Sunday, July 24, 2011
Notes from July 2011 St. Louis AVMA Conference-Critical Cardiology Care
These are papers from the July 2011 St. Louis AVMA conference. I’ve edited them to delete some of the vet only jargon and for space considerations. If you see (…) that means that information has been deleted due to these considerations. The ones listed here include HCM, and other heart related papers, treatments, papers on x-rays and echos, thrombosis, kidney disease, idiopathic cystitis, pain management, anesthesia and cardiac disease, supplements and other hazards for pets, and some other basic information I hope is helpful.
CRITICAL CARE CARDIOLOGY
Philip R Fox, DVM, Dipl ACVIM, ECVIM-CA (Cardiology), ACVECC
The Animal Medical Center
Philip.email@example.com; Tel: 1 212 329 8606
Immediate interventions are generally required for at least five life threatening conditions-cardiogenic
pulmonary edema, cardiogenic shock, ventricular underfilling (pericardial
tamponade), hemodynamically unstable arrhythmias, and arterial thromboembolism.
EVALUATING THE CRITICAL PATIENT
Assessment of the unstable patient is aided by a careful history, complete general
examination, and complete data base.
Noninvasive Monitoring of Hypoxemia (Pulse Oximetry) …Pulse oxymetry is a
noninvasive technique to allow continuous monitoring of arterial oxyhemoglobin saturation…Pulse oximetry measures functional hemoglobin saturation…and thereby assesses arterial oxygenation. It
does not assess ventilation (CO2 elimination). Hypoxemia may be a late onset sign of
deteriation in some cases of respiratory failure, especially when compensatory tachypnea has
maintained normal oxygen levels…Arterial blood gas analysis should be
considered whenever pulse oximetry estimation is in question.
Noninvasive Blood Pressure Monitoring Hypertension may predispose certain "target" organs
to injury, particularly the eyes, kidneys, and cardiovascular and neurovascular systems.
Hypotension is a common consequence of shock, dehydration, and certain drug toxicities.
Systolic blood pressure >160 suggests hypertension; SBP>200 mmHg recorded on 2
occasions at least 24 hours apart indicate hypertension, unless the animal was excited…
SBP <90 indicates hypotension.
Central Venous Pressure (CVP) CVP directly measures pressure in the great thoracic veins
as blood returns to the right heart. Serial or continuous CVP measurement helps assess right
heart filling and status of intravascular volume. Evaluation of the direction of change in CVP
measurements over time is more relevant than basing diagnostic/therapeutic changes on
isolated measurements…Elevated CVP measurements suggest either right ventricular failure or
intravascular volume overload.
Electrocardiography Assessment of heart rate and rhythm provide information about cardiac
chamber enlargement, implies the presence of severe pericardial or pleural effusion, and can
help assess certain suspected systemic and metabolic disorders (e.g., marked disturbances of
potassium or calcium, ischemia, infarction). Continuous ECG monitoring, event recorders, or
Holter recordings are useful to detect transient arrhythmias.
Radiography The radiograph 1)confirms disease suspected from the history and physical
examination, 2) assesses disease severity, 3) distinguishes between cardiac and respiratory
disease, 4) confirms tube/catheter placement, 5) screens for unsuspected conditions, 6)
discovers complications, and 7) and helps monitor (from repeated studies) response to
Echocardiography and Abdominal Ultrasound Examinatons-diagnostic ultrasound assists
cardiac examination when the heart is obscured by pleural effusion; diagnoses pericardial
effusion; provides quantitative assessment of cardiac structure (valves; chamber dimensions,
wall thickness); assesses systolic (contractile) and diastolic function; quantifies gradients via
Doppler echocardiography; detects disturbances of blood flow; detects intracavitary masses
(clots, tumors); and helps characterize congenital and acquired heart diseases.
Acute Congestive Heart Failure (Pulmonary edema)
In dogs CHF results most commonly from volume overload caused by chronic degenerative
valvular disease (severe mitral regurgitation) or dilated cardiomyopathy. In cats diastolic heart
failure associated with hypertrophic or restrictive cardiomyopathy is the predominant
underlying condition. Less common etiologies include aortic insufficiency, left-to-right shunting
(PDA, arteriovenous fistula), and high output states (thyrotoxicosis). Treatment requires
aggressive measures to resolve the congestive state and improve cardiopulmonary function.
Furosemide (lasik) is given as IV boluses (2-4mg/kg q 30-60min) or by constant rate infusion.
