What an EKG Is (and Isn't)
Core concepts about what an electrocardiogram records, its standard calibration, and its clinical limitations.
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Questions Covered in This Set
10 cards to master
In one sentence, what is an EKG?
A voltage-versus-time graph, recorded from the skin, of the electrical activity generated by heart muscle cells.
Why do EKG and ECG mean the same thing?
'ECG' comes from the English electrocardiogram, 'EKG' from the German Elektrokardiogramm (Einthoven's era). Many hospitals say 'EKG' so it isn't misheard as 'EEG'.
What deflection occurs when depolarization moves TOWARD a positive electrode?
An upward (positive) deflection.
What deflection occurs when depolarization moves AWAY from a positive electrode?
A downward (negative) deflection.
Electrode vs. lead — what's the difference?
An electrode is a sticker on the patient (10 for a standard 12-lead); a lead is a derived viewpoint computed from those electrodes (12 views).
On standard EKG paper, what does one small box equal horizontally?
0.04 seconds (paper speed 25 mm/sec); one large box = 0.20 seconds.
On standard EKG paper, what does one small box equal vertically?
0.1 mV (gain 10 mm/mV); one large box = 0.5 mV.
A QRS spans three small boxes — what is its duration and why does it matter?
3 × 0.04 = 0.12 seconds, the upper limit of normal QRS duration — a meaningful clinical flag.
What is pulseless electrical activity (PEA) and what does it prove?
A cardiac arrest rhythm with organized electrical activity but no pulse — proof that the EKG shows electricity, not mechanical pumping.
Name three things an EKG cannot tell you.
Ejection fraction/valve function (needs echo), it can't rule out coronary disease or MI, and as a ~10-second snapshot it can miss intermittent arrhythmias.
