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==Introduction==

==Introduction==

Cats that present with aortic thromboembolism almost invariably have significant underlying cardiac disease and often show overt signs of congestive heart failure. Treatment of the condition can be very challenging both in the prevention of reperfusion injury and management of existing heart problems.  

Cats that present with '''aortic thromboembolism''' almost invariably have significant '''underlying cardiac disease''' and often show overt signs of '''congestive heart failure'''. Treatment of the condition can be very challenging both in the prevention of reperfusion injury and management of existing heart problems.  

==Pathogenesis==

==Pathogenesis==

Thromboemboli commonly lodge in the distal aorta and iliac arteries. They are formed within the heart - dislodging and entering the aorta. There are three factors that cause ischaemic damage in the limbs:

'''[[Thromboembolism|Thromboemboli]]''' commonly lodge in the '''[[Vascular System - Anatomy & Physiology|distal aorta and iliac arteries]]'''. They are formed within the heart - dislodging and entering the aorta. There are three factors that cause [[Ischaemia|ischaemic damage]] in the limbs:

1) The thromboembolus itself

'''1)''' The '''thromboembolus''' itself

2) A series of subsequent vasoconstrictive events that decrease collateral circulation.  

'''2)''' A series of subsequent '''vasoconstrictive events''' that decrease collateral circulation.  

3) Reperfusion injury following the breakdown of the clot and return of collateral circulation.   

'''3)''' '''Reperfusion injury''' following the breakdown of the clot and return of collateral circulation.   

The consequence of this is ischaemic neuromyopathy. The muscle is quite sensitive to ischaemic damage - with the clot causing a rigor mortis effect in the tissue. The peripheral nerves are fairly resistant to structural damage but they undergo rapid functional change. This functional failure can be reversed it blood flow is restored before structural nerve damage occurs (several hours later). The amount of structural nerve damage determines the level of permanent nerve damage.   

The consequence of this is '''ischaemic neuromyopathy'''. The '''muscle''' is quite '''sensitive''' to ischaemic damage - with the clot causing a '''rigor mortis''' effect in the tissue. The '''[[Peripheral Nervous System - Response to Injury|peripheral nerves]]''' are fairly '''resistant''' to structural damage but they undergo rapid functional change. This functional failure can be reversed it blood flow is restored before structural nerve damage occurs (several hours later). The amount of structural nerve damage determines the level of permanent nerve damage.   

==Signalment==

==Signalment==

As mentioned, cats normally have underlying cardiac disease - most commonly [[Hypertrophic Cardiomyopathy|hypertrophic cardiomyopathy (HCM)]].

As mentioned, cats normally have underlying '''cardiac disease''' - most commonly [[Hypertrophic Cardiomyopathy|hypertrophic cardiomyopathy (HCM)]].

==Clinical Signs==

==Clinical Signs==

The most common presenting signs are acute rear limb paralysis, depression, pain and dyspnoea. The paralysis may be unilateral or bilateral. On clinical exam there is an absence of femoral pulses in the affected limbs and the cranial tibial and gastrocnemius muscles feel firm on palpation. The footpads are cold and discoloured and there is no response to noxious stimuli or movement in the lower limb. Additional findings include a lack of tone in the anal sphincter, bladder distention and abdominal pain. Pain and underlying cardiac disease can cause tachycadia and tachypnoea. Additional signs of cardiac disease may be detected on cardiac auscultation such as a murmur, arrhythmia or gallop rhythm.

The most common presenting signs are '''acute rear limb paralysis, depression, pain and dyspnoea'''. The paralysis may be unilateral or bilateral. On clinical exam there is an '''absence of femoral pulses''' in the affected limbs and the [[Canine Hindlimb - Anatomy & Physiology|cranial tibial and gastrocnemius muscles]] feel firm on palpation. The '''footpads are cold''' and '''discoloured''' and there is '''no response to noxious stimuli''' or '''movement''' in the lower limb. Additional findings include a lack of tone in the anal sphincter, bladder distention and abdominal pain. Pain and underlying cardiac disease can cause '''tachycardia and tachypnoea'''. Additional signs of cardiac disease may be detected on cardiac auscultation such as a '''murmur, arrhythmia''' or gallop rhythm.

 

Reperfusion injury, which occurs several hours after clot formation may cause '''depression, [[Arrhythmias Overview|arrhythmias]] and cardiac conduction abnormalities'''. This can be fatal. Swelling and [[Oedema|oedema]] of the limbs is seen once reperfusion occurs.  

==Diagnosis==  

==Diagnosis==  

====Blood Pressure Reading====

====Blood Pressure Reading====

Blood pressure readings should be taken on all four limbs as this allows comparison between the normal and affected legs and indicated

Blood pressure readings should be taken on all four limbs. This allows comparison between the normal and affected legs and provides information on the cardiovascular status of the animal.

