Cardiac emergencies I Flashcards
The three main determinants of the heart’s work:
cardiac preload
cardiac afterload
myocardial contractility
Cardiac preload is
the amount of ventricular stretch at the end of diastole, the filling of the ventricles.
can be called “venous return” as well but is not so accurate cause preload isn’t venous return alone, it also includes ventricular wall compliance.
Cardiac afterload is
The pressure that the heart must work against to eject blood during systole.
Preload is affected by: (3)
venous return
compliance of ventricular wall
circulating blood volume
Factors affecting cardiac afterload: (5)
Systemic hypertension
(Aortic valve will not open until the pressure generated in the left ventricle is higher than the elevated pressure in the aorta.)
Aortic stenosis
Aortic regurgitation
Mitral regurgitation
Alpha-2-agonists (vessel constriction)
Contractility equals the
Ability of the heart muscle to eject a stroke
volume at a given prevailing afterload.
Contractility is Affected by: (5)
morphology of the myocardium
sympathetic activation
drugs
parasympathetic activation
hypercapnia
Heart disease versus heart failure
Heart disease = any structural abnormality in the heart that does not necessarily cause heart failure.
Heart failure=- a pathophysiological condition in which the heart is unable to function at a level that ensures adequate perfusion of organs and tissues.
Heart failure pathophysiology can be divided into two broad groups:
volume overload issues
and
diastolic disorders
volume overload issues in heart failure can be caused by: (3)
Systolic dysfunction (DCM makes systolic contraction insufficient)
Valvular insufficiency (leaky valve means some blood squirts back in making it too much total volume)
Left to right shunt (PDA = persistent ductus arteriosus)
diastolic disorders in heart failure can be caused by: (3)
- Thick and rigid ventricular walls (diastolic relaxation is insufficient, blood backs up and causes left atrial dilation/hypertrophy and effusions further up the chain)
- Abnormal ventricular relaxation
- Pericardial problem
Name the 4 main Cardiac Emergencies in Small Animals
Congestive heart failure
Cardiac tamponade
Arrhythmogenic disease
Thromboembolic disease
Many of these diseases are life threatening and must be diagnosed quickly and efficiently to provide relief of symptoms and to avoid delays in definitive treatment.
Left atria size compared to left ventricle?
Atria should be max 1/3 the size of the ventricle.
Low output or forward heart failure refers to when
The heart cannot provide blood flow adequate for metabolic demands.
Weakness and collapse
Congestive heart failure or– backward failure refers to when
Increased venous pressure causes fluid accumulation in lungs or body cavities.
Breathlessness
Congestive heart failure is characterized by 3 main features.
Poor myocardial contractility
Chronic cardiac overload
Cardiac injury
Congestive heart failure Three phases:
- initiating cardiac injury or insult (often undetected)
- phase of compensation, but with clinically silent progression
- the onset of clinical CHF signs
Congestive heart failure Categories: (4)
Primary myocardial failure
Volume overload
Systolic pressure overload
Reduced ventricular compliance
But the distinctions between them blur
with disease progression and patients with advanced heart failure develop features of several categories.
Common causes of congestive heart failure in dogs:
Degenerative mitral valve disease (MVD) (cavalier, yorkie etc.)
Dilated cardiomyopathy (DCM) (great dane, dobermen, boxer etc.)
Other causes can be:
infectious endocarditis
cardiac neoplasia
heartworm disease
Common cause of congestive heart failure in cats:
Hypertrophic cardiomyopathy (HCM)
Other causes can be:
infectious endocarditis
cardiac neoplasia
heartworm disease
History/anamnesis in congestive heart failure cases may include: (7)
may or may not have a history of a previous cardiac problem
may or may not be on medications
may have a dry and harsh cough, especially at night, in the early morning or after exercise
may be restless at night
exercise intolerance
syncope
weight loss
Heart disease predisposition in what breeds?
Small breed dogs:
- Cavalier King Charles Spaniels
- Dachshunds
- Miniature and Toy Poodles
Cats:
- Maine coon
Large breed dogs:
Doberman Pinscher and
Boxer have a higher predisposition for
cardiomyopathy, which leads to heart failure.
connection between dental health and heart disease
animals with very poor teeth have a constant state of inflammation in the gingiva. bacteria constantly enter the blood stream from the bad mouth = constant bacteremia.
bacteria can lodge in different organs, including the heart, leading to endocarditis which is heart valve inflammation, which in turn can lead to degeneration over time and an audible murmur.
Why might a heart disease dog cough more in the mornings?
During the day time the heart may be compensating with a higher heart rate but over night the HR decreases so once the animal begins to wake up and move around in the morning, the compensation has not been “on” meaning it may exhibit signs such as cough.
