Channel my Inner Ion
Electrogenic transporters include the Na+-Ca2+ exchange, active Ca2+ pump, and this pump to maintain a famous concentration gradient
What is the Na+-K+ (ATPase) pump?
*Since this pushes sodium out, the Na+-Ca2+ exchange pushes calcium out for more sodium. This is how digoxin also forces more calcium in by inhibiting the pump!
The plateau phase of action potentials can dictate certain arrhythmias and is characteristic to this cell type
What is nonpacemaker/atrial/ventricular myocardial cell?
*Plateau is phase 2, and initial repolarization (phase 1) is also unique to this compared to SA cell
The QRS complex represents this cardiac conduction action
What is ventricular depolarization?
*Atrial repolarization technically happens at the same time, but it does not really contribute to the QRS shape
By hardwiring cardiac cells with this unique cell structure, heart muscle can synchronize contractions at the risk of triggering arrhythmias with rogue depolarizations
What is an intercalated disc (gap junction okay)?
*Intercalated disc includes gap junctions AND desmosomes
This EKG measurement represents the entirety of systole
What is the QT interval?
*From ventricular depolarization (Start of QRS) to full repolarization (End of T wave)! Reduced ejection occurs during the T wave
Occlusion of a channel pore, chemical ligation, conformation changes of the channel, increased [Ca2+], and hyperpolarization all lead to this ion channel state
What is inactivated state?
*NOT the closed state, but it does minimize voltage changes. The faster you can switch between these states increases use dependence, critical for Class I antiarrhythmics!
SA nodal cells depend on this ion to successfully perform the upstroke/depolarization
What is calcium?
*Sodium is for nonpacemakers cells, but they both perform upstroke (phase 0) in their respective cells
This EKG wave represents ventricular repolarization
What is the T wave?
*Near the end of the T wave is isovolumetric relaxation and thus the jugular venous v wave!
Abnormal automaticity means all cardiac cells show excessive repetition of this action potential phase
What is phase 4/depolarization?
*Abnormal due to being in non-pacemaker cells, which can be triggered by acidosis, hypoxia, stretch receptors, hypokalemia, etc.
The first phase of diastole is this phase in the cardiac cycle which is slightly after a T wave ends
What is isovolumetric relaxation?
*You should hear S2, and remember this is when LV pressure > LA pressure
These receptors maintain intracellular calcium homeostasis with the sarcoplasmic reticulum
What is the ryanodine receptor?
*A mutation here can lead to a catecholaminergic VT alongside a calsequestrin 2 mutation that may release too much calcium. Both are autosomal dominant
To ensure both atria have enough time to contract and fill ventricles before those contract, conduction velocity is slowest in this electrical tissue
What is AV node?
*The fastest is Purkinje fibers to let all myocytes depolarize quickly and uniformly!
For normal EKG electrical conductance, the QRS axis should have a positive QRS complex in these two leads
What are leads I and aVF?
*This means the net vector is going down and to the left in the heart! Lead II can replace aVF in some cases, but better to use aVF
An increase of incompletely repolarized action potentials of these two action potential phases indicates triggered early afterdepolarizations
What are phases 2 and 3?
*Phase 2 may have prolonged calcium channels and phase 3 may open sodium channels, or both can have potassium channel defects
Isovolumetric contraction becomes systolic ejection once ventricular pressure exceeds the pressure of this region
What is aorta/aortic valve?
*This occurs right around the R wave
This ion channel draws sodium (and potassium) in via HCN to slowly depolarize the cell, but it is only triggered with hyperpolarization
What is the funny/pacemaker channel?
*That's what makes it funny! This occurs in phase 4 of the SA node-like cells to generate sinus node automaticity!
The start of ventricular depolarization occurs on the lower left portion of this part of the heart
What is the interventricular septum?
*Specifically the left bundle branch! It goes from left ventricles and then right ventricles to produce the QRS complex!
The Purkinje fibers quickly conduct to this part of the heart, the final points of the conduction cycle
What is the ventricular myocardium?
*Remember it has to spread to the walls and ultimately into its endocardium to actually contract!
In cells with two parallel conduction pathways, if one gets blocked and unblocked such that the other can travel in a loop, this general arrhythmia phenomenon has occurred
What is reentry?
*WPW, AVNRT all work under this mechanism of self-perpetuation
Active filling of the ventricles is represented with this EKG wave and finishes diastole
What is the P wave?
*It initiates the atrial kick, which you hear as S4 right after P wave ends!
By disrupting sodium channels during repolarization in this channelopathy, you get differing refractory periods that can lead to reentry circuits that lead to PVCs and ultimately polymorphic VT
What is Brugada Syndrome?
*Loss of SCN5A or SCN10A sodium channel function that creates the "shark-fin/coved" (Type 1) or "saddleback" (Type 2) ST elevation. The opposite of this condition is long QT3 (gain of SCN5A)
Phases 3 and 4 of cardiac cells represents this timeframe in the action potential cycle
What is the relative refractory period?
*Phases 1 and 2 are the absolute refractory period!
The peak of the QRS complex is when the mitral valve closes, which means this jugular venous wave/descent also appears at the same time
What is the c wave?
*Mitral and tricuspid valves effectively close at the same time. Since QRS shows ventricular depolarization (thus isovolumetric contraction), this must be the c wave!
This arrhythmic phenomenon occurs with high intracellular [Ca2+] that occurs after repolarization but before the expected phase 0 depolarization
What is delayed afterdepolarization?
*Digoxin/digitalis toxicity can induce this, leading to atrial or ventricular tachycardia
The flat part after the T wave is this cardiac cycle stage with reduced/no ventricular filling due to equal atrial and ventricular pressures
What is diastasis?
*If diastole is shortened, atrial contraction (P wave) leads to significant ventricular filling in a process called atrial kick (AKA your S4!)