====Echocardiography====  

====Echocardiography====  

====Radiography====

====Radiography====

Thoracic

Thoracic radiography is useful to identify any [[Pulmonary Oedema|pulmonary oedema]] or pleural effusions caused by the underlying cardiac disease.

====Biochemistry====

====Biochemistry====

====Electrocardiography====  

====Electrocardiography====  

==Treatment==

[[Heart Failure - Pathophysiology|Congestive heart failure]] should be treated with the '''[[Heart Failure, Treatment|diuretic frusemide]]''' - which should clear '''[[Pulmonary Oedema|pulmonary oedema]]''' and relieve respiratory signs. '''[[Fluid therapy|Fluid therapy]]''' is required for the treatment of '''[[Shock|cardiovascular shock]]''' and hyperkalaemia - however it is important to closely monitor and adjust the fluid rate to prevent the worsening of pulmonary oedema. '''[[Analgesia]]''' should be provided although [[Phenothiazines|acepromazine]] has been used historically, '''[[Analgesic Drugs|butorphanol]]''' is recommended in recent texts. The '''anticoagulant heparin''' should also be administered to prevent the clot expanding.  

''Treatment includes supportive therapy with fluids and diuretics, use of a vasodilator such as acepromazine, and an anticoagulant such as heparin, aspirin, or warfarin.

 

Heparin is generally used in the acute phase, and warfarin for long-term anticoagulant therapy.

'''Surgery''' to remove the clot can be performed, however it must be done within hours of the thromboembolus forming and requires specialist facilities not usually available in general practice. Therefore it is not normally performed. Clot dissolution can be attempted using streptokinase and urokinase but again this is normally restricted to referral centres.

Clot dissolution has been achieved using streptokinase and urokinase.

 

'''Hyperkalaemia''' and the associated cardiac rhythm and conduction disturbances that occur secondary to reperfusion injury should be treated with '''fluid therapy and appropriate drugs''' (calcium borogluconate, insulin, glucose, sodium bicarbonate or sodium chloride).  

Amputation of the left atrial appendage has also been suggested to eliminate the nidus for thrombus formation.

 

In most cases, surgery is not rewarding and medical management is preferred.''

Anticoagulant therapy with '''warfarin, aspirin and clopidogrel''' may be given to the cat long term to prevent recurrence and cardiac medications such as '''frusemide, ACE inhibitors''' should be considered for the management of cardiac disease. Analgesia is not required at this point but''' physical therapy''' should be performed for a minimum of 4-6 weeks whilst the limb recovers. It is important to check the limb for any '''wounds or secondary infection''' and treat these appropriately.

==Prognosis==

==Prognosis==

'''Prognosis is entirely dependent on the level of ischaemic injury'''. Several features can give an indication of prognosis but ultimately only time will tell is the cat has the ability to regain function in the affected limb. Obviously less severe clinical signs on presentation suggests a ‘better’ prognosis. The type of cardiac disease present also affects prognosis, with a better prognosis in cases of [[HCM]] with minimal atrial enlargement and no congestive heart failure. It is reported that approximately one third of cats survive the initial thromboembolus and reperfusion injury. '''The condition is thought to recur in up to a quarter of cases'''.

''Prognostic indicators

As with most diseases, the severity of the disease

and the resulting clinical presentation are variable. Clinical signs that indicate a ‘better’ prognosis include pale pink pad colour, tail movement,

good anal tone, upper thigh muscle control, normal mental acuity, eupnoea and normal body temperature. Cats have a better prognosis if they have

cardiomyopathy. Left atrial size also has prognostic significance, with severe dilation being a more

ominous sign. The prognosis is worse if congestive  

heart failure is present''

 

''A recent study showed that affected cats had a 34% chance of surviving the initial thromboembolic episode; those that did had an average survival of 11.5 months.

Prognosis varies with the severity of the embolic event, degree of ischemia, evidence of abdominal organ infarction and severity of the underlying cardiac disease.''

==Prevention==

==Prevention==

The presence of spontaneous contrast within an enlarged atria during echocardiography is seen in at-risk cats. These animals can be treated with prophylactic anticoagulants such as aspirin and.....

Cats with cardiac disease may have routine echocardiograms to monitor the progresion of disease. The presence of '''spontaneous contrast''' within an enlarged atria is seen in at-risk cats. These animals can be treated prophylactically with anticoagulants such as '''aspirin'''.

{{Learning

{{Learning

Moise, NS (2007) '''Presentation and management of thromboembolism in cats''' ''In Practice 2007 29: 2-8''

Moise, NS (2007) '''Presentation and management of thromboembolism in cats''' ''In Practice 2007 29: 2-8''