Vasoactive drugs are added to promote venodilation and/or arterial dilation. Typically, this may
include nitroglycerin ointment for mild to moderate edema. In states of life threatening edema
in the dog, the potent vasodilator sodium nitroprusside is administered by CRI (2-20ug/kg/min
with constant arterial blood pressure monitoring). Alternatively, hydralazine, a potent arteriolar
dilator, can be given (2mg/kg PO bid) when pulmonary edema results from mitral
regurgitation. Inotropic support using dobutamine (5-15ug/kg/min constant rate infusion) is
indicated when severe myocardial failure or cardiogenic shock is present (e.g., dilated
cardiomyopathy). The potential role of pimobendan in this circumstance has not been clarified
but may provide benefit as well. Digoxin is often considered (dog- 0.005-0.01mg/kg lean body
weight q 12 hrs; cat- ¼ of 0.125mg tablet q 24-48 hrs), especially when right-sided heart
failure or atrial fibrillation is present. Antiarrhythmic therapy is administered when needed to
suppress or abolish ventricular tachyarrhythmias, or to control ventricular rates with
supraventricular tachyarrhythmias such as atrial fibrillation. Supplemental O2 administration is
provided. Mechanical removal of effusion is performed if necessary. ACE inhibitors and
pimobendan are included in chronic management strategies.
Ideally, reversible causes of heart failure should be treated if present. Myocardial failure has
been associated with taurine and carnitine deficiency in the dog, and with taurine deficiency in
the cat…Other systemic and metabolic disorders may cause or
contribute to heart failure including endocarditis, myocarditis, pheochromocytoma, diabetes,
and hyperthyroidism. Heartworm disease is a treatable cause of right-sided CHF.
With recurrent heart failure, upward drug titration may be necessary. Serum digoxin
concentrations should be monitored. Diuretic resistance may occur as heart failure
progresses. Some animals are likely to benefit from intravenous furosemide therapy which
has higher bioavailability, or a second and third diuretic (e.g., thiazide, 5 to 20 mg daily, or
spironolactone- 12.5 to 25 mg once to twice daily). It is prudent to assess BUN, creatinine,
electrolytes and blood pressure during chronic therapy.
Myocardial failure is most commonly associated with dilated cardiomyopathy. Less frequent
etiologies include chronic volume overload (eg, mitral regurgitation, left-to right shunts) or
sepsis. The principal hemodynamic feature of cardiogenic shock is systemic hypotension
associated with reduced ventricular pumping (ie, myocardial failure/systolic dysfunction).
Pulmlonary edema, systemic congestion, hypotension, and tissue hypoxia result. Acute
management may require inotropes (dobutamine CRI), diuretics to reduce congestion,
vasodilators such as sodium nitroprusside. ACEI, digoxin, pimobendan, and control of sepsis
Cardiac Tamponade (Ventricular Underfilling)
Conditions which interfere with return of blood to the heart may result in decreased cardiac
preload, compensatory neuroendocrine activation, and a clinical condition known as cardiac
tamponade . This is generally associated with pericardial disease (typically neoplasia in dogs;
or FIP or idiopathic effusions in cats). Less common causes include space occupying atrial or
ventricular masses including blood clots or tumors. Initial management requires therapeutic
pericardiocentes. Avoid using drugs that decrease preload or cause vasodilation.
Hemodynamicaly unstable arrhythmias
Tachyarrhythmias may depress cardiac output, cause hemodynamic impairment or
hypotension, and result in organ ischemia. Shortened diastolic filling decreases coronary
blood flow, reduces myocardial oxygen supply, causes ischemia and results in more serious
arrhythmias. Certain tachyarrhythmias may deteriorate by becoming electrically unstable.
Hemodynamic impact of tachyarrhythmias are influenced by factors related to underlying
cardiac disease…Because cardiac output = heart rate x stroke volume, sustained tachycardia may reduce
cardiac output and artial blood pressure. In atrial fibrillation with rapid ventricular response,
ventricular filling shortens due to loss of atrial contraction, variation in cycle length and high
ventricular rate. This is worsened by concurrent myocardial dysfunction (eg, dilated
cardiomyopathy)…Rapid, sustained ventricular tachycardia decreases cardiac output, results in hypotension and organ ischemia. Ventricular flutter causes precipitous deterioration and all circulation ceases with ventricular fibrillation…multifocal atrial or ventricular tachycardia are more likely to compromise
hemodynamics, especially if ventricular function is abnormal…The underlying state of ventricular function, systemic and metabolic alterations, and concurrent drug or anesthetic agents influence electrical stability. Electrical
instability is increased by rapid ventricular rates and multifocal impulse origination…
The underlying ventricular function, systemic and metabolic alterations, and concurrent drug or anesthetic agents influence electrical stability…Supraventricular arrhythmias may be treated with digitalis
glycosides, calcium channel blockers, beta blockers, and other agents. Acute management of
ventricular tachycardia includes treatment of the underlying cause and lidocaine. Pacemaker
implantation may be required to treat high grade AV block.
References available upon request.