Heart sounds, murmurs and ECG
What the stethoscope and the ECG show: the four heart sounds and S2 splitting, murmurs and the dynamic manoeuvres that change them, HOCM versus aortic stenosis, then the ventricular and pacemaker action potentials behind the ECG waves and intervals.
5:26S2 splitting and heart sounds S1–S4, explained
Heart sounds are valves closing. Read S2 splitting with two questions: which valve is late, and does the gap move with breathing?
5:15Heart murmurs and dynamic manoeuvres, from preload and afterload
A murmur follows the flow: manoeuvres that change preload or afterload change how much blood crosses the lesion. Hypertrophic obstructive cardiomyopathy is the exception that flips the rule.
5:31HOCM vs aortic stenosis murmur: telling them apart at the bedside
Both murmurs are harsh and systolic. The difference is the obstruction: a fixed valve in aortic stenosis, a dynamic muscle and mitral leaflet in HOCM. The manoeuvres follow from that.
5:15Ventricular action potential: phases 0 to 4 and their ion currents
A ventricular muscle cell takes about a quarter of a second to fire. Match each phase to its ion current, then to the antiarrhythmic class that acts on it.
5:17SA node pacemaker potential: phase 4 sets the heart rate
Sinoatrial nodal cells have no stable resting potential. Heart rate is the slope of phase 4, and the vagus and sympathetic nerves simply move that slope.
5:29ECG waves and intervals: what P, PR, QRS, ST and QT mean
Each ECG wave and interval maps to an electrical event in the heart. Read the gaps and you can tell where a conduction delay sits.