Cardiac Emergencies
WSAVA 2002 Congress
Virginia Luis Fuentes, MA VetMB PhD CertVR DVC MRCVS DipACVIM (Cardiology)
The Ohio State University, Dept of Veterinary Clinical Sciences
Columbus, OH, USA

Urgent cardiac disorders include severe congestive heart failure, rapid / severe tachyarrhythmias, severe bradyarrhythmias, cardiac tamponade, aortic thromboembolism and caval syndrome. It is important to recognize the condition, and stabilize the animal as quickly as possible before further investigations and carried out.

History and physical examination: assess quickly but efficiently. Always handle gently and quietly-any stress in handling can kill the patient, but you must be able to assess the patient effectively.

Sedation: If the animal is distressed and becoming frantic, sedation may decrease oxygen consumption thereby improving the patient's condition, as well as allowing you to conduct your assessment. On the other hand, if the animal is using all its ventilatory reserve at rest, sedation may depress respiration enough to cause further decompensation. For dogs, combinations of acepromazine (0.03 mg/kg) and an opiate (buprenorphine 0.015 mg/kg or butorphanol 0.2-0.4 mg/kg) can be given intramuscularly. For cats, doses of acepromazine (0.1 mg/kg) and butorphanol (0.2 mg/kg) may be used.

Radiography: Positioning animals for radiography often causes distress, which may prove fatal in dyspneic animals. It is often better to make an initial assessment based on physical exam, and delay radiography until the animal is more stable. If radiography is essential, avoid placing the animal on its back.

Is Pleural Effusion Present? Perform thoracocentesis if necessary. Rather than obtaining radiographs, it is often safer to attempt thoracocentesis if you suspect there is a large pleural effusion. This can be a life-saving measure if an effusion is present, and generally does little harm if there is no effusion (but use a small butterfly cannula)

Arterial Blood Pressure? Many animals with poor cardiac output will be hypotensive, which will require specific therapeutic measures. A noninvasive technique for measuring arterial pressure is invaluable (e.g., a Doppler ultrasonic or oscillometric technique).

ECG? ECG monitoring equipment should be readily available, and you should be able to interpret the common serious arrhythmias!

Oxygen: Have available, administer safely and effectively. Provide oxygen by plastic bag, face mask, cage, or tent if the patient will tolerate it. If not, the airflow of a fan to the face. Just allowing the animal to rest quietly in a cage will decrease oxygen requirements. Respiratory arrest due to hypoxia may be very amenable to resuscitation if you can ventilate the animal effectively. Have a range of endotracheal tubes handy, with a means of ventilation (ambubag, or oxygen with a suitable circuit)

Tabulate and trend important vital signs. Temperature, respiratory rate and depth, breath sounds, heart rate, heart rhythm, membrane color and refill time, pulse strength, attitude, and noninvasive arterial blood pressure should all be monitored and recorded, so that trends can be identified. A steadily increasing respiratory rate or falling arterial blood pressure should signal the need for more aggressive therapy.

CONGESTIVE HEART FAILURE

In congestive heart failure, the key features are excess fluid retention associated with raised atrial pressures. Elevated left heart filling pressures lead to pulmonary edema, whereas biventricular failure often leads to pleural effusion. Both may be life-threatening events. Ascites is not usually life threatening, and does not require emergency treatment in itself.

Cardiogenic Pulmonary Edema

Pleural Effusion

Respiratory distress

Increased respiratory effort

No stridor/ stertor

Distended chest

Pale or cyanotic mucous membranes

Pale or cyanotic mucous membranes

Weak pulses

Quiet lung sounds ventrally

± Murmurs / gallops /arrhythmias

Loud breath sounds dorsally

± Inspiratory crackles (alveolar edema)

Ventral dullness on percussion

Nasal frothing / coughing up pink frothy fluid

"Scalloping" or "leafing" of lung lobes on radiographs

"White-out" on radiographs

Cardiogenic Shock

Signs of low cardiac output/ cardiogenic shock include: low arterial pressure, pale mucous membranes, prolonged capillary refill time, hypothermia, and cold extremities.

Causes of CHF in dogs

 Mitral Valve Regurgitation

 Dilated Cardiomyopathy

 Cardiac Tamponade

 Congenital heart disease

 Endocarditis

Causes of CHF in cats

 Restrictive Cardiomyopathy

 Dilated Cardiomyopathy

 Hyperthyroidism

 Congenital disease

 Anemia

Hospital Treatment of CHF

Initial management of cardiogenic pulmonary edema is the same, regardless of cause.

 Furosemide 2-6 mg/kg IV, repeat initial dose hourly until response

 Oxygen by bag, cage or intranasal

 Nitroglycerin ½-4cm percutaneously q 8 hours

 Carry out further work-up once stable; may need to continue for 24-48 hours while starting oral therapy

After initial therapy, further investigations are indicated to determine the cause of CHF.

Mitral regurgitation

In dogs with mitral regurgitation, the mitral regurgitant volume can be significantly reduced (by 50% in some cases) by using an arterial dilator such as hydralazine. This cannot be used if the arterial pressure is already low.

