Arrhythmia Ablation

ECG of the Month

“…Sinus bradycardia is defined as a regular rhythm < 60 beats/min in awake dogs [3][4][5] ; healthy dogs may have lower heart rates during sleep. In clinical practice, SB is an uncommon rhythm disturbance and generally is secondary to drug overdose in anesthetized dogs.…”

“…3 In conscious dogs, SB can be associated with physiologic and pathological conditions, such as hypothermia, hypoxia, hyperkalemia, or any increase in vagal tone (attributable to vagal reflexes, intestinal obstruction, urethral obstruction, or intracranial mass). [3][4][5] Other causes known to decrease heart rate are related to administra- tion of drugs, such as digoxin, β-adrenoceptor antagonists, calcium channel blockers, or lidocaine. In dogs with marked SB secondary to vagotonia (vagal maneuvers), a sinus arrhythmia may be present with normal PQRS-T intervals and variation in P-P intervals.…”

“…When serum potassium concentration exceeds 5.5 mEq/L, ECG recordings may reveal SB, tall and peaked T waves, low-amplitude or absent P waves, low-amplitude R waves, and prolonged PR and QRS intervals. [3][4][5] The ECG changes generally worsen with increasing serum potassium concentration, but there may be coexistent acid-base and electrolyte imbalances, which could alter or mask ECG signs of hyperkalemia. The dog of this report did not have any detectable electrolyte imbalance, and SB as a result of hyperkalemia was ruled out.…”

“…3,4 The most frequent clinical sign of sick sinus syndrome is sinus arrest or sinoatrial block (48.5% of dogs with sick sinus syndrome). 5 Affected dogs also commonly have periods of sustained tachyarrhythmias coexisting with bradyarrhythmia. 3,5 For the dog of this report, sick sinus syndrome was ruled out on the basis of the Holter monitoring findings.…”

“…5 Affected dogs also commonly have periods of sustained tachyarrhythmias coexisting with bradyarrhythmia. 3,5 For the dog of this report, sick sinus syndrome was ruled out on the basis of the Holter monitoring findings.…”