Hypertrophic cardiomyopathy is the most common form of heart disease that affects cats.1–5 The disease is characterized by diffuse or segmental hypertrophy of the left ventricular myocardium that involves the interventricular septum, left ventricular free wall, and papillary muscles.4 Dynamic left ventricular outflow tract obstruction attributable to SAM of the mitral valve occurs when enlarged papillary muscles pull the mitral valve into the outflow tract, which results in turbulence and, possibly, a decrease in CO.3,6 The incidence of SAM in cats with HCM is variable, but it is a labile condition that increases and decreases in severity as contractility changes.
The plasma concentration of cTnI is a sensitive and specific biochemical marker for myocardial damage. The plasma concentration of cTnI is increased in cats with HCM7–9; however, to our knowledge, plasma concentrations of cTnI have not been measured during the perianesthetic period.
Complications in anesthetized humans with HCM include congestive heart failure, supraventricular and ventricular tachyarrhythmias, and systemic hypotension.10–15 Hypotension develops in healthy cats and cats with HCM anesthetized with inhalation anesthetic agents because of the negative inotropic and systemic vasodilatory effects.16,17 Persistent hypotension in healthy anesthetized cats is treated by the administration of positive inotropes, such as dopamine and dobutamine. These drugs are expected to increase blood pressure by increasing CO.18 Blood pressure can also be increased by administration of α1-adrenergic receptor agonists, such as phenylephrine; however, this technique may be less desirable because CO and tissue perfusion may actually decrease.18
In contrast, for cats with HCM, it is hypothesized that administration of positive inotropes may induce or increase dynamic outflow tract obstruction, which would potentially reduce or limit CO. Additionally, by increasing myocardial work and o2, positive inotropes may compromise the balance between Mo2 and myocardial Do2 in patients with HCM. Alternatively, the administration of a vasoconstrictor may decrease the pressure gradient across the aortic valve, which would limit dynamic obstruction and potentially improve CO.6,12 Consistent with this, conscious cats with HCM and SAM that received medetomidine, a drug expected to increase SVR, had complete resolution of dynamic outflow tract obstruction as assessed by echocardiographic examination.19
These hypotheses have not been investigated in anesthetized cats with HCM. The purpose of the study reported here was to determine plasma concentrations of cTnI and cardiorespiratory effects attributable to incremental doses of dopamine and phenylephrine in hypotensive, isoflurane-anesthetized cats with severe, naturally occurring HCM. We hypothesized that dopamine would increase CO and the plasma concentration of cTnI more than would phenylephrine and that both dopamine and phenylephrine would effectively increase blood pressure.
Cardiac troponin I
Central venous pressure
End-tidal concentration of isoflurane
Left ventricular stroke work index
Myocardial oxygen consumption
Oxygen extraction ratio
Pulmonary artery occlusion pressure
Pulmonary artery pressure
Rate pressure product
Right ventricular stroke work index
Systolic anterior motion
Systemic vascular resistance
Systemic vascular resistance index
Ventricular premature contraction
Oxymorphone HCl, Endo Pharmaceuticals Inc, Chadds Ford, Pa.
22-gauge Insyte catheter, Becton-Dickinson, Sandy, Utah.
Midazolam HCl, Baxter Healthcare Corp, Deerfield, Ill.
Etomidate, Ben Venue Labs Inc, Bedford, Ohio.
Isoflurane, Piramal Healthcare Ltd, Andrah Pradesh, India.
Lactated Ringer's injection USP, Baxter Healthcare Corp, Deerfield, Ill.
Gaymar Industries Inc, Orchard Park, NY.
Bair Hugger 505, Augustine Medical Inc, Eden Prairie, Minn.
Introducer kit, Arrow International, Reading, Pa.
Thermodilution balloon catheter, Arrow International, Reading, Pa.
Central venous catheterization kit, Arrow International, Reading, Pa.
Beckman Medical gas analyzer LB1, Beckman Instruments, Schiller Park, Ill.
Dopamine HCl, Hospira Inc, Lake Forest, Ill.
Phenylephrine HCl, Baxter Healthcare Corp, Deerfield, Ill.
Medfusion 2010i, Medex Inc, Duluth, Ga.
Physiograph, Gould Instrument Systems, Valley View, Ohio.
Ponemah, version 3.0, Gould Instrument Systems, Valley View, Ohio.
COM-1, American Edwards Laboratories, Irvine, Calif.
ABL 800, Radiometer, Copenhagen, Denmark.
Meloxicam, Boehringer Ingelheim Vetmedica Inc, St Joseph, Mo.
Immulite 2000 analyzer, Siemens Healthcare Diagnostics Inc, Deerfield, Ill.
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