PR interval

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Schematic representation of normal ECG

In case a Q wave was measured with an ECG, the PR interval is also commonly named "PQ interval" instead.

Interpretation

Variations in the PR interval can be associated with certain medical conditions:

Duration
- A long PR interval (of over 200 ms) may indicate a first degree heart block.^[1] Prolongation can be associated with hypokalemia, acute rheumatic fever, ^[2] or carditis associated with Lyme disease. ^[3]

- A variable PR interval may indicate other types of heart block.
PR segment depression may indicate atrial injury^{[citation needed]} or pericarditis.^[4]
Variable morphologies of P waves in a single ECG lead is suggestive of an ectopic pacemaker rhythm such as wandering pacemaker or multifocal atrial tachycardia

Volumes	Stroke volume = End-diastolic volume – End-systolic volume Cardiac output = Heart rate × Stroke volume Afterload Preload Frank–Starling law of the heart Cardiac function curve Venous return curve Aortic valve area calculation Ejection fraction Cardiac index

Dimensions	Fractional shortening = (End-diastolic dimension – End-systolic dimension) / End-diastolic dimension

Interaction diagrams	Cardiac cycle Wiggers diagram Pressure volume diagram

Tropism	Chronotropic (Heart rate) Dromotropic (Conduction velocity) Inotropic (Contractility) Bathmotropic (Excitability) Lusitropic (Relaxation)

Conduction system / Cardiac electrophysiology	Cardiac action potential Atrial action potential Ventricular action potential Effective refractory period Pacemaker potential EKG P wave PR interval QRS complex QT interval ST segment T wave U wave Hexaxial reference system

Chamber pressure	Central venous pressure/right atrial pressure → Right ventricular pressure → Pulmonary artery pressure → Pulmonary wedge pressure/left atrial pressure → Left ventricular pressure → Aortic pressure

Other	Ventricular remodeling

Vascular system/
Hemodynamics

Blood flow	Compliance Vascular resistance Total peripheral resistance Pulse Perfusion

Blood pressure	Pulse pressure Systolic Diastolic Mean arterial pressure Jugular venous pressure Portal venous pressure

Regulation of BP	Baroreflex Kinin–kallikrein system Renin–angiotensin system Vasoconstrictors/Vasodilators Autoregulation Myogenic mechanism Tubuloglomerular feedback Cerebral autoregulation Paraganglia Aortic body Carotid body Glomus cell

anat/phys/devp

noco/cong/tumr, sysi/epon, injr

proc, drug (C1A/1B/1C/1D), blte

anat (a:h/u/t/a/l,v:h/u/t/a/l)/phys/devp/cell/prot

noco/syva/cong/lyvd/tumr, sysi/epon, injr

proc, drug (C2s+n/3/4/5/7/8/9)

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