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.fox@amcny.org; Tel: 1 212 329 8606

OVERVIEW

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

therapy.

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.

Cardiogenic Shock

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

and arrhythmias.

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.