In which condition is a saw tooth baseline observed?

A saw tooth baseline is characteristic of atrial flutter, specifically referred to as "sawtooth" or "F-waves." This phenomenon occurs due to the rapid reentrant circuits in the atria, creating a distinctive pattern on an electrocardiogram (ECG). The F-waves generally present as regular, oscillating waves that resemble the teeth of a saw, typically occurring at a rate of around 250 to 350 beats per minute.

In conditions like ventricular fibrillation, the ECG shows chaotic, irregular electrical activity without any organized waveforms. Sinus arrhythmia exhibits variability in the heart rate that correlates with breathing but lacks any specific waveform pattern like that of atrial flutter. PAC, or premature atrial contraction, may present with early premature beats but does not produce the characteristic sawtooth pattern indicative of atrial flutter.

Thus, the distinctive sawtooth pattern seen in atrial flutter is a reliable way to identify this particular arrhythmia on an ECG.