Cardiorespiratory problems

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Cardiorespiratory signs are a common reason for presentation in canine practice, and in acute situations involving collapse or dyspnoea can be a source of stress to clinician and owner alike. This chapter will present a clinical approach to the following signs: cough; dyspnoea, heart murmur; and arrhythmia. : Pericardiocentesis; Thoracocentesis and thoracic drain placement.

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24.1 Starting on the left side of the dog, the stethoscope is placed on the chest wall just caudal to the elbow where the heart is loudest; this will approximate to the mitral valve (M) where the first heart sound (S1 or ‘lub’) will be most audible. In order to hear the aortic valve (A), the stethoscope is slid craniodorsally into the axilla, such that S1 fades and the lower pitched second heart sound (S2 or ‘dub’) becomes more notable. The pulmonary valve (P) is found by dropping slightly cranioventrally from the aortic valve to a position very close to the sternum behind the foreleg; the sounds of this valve are quieter than the other two due to the lower pressures on the right side of the heart. The tricuspid valve is found on the right side of the body (T) and represents the place where S1 is loudest on this side.
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24.2 Lateral radiographs are centred approximately at the caudal border of the scapula and two-thirds of the way down the thorax, with the forelegs drawn forward and a wedge placed under the sternum to ensure that the sternum and spine are level. Occasionally in some breeds, especially Bull Terriers, this wedge may need to be under the spine to achieve the same result. DV radiographs are preferred for assessment of the cardiac silhouette; although if it is safe to put the animal on its back (i.e. there is no dyspnoea or pleural effusion) a VD view may offer greater information on the lung fields. The radiograph is centred in the midline at the caudal border of the scapulae, with the forelegs once again drawn forward. Effort is required to ensure that none of the body is rotated, in order to keep the thorax straight.
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24.3 Some patterns commonly seen on thoracic radiography. Bronchial patterning is characterized by an increase in radiopacity of the lower bronchial walls, seen as ‘tramlines’ and ‘doughnuts’ in the lung fields. They may be associated with bronchitis, angiostrongylosis, asthma/allergy and chronic respiratory obstruction (e.g. laryngeal paralysis or brachycephalic obstructive airway syndrome). This image shows the dorsocaudal lung fields of a dog with angiostrongylosis; the pattern is bronchointerstitial and numerous bronchial rings are visible (good examples arrowed). Diffuse interstitial patterning is more subtle and is seen simply as a general obscuring of detail. It may be associated with pulmonary oedema, angiostrongylosis, bronchopneumonia and diffuse lymphoma in lung tissue. This image is from a dog with cardiac failure; bronchial patterning is also visible. Nodular interstitial patterns show multiple radiopaque nodules. They may be seen with metastatic neoplasia, , fungal disease or pulmonary abscessation. This image is from a Boxer with pulmonary metastasis of a distant adenocarcinoma. An alveolar pattern represents disease in the terminal bronchioles and alveoli, such as severe oedema, haemorrhage, angiostrongylosis or bronchopneumonia. Lung tissue is consolidated, showing a general increase in radiopacity so that darker bronchi are highlighted as they course through the lung lobe, so-called ‘air bronchograms’. Occasionally, an entire lung lobe will be consolidated, seen as a region of marked increased radiopacity with sharp borders. Vascular patterns are seen as increased opacity and size of the pulmonary blood vessels. They are best assessed by measuring the cranial lobar vessels as they cross the 4th rib on a lateral radiograph, where they should not be wider than the rib itself, or the caudal lobar vessels as they cross the 9th rib on a DV view, where again they should be smaller in width than the rib; on the lateral view, the artery is dorsal to the vein (separated from it by the radiolucent bronchus); on the DV view the artery is lateral to the vein (separated from it by the radiolucent bronchus). Pulmonary venous enlargement is indicative of left-sided cardiac congestion, whilst arterial engorgement is associated with obstructive disease such as angiostrongylosis or thromboembolism; an equal increase may be seen in cases of pulmonary hypertension, either idiopathic or secondary to diseases such as hyperadrenocorticism or renal insufficiency.
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24.5 Stenotic nares is a common problem in brachycephalic breeds, as in this 1-year-old Shih Tzu cross. The photograph shows the dog after surgical correction of the right nostril. (Courtesy of Tim Hutchinson)
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24.6 Radiograph from a Springer Spaniel with an idiopathic megaoesophagus. The radiopaque walls of the oesophagus are seen as they course through the mediastinum (arrowed), whilst the air in the oesophagus does not change the appearance of the lung fields within these boundaries. In this Golden Retriever megaoesophagus is secondary to thymic neoplasia, visible as a radiopaque mass cranial to the heart (bracketed red).
