Increased Heart Rate Due to Premature Contractions in Dogs

Ventricular tachycardia (VT) refers to a potentially life-threatning condition of abnormally fast heart beat (arrhythmia). VT is rapid, erratic heart beats, caused by abnormal electrical impulses that are generated somewhere within the ventricles of the heart. 

Ventricular refers to the ventricles of the heart; “tachycardia” is the medical term for rapid heart rate. Hence, ventricular tachycardia is a rapid heart beat that originates in one of the lower chambers (the ventricles) of the heart. To be classified as tachycardia, the heart rate is usually at least 100 beats per minute. Ventricular tachycardia is a fast but regular rhythm. The condition can deteriorate into fast and irregular rhythm known as ventricular fibrillation (muscular twitching involving individual muscle fibers acting without coordination). Asystole – a sudden lack of electrical activity in the heart – may result as a consquence and sudden death may occur.

The heart of a dog is made up of two upper chambers known as atria (singular: atrium) and two bottom chambers known as the ventricles. Heart valves are located between the right atrium and the right ventricle (tricuspid valve); between the left atrium and the left ventricle (mitral valve); from the right ventricle to the main pulmonary (lung) artery (pulmonary valve); and from the left ventricle to the aorta (the main artery of the body; valve is the aortic valve).

The heart needs to function in a coordinated fashion to pump the blood to the lungs and the body. Sinus or sinoatrial (SA) node starts electrical impulse which causes atria to contract, pumping blood into ventricles. Electrical impulse moves through the atrioventricular (AV) node and into the ventricles, causing the ventricles to contract and to pump blood to the lungs (right ventricle) and the body (left ventricle). Ventricular tachycardia is related to abnormal behavior in the ventricles.

Ventricular tachycardia  may occur in structurally normal hearts, as hereditary arrhythmias, or may be a consequence of myocardial abnormalities associated with cardiomyopathy (heart muscle disease), significant valvular disease, or myocarditis (heart muscle inflammation).

Clinically affected dogs present frequently with syncope, weak femoral pulses, pale mucous membranes, panting, weakness, exercise intolerance, congestive heart failure (CHF), sudden death and tachycardia audible on auscultation. 

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