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Cardiology Vet Information
- Atrial Fibrillation
- Cardiology Drug Formulary
- Accelerated Idioventricular Rhythm (AIVR)
- Aortic Thromboembolism
- Blood Pressure Measurement
- Choosing an ECG recorder
- Collapse in Dogs
- Collapse in Boxer dogs
- DCM Supplementary Treatment
- ECG interpretation and report service
- Exercise Induced Collapse
- Feline Hypertrophic Cardiomyopathy (HCM)
- GDV and ventricular arrhythmias
- Treatment of Heart Failure in Dogs
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To assist vets whose patients have heart and lung problems, we have put together a range of informative pages which cover a number of the cardiology topics – we hope that you find them helpful.
Please feel free to view this information by following the links provided. If you have any queries, please do not hesitate to contact us.
Also see our Cardiac Interventions pages
Atrial fibrillation is one of the most common arrhythmias in dogs and is usually associated with a faster than normal heart rate. It frequently occurs in dogs with cardiac disease and it contributes to worsening of the clinical signs of congestive heart failure.
This section includes the drugs we use in cardiology and respiratory medicine and at the dosages that we would use, which sometimes variesa little from standard ‘textbook’ dosages. For detailed information regarding uses, contra-indications and side-effects the reader should consult appropriate formularies and the product data sheets.
Accelerated idioventricular rhythm (AIVR) is a descriptive term for a ventricular ectopic rhythm with a rate in between the rates of a ventricular escape rhythm (often 30-50/min in dogs and 90-110/min in cats), and a ventricular tachycardia (often >180/min)..
Amiodarone is an anti-arrhythmic drug used in humans for ventricular and atrial arrhythmias. It prolongs the repolarisation phase 3 of the action potential by blocking the K-channels. It predominantly has class 3 effects, but also some properties of all classes. However side effects are reported to be common in humans, including the effects on the eye, skin, thyroid, nervous system, liver, heart, lungs and urogenital system.
Over 90% of cases are associated with underlying heart disease. Diagnostic tips: The affected limb is usually painful, cold, cyanotic or pale, no or limited arterial pulse. Compared to blood taken from a normal limb, blood from an affected limb will have a lower blood glucose and higher serum lactate.
Hypertension and hypotension are found in many clinical scenarios. Hypertension can cause dramatic consequences (end target organ damage). Low blood pressure is less well appreciated compared to hypertension, but just as important.
An ECG machine required for diagnostic purposes is preferably a recorder rather than a monitor. In other words using an ECG monitor (used in perianaesthestic or intensive care monitoring) is not the ideal for diagnostic ECG recordings. It is best to have ‘separates’ – a recorder for diagnostic electrocardiography and a monitor for anaesthesia.
Indicated in dogs with refractory congestive heart failure signs (e.g. ascites), due to dilated cardiomyopathy or valvular endocardiosis, for more effective diuresis in addition (‘sequential nephron blockade’) to a loop diuretic (e.g. frusemide).
Brief and/or infrequent episodes of collapse present a diagnostic challenge, particularly when they are often normal at the time of examination. It is of paramount importance in such cases to obtain a detailed and thorough history – a 5 to 10 minutes consultation may not be sufficient. Either reallocating more time, or referral of the case, is therefore necessary.
Boxer dogs seem to present with collapse more than other breeds of dogs. Many appear to collapse occasionally in their life, although more commonly when younger – often referred to as ‘Boxer faint’. This might be a consequence of a vasovagal reflex following excitement or on rising from a sleep. However since dilated cardiomyopathy is not uncommon in Boxer’s and it often present initially with frequent arrhythmias and collapse, this is an important differential to screen for.
There is now significant evidence that beta blockers have a beneficial role in the treatment of mild to moderate heart failure with left ventricular systolic dysfunction. Recent evidence (in man) has shown that when beta blockers are added to a regime of diuretics and ACEIs they can substantially decrease mortality and morbidity; at 1.3 years, there was a 34% reduction in mortality, 44% reduction in sudden deaths and 20% reduction in hospital admissions.
To maximise the information that can be gained from ECG interpretation the following recording routine may be of help.
Exercise induced collapse (EIC) syndrome is a condition that has become recognised since the mid-1990s. There has been some published work in the USA in Labrador Retrievers (Shelton & Taylor 2002), but we also recognise a similar condition in Border Collies in the UK. EIC syndrome is primarily seen in athletically fit young Labradors or Collies less than 3 years of age.
Hypertrophic cardiomyopathy (HCM) is phenotypically described as hypertrophy of the left ventricle (without chamber dilation) in the absence of other cardiac or systemic diseases. It is considered a primary cardiomyopathy and part of the clinical diagnosis (ante-mortem) is therefore exclusion of other causes of left ventricular hypertrophy such as aortic stenosis, systemic hypertension, hyperthyroidism, infiltrative myocardial diseases, myocarditis and pseudo-hypertrophy such as occurs with an under-loaded or hypovolaemic left heart (eg. shock, blood loss, dehydration, severe pulmonic stenosis, rapid sustained tachyarrhythmias).
Approximately 40 to 50% of dogs with gastric dilation-volvulus (GDV) develop ventricular arrhythmias. These usually occur 12 to 72 hours after the onset of GDV. They occur secondary to myocardial ischaemia (decreased coronary perfusion), reperfusion injury, hypokalaemia, acidosis, hypoxia and myocardial depressant factors. The hypokalaemia can also make the arrhythmias resistant to anti-arrhythmic drugs which rely on a normal electrolyte balance.
Hydroxyurea (hydroxycarbamide) comes as 500mg capsules (Hydrea, Squibb). Dose for polycythaemia is approximately 50mg/kg twice a week to start – but try to work out a dose to avoid splitting the tablets.
Heart failure is the most common clinical presentation of dogs with heart disease.
Congestive heart failure (CHF) infers that there is a damming back of blood behind the failing heart, into the pulmonary (eg. pulmonary oedema) or systemic (eg. ascites) circulations. CHF is a sequel to many of the various causes of heart disease. Its treatment is very similar in most cases of adult heart disease (except pericardial effusion).