SVV stands for "Systolic time variation," a physiological index used to evaluate circulatory dynamics and cardiac function. It quantifies the variability in the time interval between the R wave on an electrocardiogram (ECG) and the subsequent systolic arterial pressure waveform. SVV is commonly used as a parameter to assess the intravascular volume status and guide fluid management in critically ill patients.
When measured invasively, SVV is determined by analyzing the arterial blood pressure waveform and the ECG signal. With each heartbeat, the R wave on the ECG represents the electrical depolarization of the heart, while the arterial pressure waveform corresponds to the contraction and relaxation of the heart. By analyzing the time difference between these two events, SVV can provide insight into cardiac performance and preload responsiveness.
Clinicians use SVV to optimize fluid therapy in patients undergoing surgery, those with sepsis, and other conditions where intense hemodynamic monitoring is necessary. A decrease in SVV suggests that the patient is most likely adequately hydrated and preload optimized, while an increase in SVV indicates inadequate preload or fluid responsiveness. By monitoring SVV, healthcare professionals can make informed decisions regarding fluid administration, avoiding both overhydration and volume depletion.
In conclusion, SVV is an index derived from the relationship between the arterial pressure waveform and the electrical activity of the heart. It is utilized as a measure of intravascular volume status and guide to fluid management in critically ill patients.