A

a wave
The atrial pressure upstroke from atrial contraction; absent in atrial fibrillation, giant (cannon) in AV dissociation.
ACT (activated clotting time)
The bedside test used to monitor unfractionated heparin during a procedure; a target ACT confirms adequate anticoagulation.
Afterload
The resistance the ventricle must overcome to eject blood, largely set by systemic vascular resistance. Higher afterload lowers stroke volume.
ALARA
The radiation-safety principle "As Low As Reasonably Achievable," applied through time, distance, and shielding. See radiation safety.
Allen test
A check of the ulnar (collateral) circulation to the hand before radial artery access.
Aortic stenosis
Narrowing of the aortic valve; graded by valve area, mean gradient, and jet velocity.
Atrial fibrillation
An irregularly irregular rhythm with no discernible P waves; see rhythm interpretation.

B

Bundle of His
Part of the conduction system carrying the impulse from the AV node into the ventricular septum.

C

Cardiac index
Cardiac output divided by body surface area (normal 2.5–4.0 L/min/m²). Full guide: cardiac index.
Cardiac output
Blood pumped per minute (heart rate × stroke volume), normally 4–8 L/min. See cardiac output.
Cardiac tamponade
Pericardial fluid compressing the heart; a blunted y descent and pulsus paradoxus are classic. See tamponade hemodynamics.
Contrast-induced nephropathy
Kidney injury within 48–72 hours of iodinated contrast; prevented with hydration and minimal volume.
Coronary dominance
Defined by which artery gives the posterior descending artery — the RCA in ~85% (right dominant). See coronary anatomy.

D

DAPT
Dual antiplatelet therapy — aspirin plus a P2Y12 inhibitor, standard after stenting. See cath lab medications.
Dicrotic notch
The small notch on an arterial pressure tracing marking closure of the aortic (or pulmonic) valve.

E

Ejection fraction
The percentage of the filled ventricle ejected per beat (normal 50–70%). See ejection fraction.

F

FFR (fractional flow reserve)
A pressure-wire measurement of the physiological significance of a coronary stenosis; ≤0.80 is flow-limiting.
Fick principle
Cardiac output = oxygen consumption ÷ arteriovenous oxygen difference. Try the Fick calculator.

G

Gorlin equation
The formula relating valve area to flow and gradient; see the aortic valve area calculator.
Guidewire
The wire that provides a rail for catheters and devices; 0.035-inch for diagnostic work, 0.014-inch for coronary. See equipment.

H

Heparin
An anticoagulant monitored by ACT and reversed by protamine. See medications.

I

IABP (intra-aortic balloon pump)
A counterpulsation support device that inflates in diastole and deflates in systole. Full guide: IABP.
Introducer sheath
A valved tube placed in the artery that maintains access and allows catheter exchange.
IVUS (intravascular ultrasound)
Ultrasound imaging from inside the vessel to size stents and assess plaque.

M

MAP (mean arterial pressure)
The average arterial pressure over the cardiac cycle (DBP + ⅓ pulse pressure). See MAP.

N

No-reflow
Impaired microvascular perfusion despite a patent epicardial artery after PCI.

P

PCWP (wedge pressure)
Pulmonary capillary wedge pressure, which approximates left atrial pressure (normal 4–12 mmHg).
Preload
The degree of ventricular filling before contraction; by Frank-Starling, more stretch means a stronger beat.
Protamine
The reversal agent for heparin, dosed at about 1 mg per 100 units of heparin.
PVR (pulmonary vascular resistance)
Resistance of the pulmonary circulation ((mean PAP − PCWP) ÷ CO × 80); normal under ~250 dynes·s·cm⁻⁵. See vascular resistance.

Q

QTc
The QT interval corrected for heart rate; over 500 ms raises torsades risk. See QT interval.

S

Shock index
Heart rate ÷ systolic blood pressure, an early marker of instability. See shock index.
Square-root sign
A dip-and-plateau ventricular diastolic waveform seen in constriction and restriction.
STEMI
ST-elevation myocardial infarction — ST elevation in contiguous leads. See STEMI interpretation.
Stroke volume
Blood ejected per beat (normal 60–100 mL); end-diastolic minus end-systolic volume. See stroke volume.
SVR (systemic vascular resistance)
The afterload of the systemic circulation ((MAP − CVP) ÷ CO × 80). Full guide: SVR.

T

Thermodilution
A cardiac-output method using a cold-saline temperature curve in the pulmonary artery; unreliable in low output, TR, or shunts.

V

v wave
The atrial pressure wave from filling against a closed AV valve; a giant v wave suggests mitral regurgitation.
Vasovagal reaction
A reflex of bradycardia and hypotension, treated with atropine and IV fluids.

W

Wenckebach (Mobitz I)
Second-degree AV block with progressive PR lengthening until a beat drops.
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