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.
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
Hospital Treatment of CHF
Initial management of cardiogenic pulmonary edema is the same, regardless of cause.
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
Dilated cardiomyopathy / cardiogenic shock
Add intravenous dobutamine
Congestive heart failure with pleural effusion
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.
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
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
Atrial standstill (hyperkalemia)
Counteract adverse effects of hyperkalemia
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.
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.
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.
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
Virginia Luis Fuentes, MA VetMB PhD CertVR DVC MRCVS DipACVIM