Sinus Tachycardia in Cats

Changes in heart rate usually involve a reciprocal action of the parasympathetic and sympathetic divisions of the autonomic nervous system (i.e., the automatic impulses of the system that control such actions as breathing and heart rate). Sinus tachycardia (ST) is clinically described as a sinus rhythm (heartbeat) with impulses that arise at a faster-than-normal rate: greater than 240 beats per minute in cats.

Severe tachycardia can compromise cardiac output, as too rapid rates shorten the diastolic filling time, the point in which the chambers of the heart dilate and fill with blood -- which occurs in the space between heart beats. Particularly in diseased hearts, the increased heart rate can fail to compensate for decreased volume, resulting in decreased cardiac output, decreased coronary blood flow and a concurrent increase in oxygen demands. This is the most common benign arrhythmia in cats. It is also the most common rhythm disturbance in postoperative patients. 

Symptoms and Types

• Often no clinical signs because condition is a compensatory response to a variety of stresses
• If associated with primary cardiac disease, weakness, exercise intolerance, or loss of consciousness may be reported
• Pale mucous membranes if associated with anemia or congestive heart failure
• Fever may be present
• Signs of congestive heart failure, such as shortness of breath, cough, and pale mucous membranes may be present when ST is associated with primary cardiac disease

Causes

Physiologic

• Exercise
• Pain
• Restraint
• Excitement
• Anxiety, anger, fright

Pathologic

• Fever
• Congestive heart failure
• Chronic lung disease
• Shock
• Fluid in the chest
• Anemia
• Infection/sepsis
• Low oxygen levels/hypoxia
• Pulmonary blood clot
• Low blood pressure
• Reduced blood volume
• Dehydration
• Tumor

Risk Factors

• Thyroid medications
• Primary cardiac diseases
• Inflammation
• Pregnancy