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24.7 Severe respiratory distress due to neurogenic pulmonary oedema after a choking incident in a 6-month-old Golden Retriever. Notice the pale mucous membranes, extended neck, abducted elbows and reluctance to have an oxygen mask placed over the face. (Reproduced from the ; courtesy of Dr Ken Drobatz, University of Pennsylvania)
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24.9 Lateral radiograph of a 9-year-old neutered Border Collie bitch with multicentric lymphoma. Pleural effusion is seen as radiopaque areas in the ventral aspect of the radiograph, causing scalloping of the lung lobes. There is dorsal displacement of the trachea in this case, though this may be due to a cranial mediastinal mass rather than to the effusion.
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24.10 Pneumothorax produces collapse of one or both lung lobes such that their edges are no longer seen to reach the chest wall. The lungs themselves are more radiopaque than normal owing to their collapsed state. Radiolucent air is seen surrounding the lungs, giving a much darker appearance than normal, and the heart is usually raised from the sternum, with the cardiosternal ligament highlighted. This radiograph is from a German Short-haired Pointer with a ruptured pulmonary bulla; the stone in the stomach is incidental.
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24.11 An idiopathic pericardial effusion in a small, cross-breed terrier prior to drainage. Echocardiogram, again prior to drainage. Percutaneous drainage via the right 5th intercostal space, using a direct pericardiocentesis set. The effusion was drained twice percutaneously. On a third episode the dog was treated surgically with a subtotal pericardectomy via a right-sided thoracotomy, to good effect. Once the fluid can drain into the much larger pleural cavity, the patient can usually cope and the fluid can be resorbed by the pleura.
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24.13 Echocardiogram of a pericardial effusion caused by a clearly apparent haemangiosarcoma of the cardiac wall in a Greyhound. Such tumours may be secondary to splenic haemangiosarcoma, but this one was not. The patient was euthanased. LA = left atrium; LV = left ventricle; PE = pericardial effusion; RA = right atrium; RV = right ventricle.
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24.14 Even a quick ultrasound scan of the heart will allow assessment of left atrial size, which is not likely to be normal if cardiac failure is the cause of dyspnoea. In dogs, left atrial size (LA) is compared with the width of the aorta (Ao). Both measurements are taken at the level of the aortic valve in the right parasternal short-axis view, to allow standardization of the measurement irrespective of the size of the dog, as the aortic diameter will increase in direct proportion to bodyweight and not change with disease state. An LA:Ao ratio of =1.6 is considered to be normal. These images are taken from two dogs, both presenting with dyspnoea due to pulmonary congestion but with markedly different aetiologies. Normal echocardiographic measurement of the left atrium, with an LA:Ao ratio of 1.5. This measurement quickly suggested that cardiac disease was not the cause of the problem; bronchopneumonia was subsequently diagnosed. In this image of the Staffordshire Bull Terrier in Figure 24.16 , the left atrium is clearly enlarged (LA:Ao ratio = 2.4). This allowed a cardiac diagnostic pathway and treatment plan to be promptly pursued.
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24.16 Lateral radiograph of an 8-year-old Staffordshire Bull Terrier with congestive cardiac failure due to DCM. There is left atrial tenting (red arrows), dorsal displacement of the trachea (blue arrow) and a straight caudal border to the heart (yellow line). There is also increased sternal contact (green line) suggesting that the right side of the heart is also enlarged.
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24.17 The components of a normal P–QRS–T complex in lead II. Atrial fibrillation in an Irish Wolfhound. There is an irregularly irregular rhythm of normally shaped, narrow and upright QRS complexes (often of differing magnitudes) without normal P waves; the P waves may be replaced by f waves associated with fibrillation of the atria, but these can be difficult to see in the baseline in many cases. A single VPC is also present. In this ECG from the same Irish Wolfhound, VPCs are seen as wide and bizarre complexes (without P waves), which occur earlier than would be expected with the predominant rhythm (arrowed). They may be seen in runs of three or more, sometimes merging into one another so that the normal baseline is lost, and these will be defined as ventricular tachycardia. ECG from a Boxer with kennel cough. SVPCs are recognized as a narrow, upright complex with a P wave that comes sooner than expected (arrowed). Runs of SVPCs will create supraventricular tachycardia, which is more significant. In this trace, the SVPCs interrupt an otherwise normal sinus rhythm; they resolved when the infection resolved and were not significant.
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24.18 A Boxer with intermittent collapse wearing a Holter monitor. Arrhythmogenic right ventricular cardiomyopathy (a form of ‘Boxer cardiomyopathy’) was diagnosed.
Image of The author finds the use of a surgical pen to mark the rib numbers and incision site useful, to ensure that confusion over which intercostal space is which does not occur once drapes have been applied.
The author finds the use of a surgical pen to mark the rib numbers and incision site useful, to ensure that confusion over which intercostal space is which does not occur once drapes have been applied. The author finds the use of a surgical pen to mark the rib numbers and incision site useful, to ensure that confusion over which intercostal space is which does not occur once drapes have been applied.
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Image of Courtesy of Nick Bexfield
Courtesy of Nick Bexfield Courtesy of Nick Bexfield
Image of Courtesy of Nick Bexfield
Courtesy of Nick Bexfield Courtesy of Nick Bexfield
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