Fig. 60. Simultaneous ECG rhythm strips obtained with continuous ECG monitoring demonstrating a period of torsade de pointes (large angled arrows). There is a series of ventricular complexes (small vertical arrows) that precede the period of torsades (only one VPC is visible in this figure), followed by a period of normal sinus rhythm. 25 mm/sec paper speed.
with the timing of many SCD cases in exercising horses, suggesting that large fluctuations in auto- nomic tone may play a role in these cases. Occa- sionally, ECGs obtained during the period immediately preceding SCD reveal VT, R on T complexes, wide VT, or torsade de pointes that degenerate into VF. In most instances, however, the diagnosis is a diagnosis of exclusion at the time of postmortem examination.
Severe bradyarrhythmias and tachyarrhythmias
can cause collapse and SCD in horses. This is re- ported most frequently in young racehorses that are often found dead or collapse and die suddenly. At postmortem examination, there may be myocar- dial lesions or cardiac disease is presumptive, with no other cause of death detected. On occasion, VT is documented in the minutes or hours prior to death. Multifocal myocardial necrosis or fibrosis
Fig. 61. Simultaneous ECG rhythm strips obtained during a high-speed treadmill exercise test demonstrating paroxysmal VT (arrows). Notice the different forms of the ventricular complexes and the short bursts of VT. 25 mm/sec paper speed.
