension was not documented in cats with ADPKD. Blood pressure was significantly reduced for 15 to 17 hours after treatment with enalapril in both groups. Administration of enalapril also resulted in significant increases in plasma renin activity and significant decreases in angiotensin converting enzyme activity and atrial natriuretic peptide concentration but only minimal changes in glomerular filtration rate and effective renal plasma flow in both groups of cats. CONCLUSIONS AND CLINICAL RELEVANCE: Although hypertension is common in humans with ADPKD, cats with ADPKD were normotensive. Treatment with enalapril (0.5 mg/kg, p.o., q 24 h) significantly reduced blood pressure in normotensive healthy cats and cats with ADPKD, and resulted in predictable changes in RAAS enzyme activities and hormone concentrations. Enalapril had minimal effects on renal function.     

Effect of spironolactone on diastolic function and left ventricular mass in Maine Coon cats with familial hypertrophic cardiomyopathy

BACKGROUND: Myocardial fibrosis occurs in cats with hypertrophic cardiomyopathy (HCM), and is one factor that leads to diastolic dysfunction. Spironolactone (SPIR) reduces myocardial fibrosis in several models of HCM and in humans with cardiac disease. HYPOTHESIS: SPIR will improve diastolic function and reduce left ventricular (LV) mass in Maine Coon cats with HCM. METHODS: Maine Coon cats with familial HCM were included if there was concentric hypertrophy (> or =6 mm end diastolic wall thickness) and decreased early lateral mitral annular velocity (Em) or summated early and late mitral annular velocity (EAsum) measured by pulsed wave tissue Doppler imaging echocardiography. Cats were paired by Em-EAsum and randomized to receive 2 mg/kg SPIR (n = 13) or placebo (n = 13) PO q12 h for 4 months. Em-EAsum, systolic velocity, LV mass, and the ratio of left atrial to aortic diameter were measured at baseline, 2 months, and 4 months. Statistical analysis included 2-way repeated measures analysis of variance and the Student's t-test. RESULTS: Plasma aldosterone concentration increased in cats treated with SPIR (235 ng/mL, baseline; 935 ng/mL, 2 months; 1,077 ng/mL, 4 months; P < .001 at 2 and 4 months). No significant treatment effect was identified for early or early-late summated diastolic mitral annular velocity or any other variable except plasma aldosterone concentration. Severe facial ulcerative dermatitis developed in 4 of 13 cats treated with SPIR, requiring discontinuation of the drug. CONCLUSION: SPIR did not improve Em or EAsum of the lateral mitral annulus or alter LV mass over 4 months. One third of cats treated with SPIR developed severe ulcerative facial dermatitis.     

Blood pressure assessment in healthy cats and cats with hypertensive retinopathy

OBJECTIVE: To determine whether there was an association between hypertensive retinopathy and high systolic, diastolic, and mean arterial blood pressures in cats. ANIMALS: 181 cats. PROCEDURE: Systolic, diastolic, and mean arterial blood pressures were measured by use of a noninvasive oscillometric technique. The range of blood pressure measurements in healthy cats from various age groups was determined. Associations among systolic, diastolic, and mean arterial blood pressure; hypertensive retinopathy; hyperthyroidism; left ventricular cardiac hypertrophy; chronic renal failure; and serum biochemical abnormalities were determined. RESULTS: All blood pressure measurements increased with age in healthy cats. The frequency of hypertensive retinopathy also increased with age and with blood pressure, and hypertensive retinopathy was particularly found in cats with systolic blood pressures > 168 mm Hg. There was an increased risk for hypertensive retinopathy in cats that were female, > 10 years old, and neutered. The risk of chronic renal failure also increased as blood pressure, particularly systolic blood pressure, increased. CONCLUSIONS AND CLINICAL RELEVANCE: Hypertensive retinopathy was common in cats > or = 10 years of age and was associated with systolic blood pressures > 168 mm Hg when measured by the noninvasive oscillometric technique.     

Estimation of left ventricular filling pressure by Doppler echocardiography in dogs with pacing-induced heart failure

BACKGROUND: Congestive heart failure (CHF) is a common clinical syndrome characterized by elevated filling pressure. HYPOTHESIS: Doppler echocardiographic (DE) variables of left ventricular (LV) filling can predict a decline of LV end-diastolic pressure (LVEDP) induced by acute preload reduction in dogs with compensated CHF. ANIMALS: Five male hound dogs. METHODS: Dogs previously instrumented with a transvenous cardiac pacemaker and a LV pressure gauge were paced at 160-180 bpm to induce mild CHF characterized by LVEDP > 20 mmHg. LVEDP and 9 DE variables of LV filling derived from diastolic time intervals, transmitral and pulmonary venous flow, and tissue Doppler imaging were measured simultaneously at baseline and 30, 60, 120, and 240 minutes after furosemide (4 mg/kg, IV) or placebo (0.9% saline, IV). Repeated measures analysis of variance and correlation analysis were used to determine the association between the decline of LVEDP after furosemide and DE measures of LV filling pressure (LVFP). RESULTS: Furosemide but not placebo decreased LVEDP (P < .001). The ratio of early transmitral flow velocity to LV isovolumic relaxation time (E : IVRT) predicted LVEDP best (R(2)= .50; P < .001). Correlations were also found between LVEDP and IVRT, E, ratio between E and late diastolic transmitral flow velocity (E : A), and early diastolic velocity of the mitral annulus (Ea). The ratio of E to Ea (E : Ea) was not useful in the prediction of LVEDP in this model. CONCLUSION AND CLINICAL IMPORTANCE: E : IVRT can be used to predict LVFP in dogs with mild left-sided CHF induced by rapid pacing.