Page 176 - Problem-Based Feline Medicine

168 PART 3 CAT WITH SIGNS OF HEART DISEASE

Recording several leads, especially chest leads, will
DISEASES CAUSING BRADYCARDIA
facilitate identification of P waves.

SINUS BRADYCARDIA* Treatment

Classical signs Treat the underlying disease.
● Heart rate less than 120 beats per minute. The response to atropine administration should be
● Pulse is regular. determined to assess normal sinus node function.
● Weakness.
● Collapse. Prognosis

The prognosis depends on the underlying disease.
Pathogenesis
ATRIAL STANDSTILL*
This arrhythmia originates from the sino-atrial node,
the normal pacemaker of the heart. It is usually indica- Classical signs
tive of severe underlying cardiac disease or second-
● Weakness.
ary to extracardiac disease.
● Collapse.
Extracardiac causes most commonly associated with ● Lethargy.
this arrhythmia are:
● Respiratory disease.
● Intracranial disease. Pathogenesis
● Electrolyte disturbances (hyper or hypokalemia).
The arrhythmia can result from atrial cardiomyopathy.
● Metabolic disturbances (acidosis, hypoglycemia).
● Hypothermia and hypoxia. The arrhythmia can occur in long-standing cardiac
● Overdose of beta-blockers or calcium channel disease, more commonly seen in the dilated form.
blockers, anesthetic agent or digitalis.
The arrhythmia can result from hyperkalemia,
primarily because of feline urethral obstruction
Clinical signs syndrome.

If the heart rate is less than 100 beats per minute, weak- A serum potassium greater than 8.5 mEq/L (mmol/L)
ness, collapse and lethargy may be seen. results in disappearance of P waves and results in atrial
standstill.
In the majority of patients, clinical signs are related to
the underlying disease.
Clinical signs
Diagnosis
Signs may be related to the underlying disease.
The heart rate is lower then 120 bpm.
Weakness, lethargy and collapse are most commonly
There is a P wave for every QRS complex. seen.
The QRS complex morphology is normal.
The atropine response test is normal (give 0.04 mg/kg IV Diagnosis
while recording rhythm strip, if no response in 2 minutes
The heart rate is slower than 120 bpm (Figure 10.6).
repeat dose).
There are no P waves in any lead.
Differential diagnosis The ventricular rhythm is regular.

Sinus bradycardia may be diagnosed as a junctional escape The QRS complex morphology may be normal or
rhythm in cases where P waves are isoelectric. increased in duration and bizarre in morphology.