Flashcards in Clinical Deck (43):
What is the P wave?
What is the PR interval? Normal interval?
start of atrial depolarization to start of ventricular depolarization; .12-.20 seconds (3-5 small boxes)
What is the QRS complex? Normal duration?
ventricular depolarization; 0.05-0.10 seconds (1-3 small boxes)
What is the ST segment?
end of QRS complex to beginning of T wave; plateau phase 2 for ventricles (rapid ejection phase)
What do ST depressions represent?
What do ST elevations represent?
subepicardial or transmural injury/ischemia
What is the T wave? What do inverted T waves and tall upright T waves represent?
inverted T wave = ischemia
tall upright T wave = hyperkalemia
What is QT duration?
reflects time of ventricular activity (both depolarization and repolarization)
What is the PR segment?
reflects time delay between atrial depolarization and ventricular depolarization
What does sinus tachycardia look like?
sinus rhythm (P wave before every QRS) but HR is above 100bpm
What does premature atrial contraction (PACs) look like?
QRS complex is the same throughout but there will be occasional extra beats w/ abnormal P wave and then a lengthy pause afterwards
Physiology of PACs
atrial depolarization somewhere other than SA node (closer to AV node b/c P wave is closer to QRS); long pause b/c SA node is depolarized when it would normally fire
What do premature ventricular contractions (PVCs) look like?
widened QRS complex; too many in a row can turn into Vtach
Physiology of PVCs
ventricular depolarization somewhere other than His/Purkinje system; myocardial muscle has slower conduction rate (widened QRS)
What does atrial fibrillation (Afib) look like?
irregularly irregular rhythm; variable rate w/ no P waves present; R to R interval is all over the place
Physiology of Afib
multiple foci depolarizing in atria; can also have rapid ventricular response (tachycardia)
PVCs coming from different regions of ventricular muscle; each will look different
What does ventricular tachycardia (Vtach) look like?
extremely high HR w/ widened QRS
What does non-sustained monomorphic ventricular tachycardia look like?
Vtach with occasionally normal beats; all runs of Vtach look the same b/c they come from same loci
What does supraventricular tachycardia (SVT) look like?
fast HR w/ narrow QRS (not Vtach) and R to R interval will be the same (not Afib)
What does 1st degree AV block look like?
more than 1 large box between P wave and QRS complex
What causes a deflection on an ECG?
when part of cardiac tissue is at a different membrane potential than the rest of the heart; will be at isoelectric point when all cardiac tissue has same membrane potential
What are inferior leads?
II, III, aVF
What are septal leads?
V1 and V2
What are anterior leads?
V2, V3, and V4
What are lateral leads?
V4, V5, V6, I, and aVL
What is normal axis?
between -30 and +90 -> current moves from RA to apex (down and to the left)
How would you determine LAD? What does it mean physiologically?
left axis deviation = lead I upright and aVF inverted (up and to the left); generally means left ventricular hypertrophy
How would you determine RAD? What does it mean physiologically?
right axis deviation = lead I inverted and aVF upright (down and to the right); generally means right ventricular hypertrophy
What do you call inverted I and aVF?
extreme right axis deviation
What is the J point?
first point of the ST segment (junction between QRS complex and ST segment)
Describe the difference between unstable angina (UA) and NSTEMI
both have ST depressions, T wave inversion, and chest pain
UA or NSTE acute coronary syndrome (ACS) has normal cardiac enzymes
NSTEMI has elevated cardiac enzymes
What indicates a STEMI is occurring?
ST elevation of 2mm (2 boxes) or > at J point
ST elevation of 1.5mm or > in women or 1mm or > in 2 or more contiguous chest or limb leads
What appears on ECG if there is an infarction?
Q waves -> dead tissue lacks depolarization
What appears on ECG if there is an injury?
ST segment shifts -> deficient blood supply means there is an inability to fully polarize
What appears on ECG if there is ischemia?
T wave changes -> impaired repolarization due to deficient blood supply
Where would you see an anterior MI? What artery is involved?
V1-V4; LAD or anterior interventricular A.
Where would you see an inferior MI? What artery is involved?
II, III, aVF; right coronary A.
Where would you see a lateral MI? What artery is involved?
I, aVL, V5-V6; circumflex A. (also diagonal A. of LAD)
Where would you see a posterior MI? What artery is involved?
V1-V3; posterior descending A/posterior interventricular A.
How would you actually determine a posterior MI had occurred?
Pt would have ST depressions in V2-V3 b/c leads are on anterior side of heart (would mirror the MI); flip the ECG upside down to see elevations
What might you also see with an MI on ECG besides ST elevations?
ST depressions -> reciprocal changes in different leads