FRANK J. MILNE STATE-OF-THE-ART LECTURE


Fig. 34. Huge pericardial effusion in a horse with pericardi- tis. Notice the right ventricular diastolic collapse (arrow) that is indicative of cardiac tamponade and the small cardiac chamber sizes imaged in the right parasternal four-chamber view. RA, right atrium; RV, right ventricle; LA, left atrium; LV, left ventri- cle; PE, pericardial effusion. The top right of the image indicates the orientation of the transducer which is dorsal in this image.


Fig. 35. Initial drainage of the pericardial sac following place- ment of an indwelling 28 French chest tube into the pericardial sac at the left 5th intercostal space in a horse with pericarditis and cardiac tamponade.


Pericardial Drainage and Lavage


Pericardial drainage and lavage is recommended for all horses with an effusion large enough to success- fully insert a large bore chest tube into the pericar- dial space.183 The amount and type of pericardial fluid present will determine if an indwelling cathe- ter can be placed or whether only a fluid sample can be obtained. Cytology, culture, and sensitivity test- ing of the fluid should be performed in both situa- tions. The optimal site for the placement of a catheter for pericardiocentesis should be determined echocardiographically but is usually the left 5th in- tercostal space, above the lateral thoracic vein and below the coronary groove. If possible, a large-bore Argyle chest tube (24–32 French) is placed in the pericardial sac under ultrasonographic guidance (Fig. 35). Repeated drainage, lavage of the pericar- dial sac with sterile isotonic fluids, and instillation of intrapericardial antimicrobials are possible with this catheter.183 Intrapericardial corticosteroids have been used successfully in horses when pericar- dial inflammation persists and culture results are negative.178


Significance/Prognosis


The prognosis for horses with pericarditis has im- proved markedly over the past 40 years. Treat- ment failure was common, with the risk of constrictive pericarditis developing later, resulting in a guarded to poor prognosis for affected horses.151,165,166,174,184,185 The use of large-bore in- dwelling tubes for repeated pericardial drainage and lavage markedly improved their prognosis.150,156,163 The incidence of constrictive pericarditis also de-


112 2018  Vol. 64  AAEP PROCEEDINGS


creased. Early diagnosis and aggressive systemic antimicrobial and anti-inflammatory therapy is also important, both in these horses and in those with pericardial effusions too small for indwelling peri- cardial tube placement.153 With the abovemen- tioned changes, survival rates for horses with pericarditis has markedly improved. These horses are also able to return successfully to perfor- mance.150,155,156,163 Even in affected young Thor- oughbred racehorses, expected sales prices and successful racing careers were possible following re- covery from pericarditis.186


7. Evaluation of Arrhythmias with Emphasis on Diagnosis, Management, and Impact on Performance, Life Expectancy, and Horse and Rider Safety


Second Degree Atrioventricular Block


The 2°AVB is a normal arrhythmia in fit horses, occurring in 15–18% of horses during a routine ECG2,3 but detected in 44% of horses during contin- uous ECG monitoring.1 2°AVB is usually a physi- ologic arrhythmia associated with high resting vagal tone and disappears with excitement or exercise.39 Sinus arrhythmia usually accompanies 2°AVB and disappears with the disappearance of 2°AVB.187 The administration of sympathomimetic or parasym- patholytic drugs should also make 2°AVB disappear. Physiological 2°AVB is an occasional disruption in an otherwise normal rhythm. In normal fit horses, 2°AVB is occasionally detected in the immediate postexercise period.39 Horses with 2°AVB usually have a slow or low normal resting heart rate (24–30 bpm). The underlying rhythm is regular, with an


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