SAEVA Congress 2018 Proceedings | 12-15 February 2018 | ATKV Goudini Spa
incremental test. In such instances parameters like V 200 are low and others like HR 10
are high and the speed at which HR max is reached is slower than expected for a
healthy horse. Interpretation of the findings is not always straightforward because the
results can be influenced by the ambient temperature, the patient’s fitness level,
level of hydration and the presence of co-existing disease, particularly those that are
associated with pain or interfere with O 2 uptake and/or transport. Abnormal HR
responses to exercise are normally also characterized by a prolonged HR recovery
period. In fit, healthy horses, HR can be expected to drop dramatically in the first 2
mins post-exercise, generally being <112 after this time. Horses with clinical
problems frequently have comparatively prolonged periods post-exercise with HRs in
the range of 112-130bpm. While it is important to have a good sense of the normal
HR response to exercise, the detection of an abnormal response is not necessarily
indicative of cardiovascular disease. Rather, such aberrant findings indicate that
further clinical investigation is warranted.
Some abnormal HR responses to exercise can be associated with arrhythmias,
however, not all arrhythmias are pathologic or easily detectable. With the exception
of atrial fibrillation, detection and interpretation of arrhythmias occurring during or
immediately after exercise can be difficult. An ECG recorded at a HR >200 can be
difficult to decipher even with the assistance of computer software programs.
Arrhythmias are more common in the first 2 mins post-exercise than during exercise
and are usually not sustained. Whether during or after exercise, premature
supraventricular complexes are the most commonly detected arrhythmias, occurring
in up to 50% of racehorses, 13 and they are usually regarded as innocuous unless
they occur in spates of more than 1 beat or recur with regularity. Ventricular
premature complexes are less frequent and more problematic, especially if
superimposed on the T wave as this is when the myocardium is most vulnerable to
the development of ventricular fibrillation and sudden death. Interpreting the clinical
significance of arrhythmias associated with exercise is a real challenge especially
with respect to when they might be primary or secondary to other pathological or
temporary abnormalities like electrolyte changes and severe academia. The reader
is referred to the ACVIM consensus statement on exercise arrhythmias for a more
comprehensive discussion of this vexing topic (see Reef VB, et. al, J Vet Int Med,
2014; 28:749). In summary, arrhythmias must be interpreted in terms of other clinical
findings if they exist. For instance, if the patient has auscultatory and/or
echocardiographic findings compatible with impaired cardiac function and has a
history of reduced performance, the arrhythmia might be significant. If, however, it is
an incidental finding on a horse being evaluated for performance potential, it is
should best be noted as an isolated but clinically insignificant finding.
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