circulatory 1 Flashcards
cardio patient - what do we want to figure out about the heart problem with our clinical exam?
Is it a primary cardio-vascular disease?
Or inappropriate cardiovascular response?
cardiovascular aspects of the physical exam
◦ Heart
◦ Hydration (skin turgor: know normal)
◦ Edema
◦ Peripheral veins
◦ Peripheral pulses
◦ Mucous membranes
lactating dairy cow HR, and non-lactating
Heart rate range of 60-80 is for lactating dairy cow
◦ Relaxed, well socialized, non-lactating cow may well be lower
◦ Variation is normal > Interaction between sympathetic and parasympathetic tone
tachycardia - centrally mediated contributions
◦ Cortical stimulation
◦ Catecholamine release
tachycardia from increased peripheral demand - common reasons
◦ Lactation: increased metabolic rate
◦ Increased physical activity: exercise, eating
4 common reasons for tachycardia, very broadly
- “Decrease” in blood volume (hypovolemia)
- Severe anemia: (anemic anoxia) carrying capacity (eg. neonatal isoerythrolysis)
- Reduced cardiac function
- Arrhythmia
Tachycardia due to “Decrease” in blood volume (hypovolemia)
- types? when might we see this?
Absolute: blood loss, dehydration, loss of capillary integrity (burn)
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Relative: change in capacitance of the system
◦ Change in venous capacitance
◦ Change in peripheral vascular beds (resistance vessels) change blood pressure
◦ Peripheral vasodilation → loss of peripheral resistance
> Toxemia/ endotoxemia/ septicemia
> Pyrexia → high metabolic rate, release vasoactive substances
Tachycardia due to reduced cardiac function
- what is the problem here?
- types of issues that cause this
Intrinsic: heart cannot respond to demands
◦ Pericardial disease: cannot fill
◦ Myocardial disease: abnormal muscle function
◦ Endocardial - especially valvular: cannot maintain fill
◦ Other diastolic (filling) problems
tachycardia due to arrhythmia - what might we hear?
◦ May or may not sound irregular
Bradycardia
- common reasons
- Hypoglycemia
- Decreased catecholamine levels/lack of response
- Conservation of energy
- Vagal stimulation
- Hyperkalemia
- Hypokalemia
- Increased intracranial pressure
common cause of vagal stimulation leading to bradycardia
◦ Vagal indigestion cases
how does hyperkalemia lead to bradycardia?
what about hypokalemia?
Hyperkalemia (dysrhythmias also common)
◦ Loss of concentration gradient across cell membrane (decrease membrane potential (less
negative)
◦ Decrease available Na channels - slow conduction
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Hypokalemia
◦ Usually increases risk of phase 4 depolarization and tachycardia
◦ But profound hypokalemia has been associated with AV block and severe bradycardia
Increased intracranial pressure - how can this lead to bradycardia?
◦ Cushing reflex
◦ Arterial pressure less than ICP → sympathetic stimulation heart → vasoconstriction, inotropy,
increased CO→ increased BP → baroreceptor response→ vagal stimulation → bradycardia
Key point:
◦ If heart rate or rhythm does not fit clinical picture, what should we do?
Then run an ECG
- LL gound, Ra-, La+
shock, types (6)
A critical state of hypoperfusion of tissues
◦ Tissue perfusion decreased to point insufficient to meet needs
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Cardiogenic shock
◦ Pump failure: arrhythmia, heart disease
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Hypovolemic shock
◦ Blood volume below critical level
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Toxic shock
◦ Toxin causing failure of microvasculature, effects on heart, progressive
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Endotoxic shock
◦ Bacterial toxin with effects on microvasculature
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Septic shock
◦ Septicemia with effects on organs and vasculature
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Neurogenic shock
◦ Severe bradycardia secondary to intense emotional stimuli, vagal stimulation or CNS trauma
most common type of heart failure we see in cattle
congestive, right sided
Right-sided heart failure clinical signs
◦ Increased HR (tachycardia)
◦ Decreased: appetite, exercise tolerance and decreased production
◦ Venous engorgement (jugular vein distension)
◦ Ventral edema (limbs rarely or end stage)
◦ Ascites not easily detected (not large amount)
◦ Cool extremities
◦ If exercise intolerance is extreme: tachypnea, +/- dyspnea
◦ Animal stands with elbows abducted
◦ Arrhythmias may occur end stage, but are not common
Left-sided heart failure
- prevalence
- clinical signs
- progression
◦ Rare in cows as lone left sided heart failure
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◦ Tachycardia
◦ Exercise intolerance
◦ Weak pulse
◦ Weight loss > More obvious left-sided. Right-sided may be masked due to volume overload.
◦ Increased pulmonary pressures
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◦ If slow, then right heart has time to compensate
◦ May see very little to no respiratory signs
◦ First signs of heart failure may be right heart failure
◦ If occur fast, acute pulmonary edema can develop > Dyspnea, frothing at mouth/nares
Heart Failure
Clinical course
◦ Once clinical signs of heart failure start to develop most cases survive < a month
◦ With minimal stress may survive longer
◦ Complicated cases may last days > Acute left-sided, Congenital heart disease with secondary endocarditis
Heart Failure
Treatment
prognosis
◦ Once clinical signs have developed
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◦ Minimize stress
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Supportive care:
◦ Diuretics, digoxin in valuable animals
◦ Underlying disease likely to cause permanent damage > even if could treat (eg. nutritional deficiency, endocarditis)
◦ Calving may improve signs if they worsened end lactation
◦ May only be buying time to salvage/slaughter
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◦ Prognosis grave
Disorders of Heart Rhythm
- what they indicate
- types we see, prevalence?
Most persistent arrhythmias in cattle indicate heart disease
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Supraventricular dysrhythmias are rare
◦ Atrial fibrillation is the most common
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Cattle do show sinus arrhythmia
◦ Some variation in rhythm is expected
◦ Correlation with respiratory cycle
Atrial fibrillation
- what is it?
- cause?
- frequency, significance
- Lack of coordinated atrial electrical activity
- Caused by abnormal pulse conduction → resulting in unidirectional conduction block and random re-entrant activation of the atria
- Some of these signals to hit AV node and conduct to ventricle → resulting in irregular ventricular rhythm
- Infrequent > But always of clinically significance
Atrial fibrillation
Risk factors, general
◦ Electrolytes and acid-base imbalance
◦ GI disease or peritoneal irritation
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◦ Atrial enlargement (organic heart disease) > Not recommended to treat
◦ Atrioventricular valve regurgitation
◦ Ventricular failure
◦ Myocarditis
◦ Autonomic nervous system imbalance
◦ Anesthetic drugs and tranquilizers
◦ Unknown
Atrial fibrillation
Risk factors for cattle in particular
◦ Gastrointestinal disease
◦ Foot rot and pneumonia
◦ Hypokalemia, hypocalcemia, and hypochloremia
◦ Metabolic alkalosis
◦ Experimentally: Metabolic alkalosis + hypokalemia
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◦ Dx. more frequent in dairy than beef