Add oral hydralazine

 Start therapy with furosemide, oxygen and nitroglycerin. If no response within an hour, repeat furosemide

 Add hydralazine at 0.5-3.0 mg/kg PO q12hours

Dilated cardiomyopathy / cardiogenic shock

Add intravenous dobutamine

 Start therapy with furosemide, oxygen & nitroglycerin. Allow the patient 15-30 minutes at rest to stabilize and prepare dobutamine solution.

 Start dobutamine at 2.5 µg/kg/min, and increase up to 10 µg/kg/min

 Watch for adverse effects (tachycardia, arrhythmias, seizures)

 After 48 hours of therapy, reduce the dobutamine rate by 50% each 2 hours then stop

Congestive heart failure with pleural effusion

 Furosemide, oxygen and nitroglycerin should be administered

 Thoracocentesis should be performed using a butterfly cannula or angiocath. One side of the chest is often sufficient.

Arrhythmias

Treat if:

 Hemodynamically significant

 Life-threatening (unstable rhythm that may degenerate into lethal rhythm)

Ventricular Tachycardia

Rapid, repetitive ventricular extrasystoles can decrease arterial blood pressure and lead to signs of hypotension; in addition, some ventricular tachycardias are electrically unstable and may deteriorate to ventricular fibrillation.

In the absence of CHF, treat sustained ventricular tachycardia if:

 Very rapid (>200/min)

 Causing hypotension (<90 mmHg systolic)

 Animal is symptomatic

 Suspect risk of ventricular fibrillation

 Confirm the rhythm diagnosis of VT with an ECG

 Check serum potassium levels

 For sustained VT, administer lidocaine (2 mg/kg/minute bolus; repeat up to 8 mg/kg total dose over 10 minutes)

 If successful, start constant rate infusion at 50 to 70 µg/kg/min

 Avoid propranolol and cimetidine

 Do not use lidocaine in cats except at very low dosages

 Alternative to lidocaine in dogs-procainamide 2 mg/kg/minute

URGENT BRADYARRHYTHMIAS

Sinus bradycardia with ST segment changes

May be associated with hypoxia, may be warning sign of impending cardiopulmonary arrest

Check airway/ventilation, anesthesia/sedation, body temperature, electrolytes

 Consider atropine / epinephrine

Atrial standstill (hyperkalemia)

Counteract adverse effects of hyperkalemia

 IV fluids (0.9% NaCl)

 Calcium gluconate (0.5ml/kg of 10% solution slowly over 5-10 mins)

3rd degree atrioventricular block

Dogs should be referred for pacemaker implantation; the ventricular escape mechanism is fragile, and animals may die suddenly. Cats are often more stable, and may present with intermittent 3rd degree AV block.

CARDIAC TAMPONADE

Tamponade occurs when sufficient pericardial fluid accumulates within the pericardial space to increase the intrapericardial pressure above right atrial pressure, causing compression of the right heart. Affected animals may present with weakness (acute pericardial effusions-low output) or right-sided heart failure (chronic accumulation of pericardial effusion). Physical findings include muffled heart sounds, distended jugular veins, arterial hypotension, ± pulsus paradoxicus.

Diuretic therapy is not effective-the effusion must be drained.

Pericardiocentesis

A catheter or trocar system is used via a right-sided approach (ideally guided by echocardiography initially) or by the palpable cardiac impulse. The ECG is monitored for arrhythmias. Lidocaine is infiltrated locally around the entry site. The patient is placed in a slightly oblique lateral position. The needle/catheter is advanced through the skin and deliberately into the pleural and pericardial space using on hand as a "stop" to prevent sudden penetration. The pericardium can often be detected as it is punctured. If the heart is struck, the needle will "grate" and premature ventricular beats will occur. Once fluid is moving into the catheter hub, the needle is advanced 1-3 mm further and then held stable while the catheter is advanced into the space and manually secured. Owing to the relatively inelastic properties of the pericardium, the removal of even small amounts of effusion may be very beneficial and cause a rapid fall in the intrapericardial pressure.

AORTIC THROMBOEMBOLISM

Embolization of left atrial thrombi into the systemic circulation may occlude blood flow to peripheral arteries in cats with severe myocardial disease. Affected cats have an acute onset of signs, with severe pain and distress. Generally one or both hindlimbs is cold and pulseless, and congestive heart failure may develop at the same time.

 Analgesia (torbutrol 0.2 mg/kg SQ q8h combined with acepromazine; alternative = 10 cm2 fentanyl patch; 25 ug/hr release).

 Fluid therapy to maintain urinary output (unless there is concurrent pulmonary edema).

 Sodium bicarbonate (1 mEq/kg, IV over 2-5 minutes) for metabolic acidosis and hyperkalemia from muscle necrosis and reperfusion. This can be repeated.

 Antibiotic therapy effective vs. anaerobic infection (e.g., ampicillin, amoxicillin).

 Heparin (200 to 300 i.u. kg, IV, then subcutaneously every 8 hours for 48-72 hours)

 Acepromazine subcutaneously every 8 hours

Speaker Information
(click the speaker's name to view other papers and abstracts submitted by this speaker)

Virginia Luis Fuentes, MA VetMB PhD CertVR DVC MRCVS DipACVIM (Cardiology
The Ohio State University, Dept of Veterinary Clinical Sciences
Columbus, OH, USA


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