Q classes¶

flowchart TD
    PULSE["electrical pulse"] --> OK{"normal path?"}
    OK -->|yes| N["N — ordinary beat"]
    OK -->|born in ventricles| V["V — ventricular ectopic"]
    OK -->|born early above ventricles| S["S — supraventricular ectopic"]
    OK -->|two pulses collide| F["F — fusion hybrid"]
    OK -->|paced / unreadable| Q["Q — unknown"]

Arrhythmia = beats arriving early, from the wrong chamber, or deformed. Ventricle-born beats are the dangerous ones — runs of them lead toward arrest.

Class	Plain meaning	Danger	Typical share
N	normal beats + harmless wiring detours	none	the bulk
V	born in ventricles, wide bizarre shape	highest — missing one is the worst mistake	small
S	born above ventricles, arrives early	moderate	small
F	normal + ventricular pulse collide	low	tiny
Q	paced or unclassifiable	—	tiny

MIT-BIH holds 48 half-hour patient recordings with ~110,000 expert-labeled beats. Five classes (hospital standard AAMI) keep every class large enough to learn while matching what all papers report.

Next: 03-ml-classification-basics.md