How does ventricular tachycardia affect cardiac output?

As a medical professional with expertise in cardiology, I can explain how ventricular tachycardia (VT) affects cardiac output. Ventricular tachycardia is a rapid heart rhythm that originates in one of the ventricles (the lower chambers of the heart). When VT occurs, the ventricles beat at a rate of more than 100 beats per minute, which is significantly faster than the normal resting heart rate. This rapid rate can significantly affect cardiac output in several ways: 1. Reduced Filling Time: The ventricles do not have enough time to fill with blood because the heart rate is so fast. This means that with each beat, the ventricles are pumping out less blood than they would under normal conditions. 2. Incoordination with Atrial Contractions: Normally, the atria (the upper chambers of the heart) contract just before the ventricles, helping to push blood into them. In VT, this atrial-ventricular synchrony is lost, which can further reduce the amount of blood that the ventricles receive and subsequently pump out. 3. Diminished Oxygen Supply: The rapid heart rate can also lead to a decrease in the amount of oxygen-rich blood that reaches the body's tissues, as the heart is not efficiently filling and emptying. 4. Potential for Reduced Cardiac Output: If the VT is sustained, it can lead to a state where the cardiac output is significantly reduced. This is because the heart is unable to pump effectively at such a high rate, leading to a condition known as cardiogenic shock. 5. Symptoms and Complications: The reduced cardiac output can cause symptoms such as dizziness, shortness of breath, and fatigue. In severe cases, it can lead to organ damage or failure. In summary, ventricular tachycardia can have a profound impact on cardiac output by reducing the time for ventricular filling, disrupting the normal coordination between atrial and ventricular contractions, and potentially leading to a significant decrease in the amount of blood being circulated throughout the body.

Tachycardia of atrial or ventricular origin reduces stroke volume and cardiac output particularly when the ventricular rate is greater than 160 beats/min. The stroke volume becomes reduced because of decreased ventricular filling time and decreased ventricular filling (preload) at high rates of contraction.