Cardiology emergencies (Proceedings)

Technicians familiar with cardiac emergencies can respond quickly and appropriately to minimize suffering and maximize the chance of success of treatment for the patient.

One of the most common veterinary cardiac emergencies is respiratory distress due to congestive heart failure. These patients can vary in stability from mild changes to collapse and cardiac arrest. The trick to dealing with these patients is to be able to perform diagnostics without stressing the patient unduly, and to know when to abandon diagnostics in favor of treatment. For instance, cats in respiratory distress can be both dangerous to technicians and clinically fragile. They can be difficult to handle for performing diagnostics, and attempting to take radiographs can push them too far. If CHF manifests as pleural effusion, the fluid can be tapped, stabilizing the patient and making them much safer to handle for diagnostics, both to themselves and the technician.

Ideally, radiographs are performed, and if CHF due to pulmonary edema is present, the first line of treatment is furosemide administration. Furosemide delivered intravenously will act more quickly than if it is administered IM or SQ, but it may not be possible to place an IV catheter or give an IV injection if the patient is not stable. Patients in respiratory distress may also benefit from sedation, as they may be excessively agitated or anxious. Sedation should be undertaken with caution, however. Nitroglycerin ointment may also be applied to the inside of an ear to facilitate vasodilation. "Nitro" should be applied with a glove, and the ear should be marked so that those who handle the patient do not touch the area with a bare hand, as it also causes vasodilation when applied to the skin of humans. If the owner visits their pet, they should also be made aware of the Nitro. Other medications may be used to treat acute CHF, but they require more intensive monitoring as well as IV access. Dobutamine, for instance, increases cardiac output, but it may also increase the heart rate, especially in patients with atrial fibrillation. Nitroprusside is a potent afterload reducer, which reduces the load on the heart, but also drastically reduces blood pressure, which must be monitored carefully.

More advanced therapy includes the use of mechanical ventilation in an ICU setting with critical monitoring. This obviously requires a very dedicated owner; veterinarian, often a critical specialist; and experienced technicians. Patients in respiratory distress may experience respiratory fatigue, and mechanical ventilation under anesthesia can help these patients rest until they can breathe again. The choice to ventilate is not made lightly, as it requires a significant financial commitment from the owner and advanced monitoring from the ICU staff.

Another cardiac emergency that may cause respiratory distress is pericardial effusion (PE), or collection of fluid within the pericardial space. Other clinical signs of PE include acute collapse, hypotension, vomiting, and signs of right sided heart disease. When the pericardial sac fills with fluid, pressure on the right side of the heart causes cardiac tamponade. This occurs when the right heart collapses and restricts filling. Physical exam findings often reveal muffled heart sounds, hypokinetic pulses, and pulsus parodoxus. Pulsus parodoxus is a variation in pulse intensity with respiration. Again, the goal of treating PE should address the patient's condition while determining the cause. An echocardiogram should ideally be performed if the patient is stable enough. The reason for this is to determine the cause of the effusion. One of the most common causes of PE is hemangiosarcoma (HSA), an aggressive vascular tumor that may only be detectable when effusion is present. The most common site of HSA is on the right atrium or right ventricle. The median survival time of dogs with PE due to HSA is 11 days with a single pericardiocentesis. In contrast, other causes of PE including heart base tumors, malignant mesothelioma, and idiopathic pericarditis carry a much better prognosis, especially when surgical removal of the pericardium is performed.

A rare cause of pericardial effusion is left atrial perforation. This occurs when mitral regurgitation constantly hitting the left atrial wall causes a jet lesion and eventually erodes through the wall. These patients present with a history of a murmur and sudden severe collapse, often accompanied by signs of pain. Signs of extreme weakness may be mistaken for neurological disease. These patients do not typically respond to pericardiocentesis, as removal of the effusion may disturb a clot holding blood in the left atrium. It can be difficult to treat these cases. Furosemide will cause further hypotension, and fluids will cause overload on the diseased valves. If a patient with left atrial perforation arrests and chest compressions are performed, this will only hasten the condition, forcing blood out of the heart and possibly rupturing the pericardial sac. The best course of action is to treat these patients gently, and be aware that the prognosis is grave.

Severe arrhythmias, either bradycardia or tachycardia, may also present as an emergency. Bradycardia may be due to sick sinus syndrome, high grade second degree or third degree atrioventricular block. Clinical signs may be lethargy or collapse. These patients typically do not respond to anticholinergics, and placement of a pacemaker is indicated. A temporary pacemaker may be useful to stabilize these patients until a permanent one can be placed.

Patients with ventricular or supraventricular may also present on emergency. These arrhythmias may be paroxysmal or sustained, and they also cause collapse and lethargy. The heart rate associated with ventricular tachycardia is generally over 200 beats per minute, and may even get as high as 300 or 350 beats per minute. Because ventricular fibrillation results from ventricular tachycardia, treatment is crucial. Intravenous boluses of lidocaine repeated every five minutes up to three times will typically "break" v-tach. Lidocaine may cause vomiting or seizures if given too quickly or if a larger volume is given. The treatment for seizures associated with lidocaine toxicity is diazepam. After the initial boluses are effective, a lidocaine CRI is often used to control the arrhythmia in the ICU setting.

Sustained supraventricular tachycardia (SVT) will also cause collapse and lethargy. These arrhythmias do not typically deteriorate into ventricular fibrillation, but they will have hemodynamic consequences. Sometimes, the heart rate associated with SVT will be as high as 400 beats per minute. SVT may manifest as atrial fibrillation or flutter, or re-entry tachycardia. Injectable antiarrhythmics, including calcium channel blockers like diltiazem or verapamil, can be used to break the rhythm. Vagal maneuvers, including ocular pressure, carotid sinus massage, or airway occlusion may also break the rhythm. One interesting way to break the rhythm is with a precordial thump. This involves striking the patient over the heart on the left thorax while it is laying in right lateral recumbency. This delivers a small depolarization of two to five Joules to the heart and resets the rhythm.

Aortic thromboembolism is another cardiac emergency. ATE, or saddle thrombus, can result from severe cardiac disease in cats, but it is rare in dogs. Other causes of ATE include pulmonary neoplasia and hyperthyroidism. These cats present often very painful, and both or either hindlimb, as well as a forelimb, may be affected. Stabilizing these patients should include pain medication as soon as possible. In a retrospective study of cats with ATE, a rectal temperature at or greater than 98.9 F was associated with a 50% chance of survival to discharge.