01 — Heart and ECG basics

flowchart LR
    SA["electrical pulse starts"] --> A["atria squeeze\nblood pushed down"]
    A --> V["ventricles squeeze\nblood pushed to body"]
    V --> R["ventricles recover"]

One pulse, one heartbeat. An ECG records that electricity from skin stickers (electrodes): voltage plotted against time. Each bump maps to a squeeze:

Bump	What happens	Shape on trace
P wave	atria squeeze	small bump
QRS complex	ventricles squeeze	tall sharp spike (R is the peak)
T wave	ventricles recover	medium bump

The R peak (tall spike top) is the landmark software finds first; everything else is located relative to it.

• Beat: one heartbeat.
• Lead: one camera angle on the heart electricity (we start with MLII).
• Sampling rate: numbers stored per second (MIT-BIH: 360 Hz, so 1 s = 360 numbers).

Next: 02-arrhythmia-and-aami-classes.md