Common Clinical signs of heart failure. (7)
cough (dog)
dyspnea
lethargy
syncope or episodic weakness
abdominal distention (dog)
partial to complete anorexia
most cats in HF do not present for cough or
abdominal distention
what is sinus rhythm on an ECG?
its sinus when each P wave has a QRST complex
Dogs with HF secondary to MVD typically have what types of audible changes?
loud systolic murmurs and tachycardia (>120 bmp).
The absence of a murmur or a soft murmur (grade II or less) or the presence of a respiratory sinus arrhythmia in a
small-breed dog with respiratory signs usually refutes the diagnosis of HF.
Dogs with DCM typically have what types of audible changes?
soft or barely audible systolic murmurs and tachyarrhythmias.
atrial fibrillation in a dog or cat with suspect HF, is very suggestive of HF
The physical examination of a cat with HF can unfortunately be
somewhat nonspecific.
The heart rate can be fast, normal, or slow.
Up to 30% of cats may not have an obvious arrhythmia, murmur, or gallop.
Cats in HF are not uncommonly hypothermic.
empiric therapy in heart disease cases.
In some patients with significant respiratory distress, empiric therapy to stabilize patients is started even before any further diagnostic tests are performed if the signalment, history, and physical examination are suggestive of HF.
Initial empiric therapy typically includes:
- administration of parenteral furosemide
- oxygen
- sedation
Diagnostics in cases presenting with overt heart disease.
The TFAST and AFAST ultrasound and focused echocardiogram are performed with patients in sternal recumbency while receiving oxygen supplementation typically after a low dose of sedation.
The examination is brief and minimally stressful to patients and is generally less stressful than performing a thoracic radiograph.
Goals:
- identifying pleural and pericardial effusions
- left atrial enlargement
Focused thoracic ultrasound is especially useful in
cats with suspect HF because both the physical examination and radiographic findings in cats with HF are notoriously nonspecific.
Cats with HF usually have With pleural effusion, and in that case the heart can be clearly visualized by ultrasound, allowing accurate assessments of chamber dimensions, specifically left atrial size.
a common manifestation of feline HF
Pleural effusion, a common manifestation of feline HF, obscures the cardiac silhouette, lungs, and vasculature radiographically.
With pleural effusion, the heart can be clearly visualized by ultrasound, allowing accurate assessments of chamber dimensions, specifically left atrial size.
A left atrium/aorta ratio of 2.0 or greater is very suggestive of
HF.
The left atrium is most commonly indexed to the aorta in a right-sided, short-axis view at the base of the heart or a long-axis view.
Normally, the left atrium/aorta ratio is less than 1.5 in cats and less than 1.3 in dogs.
Thoracic radiographs in Left-sided HF:
(3)
Dorsal displacement of trachea
Prominent pulmonary veins
Pulmonary edema
(interstitial pattern in image)
Thoracic radiographs Right-sided HF:
(3)
Pleural effusion
Enlarged caudal vena cava
Hepatomegaly
Use what for assessment of cardiomegaly.
Vertebral heart score (VHS)
Cardiac biomarkers (2)
Cardiac biomarkers are blood tests for heart disease.
pro B-type natriuretic peptide (NTproBNP)
cardiac troponin I (cTnI)
NTproBNP is
a peptide hormone released by the ventricles in response to increased stretch elevated in dogs and cats with active congestive HF.
used as an early cardiac biomarker (snaptest).
proBNP SNAP test (cats)
Can be used when
Can be used when testing “suspicious”
patients (for example, pedigree cat,
breathing problem).
Negative SNAP – heart disease is unlikely
Positive SNAP without clinical signs– HCM
is possible – send to a cardiologist
Positive SNAP with signs of dyspnea –
handled as a patient with heart failure.
NB May give false positive results!
Treatment of cardiac emergency.
The immediate goal of emergency therapy is to reduce abnormal fluid accumulations and to provide adequate or improved cardiac output.
Supplemental oxygen (cage/incubator or nasal catheter)
Sedation if needed
If the patient is dyspneic and anxious
Butorphanol is very effective 0.1 – 0.2 mg/kg.
Place an intravenous catheter, treat with furosemide and/or vasodilators if appropriate.
Additional treatments:
possible thoracocentesis
abdominocentesis
bronchodilators
antiarrhythmic agents
Treatment with Furosemide
is a loop diuretic, is a mainstay in the management of congestive HF, regardless of the cause.
Despite its usefulness in HF
management, furosemide never technically improves cardiac output - it reduces volume overload.
Describe Treatment using Pimobendan.
