Page 183 - Small Animal Internal Medicine, 6th Edition

CHAPTER 7 Myocardial Diseases of the Dog 155

various other arrhythmias. Echocardiographic signs of poor Traumatic Myocarditis
regional or global ventricular systolic function, altered myo- Nonpenetrating or blunt trauma to the chest and heart is
VetBooks.ir cardial echogenicity, or pericardial effusion can be evident. In more common than penetrating wounds. Cardiac arrhyth-
mias frequently are observed after such trauma. Cardiac
dogs with persistent fever, serial bacterial (or fungal) blood
cultures could be useful. Serologic screening for specific
pression, or acceleration-deceleration forces. Other possible
infective causes might be helpful in some cases. Histopatho- damage can result from impact against the chest wall, com-
logic criteria for a diagnosis of myocarditis include inflam- mechanisms of myocardial injury and arrhythmogenesis
matory infiltrates with myocyte degeneration and necrosis. include autonomic imbalance, ischemia, reperfusion injury,
Endomyocardial biopsy specimens are currently the only and electrolyte and acid-base disturbances. Thoracic radio-
means of obtaining a definitive antemortem diagnosis, but graphs, serum biochemistries, cardiac troponin I concentra-
if the lesions are focal, the findings may not be diagnostic. tions, ECG, and echocardiography are recommended in the
assessment of these cases. Echocardiography can define pre-
Treatment existing heart disease, global myocardial function, and unex-
Unless a specific etiologic agent can be identified and treated, pected cardiovascular findings, but it may not identify small
therapy for suspected myocarditis is largely supportive. areas of myocardial injury.
Strict rest, antiarrhythmic drugs (see Chapter 4), therapy Arrhythmias usually appear within 24 to 48 hours after
to support myocardial function and manage CHF signs trauma. VPCs, ventricular tachycardia, and accelerated idio-
(see Chapter 3), and other supportive measures are used as ventricular rhythm (with rates of 60-100 beats/min) are
needed. Corticosteroids have not proven clinically beneficial more common than supraventricular tachyarrhythmias or
in dogs with myocarditis and, considering the possible infec- bradyarrhythmias in these patients. An accelerated idioven-
tive causes, are not recommended as nonspecific therapy. tricular rhythm often is manifested only when the sinus rate
Exceptions would be confirmed immune-mediated disease, slows; this rhythm is benign in most dogs with normal
drug-related or eosinophilic myocarditis, or myocarditis underlying heart function, does not require antiarrhythmic
unresponsive to other therapies. Nonsteroidal antiinflam- treatment, and disappears usually within a week of the
matory drugs could be considered in some cases. trauma. More serious arrhythmias (e.g., with a faster rate) or
hemodynamic deterioration may require antiarrhythmic
therapy (see Chapter 4).
SEPSIS-INDUCED MYOCARDIAL Avulsion of a papillary muscle, septal perforation, and
DYSFUNCTION rupture of the heart or pericardium have also been reported
Sepsis-induced myocardial dysfunction describes a syn- with cardiac trauma. Traumatic papillary muscle avulsion
drome of reversible myocardial depression that occurs in causes acute volume overload with acute onset of CHF. Signs
the setting of sepsis or other critical illness. This is a common of low-output failure and shock, as well as arrhythmias, can
and well-recognized phenomenon in human intensive care develop rapidly after cardiac trauma.
units and has also been described in dogs. The syndrome is
characterized by ventricular dilation and systolic dysfunc- Suggested Readings
tion (a DCM phenotype), and can involve both the LV and Primary Myocardial Disease
RV. Unlike idiopathic DCM, patients with sepsis-induced Baumwart RD, Orvalho J, Meurs KM. Evaluation of serum cardiac
myocardial dysfunction have normal or even high cardiac troponin I concentration in Boxers with arrhythmogenic right
output and low systemic vascular resistance. The underlying ventricular cardiomyopathy. Am J Vet Res. 2007;68:524–528.
mechanisms are multifactorial and unclear but likely include Beddies G, et al. Comparison of the pharmacokinetic proper-
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insensitivity, and mitochondrial or cytoskeletal abnormali- diomyopathy. J Vet Intern Med. 2006;20:104–110.
ties. Sepsis-induced myocardial dysfunction further com- Calvert CA, et al. Results of ambulatory electrocardiography in
promises perfusion in patients with septic shock and can overtly healthy Doberman Pinschers with echocardiographic
also lead to CHF. This syndrome is associated with wors- abnormalities. J Am Vet Med Assoc. 2000;217:1328–1332.
ened prognosis among humans with sepsis. Diagnosis is Calvert CA, et al. Association between result of ambulatory elec-
based on echocardiographic evidence of new LV dilation trocardiography and development of dilated cardiomyopathy
and systolic dysfunction in a critically ill patient. Cardiac during long-term follow-up of Doberman Pinschers. J Am Vet
biomarkers (particularly cardiac troponin I) can be used Med Assoc. 2000;216:34–39.
as screening tools to identify affected patients. Treatment Cunningham SM, et al. Echocardiographic ratio indices in overtly
healthy Boxer dogs screened for heart disease. J Vet Intern Med.
involves inotropic support with either dobutamine or pimo- 2008;22:924–930.
bendan, depending on the patient’s level of hemodynamic Dukes-McEwan J, et al. Proposed guidelines for the diagno-
compromise. If treatment for sepsis is successful and the sis of canine idiopathic dilated cardiomyopathy. J Vet Cardiol.
patient survives the period of critical illness, ventricular 2003;5:7–19.
size and function completely normalize (usually within Falk T, Jonsson L. Ischaemic heart disease in the dog: a review of
7-10 days). 65 cases. J Small Anim Pract. 2000;41:97–103.