0.25 – 0.3 mg/kg q 12 h
dual mechanism of action (inodilator = dilates coronary vessels) calcium-sensitizing drug that improves contractility (positive inotrope) with minimal effects on myocardial oxygen consumption.
phosphodiesterase inhibition, primarily leading to a balanced vasodilation (arterial and venous) the role of pimobendan in feline HF is still evolving, typically added when a cat with HF has left ventricular systolic dysfunction, significant pleural effusion, renal insufficiency, or severe refractory pulmonary edema.
will NOT work in cats with hypertrophic heart disease.
Vasodilators that may be used in cardiac emergent cases: (3)
Amlodipine 0.05 – 0.1 mg/kg PO
Nitroglycerine 2% ointment – transdermally
Enalapril 0.5 mg/kg PO q12 h
Additional treatments:
possible thoracocentesis
abdominocentesis
bronchodilators
antiarrhythmic agents
Cardiac tamponade/ Pericardial effusion is
Physiologic state in which the pericardial effusion causes an increase in intrapericardial pressure resulting in impaired ventricular filling and low
cardiac output.
The most common cause of pericardial effusion in older dogs is
neoplasia, most commonly right atrial
hemangiosarcoma in large-breed dogs and
chemodectomas (heart base tumors) in
brachycephalic dogs.
The most common cause of pericardial effusion in cats is
CHF.
Clinical signs of Cardiac tamponade/pericardial effusion. (7)
collapse
lethargy
exercise intolerance
cough/retching
shortness of breath
abdominal distention
inappetence
Physical examination in pericardial effusion. (4)
muffled heart sounds
Tachycardia
weak pulse
pulsus paradoxus
Pulsus paradoxus =
paradoxical pulse, is an abnormally large decrease in stroke volume, systolic blood pressure (a drop more than 10 mmHg) and pulse wave amplitude during inspiration.
Normally, blood pressure drops less precipitously than 10 mmHg during inhalation.
Pulsus paradoxus is a sign that is indicative of several conditions, most commonly pericardial effusion.
Diagnostics for suspected pericardial effusion.
Echocardiography is the most sensitive and specific modality. You cannot confirm pericardial effusion with xray, xray can only give you a suspicion of it.
- amount and echogenicity of the pericardial fluid
- thickness of the pericardium
- presence of a cardiac tumor
Diastolic right atrial and sometimes ventricular collapse.
ECG abnormalities in pericardial effusion. (2)
sinus tachycardia
low amplitude QRS
Treatment of pericardial effusion and tamponade.
Pericardiocentesis is the only effective treatment of immediate relief of cardiac tamponade.
Do NOT give furosemide in pericardial effusion. Why? Because diuretics and vasodilators may be harmful because they will reduce ventricular filling and cause further hypotension with hypovolemia.
In which cardiac emergency should you most definitely NOT give furosemide?
in pericardial effusion!
Why?
Because diuretics and vasodilators may be harmful because they will reduce ventricular filling and cause further hypotension with hypovolemia. -> death.
Describe Pericardiocentesis procedure
Mild sedation is sometimes needed.
Some patients are so hemodynamically compromised that sedation is not necessary. Patients are placed in sternal or lateral recumbency.
ECG should be performed during the procedure to monitor for ventricular arrhythmias.
The pericardiocentesis site is prepared aseptically. Lidocaine is infused at the puncture site on the RIGHT hemithorax between the third and sixth intercostal
spaces just above the costochondral junction.
Ultrasound or thoracic radiography is helpful to find the best site for the pericardiocentesis.
A 3-mL syringe is attached to the end of the
catheter and constant negative suction is applied.
Once in the pericardial space, the catheter is advanced over the needle stylet and extension tubing, a 3-way stopcock and 60-mL syringe are attached, and drainage of the fluid begins.
Why is pericardiocentesis prognosis poor in dogs compared to cats?
Because in dogs, pericardial effusion is usually due to heart neoplasm but in cats its usual due to CHF which is more treatable than heart cancer.
Why is pericardiocentesis performed on the RIGHT hemithorax and not on the left?
On the right side of the chest, the heart’s anatomical layout positions major coronary vessels (like the left coronary artery) and structures such as the left atrium away from the insertion site.
By accessing the pericardium from the right side, veterinarians reduce the risk of accidentally puncturing these critical structures, which could cause severe complications.
The left side of the chest houses the larger lung lobe and major structures like the aorta and the esophagus.
Entering from the left could risk lung puncture or damage to these adjacent structures. The right side provides a clearer path to the pericardial sac with fewer obstructions.
Most pericardial effusions are haemorrhagic and can be similar in appearance to blood.
If there is concern for possible intracardiac
puncture, a sample of the fluid should be
obtained and visualized for clot formation.
Why?
Pericardial effusion should not clot.
If there are clots - then you’re in the heart.
