Cardiovascular System - Electrical Activity and ECG

These flashcards cover the electrical activity of the heart, including pacemaker function, action potential phases, excitation-contraction coupling, ECG wave interpretations, electrolyte impacts, and various heart arrhythmias.

How are cardiac muscle cells interconnected, allowing electrical impulses to flow from cell to cell?

They are interconnected by gap junctions called intercalated discs.

What is the term for the area of the heart that contracts as a single unit from one stimulation event?

A myocardium or functional syncytium.

What structure electrically separates the atria and the ventricles?

The fibrous skeleton.

Why is the sinoatrial node (SA node) considered the pacemaker of the heart?

It exhibits the greatest degree of self-excitation and has the highest inherent discharge rate.

What are the pathways that conduct impulses from the SA node to the AV node?

Internodal Pathways and Bachmanns bundles (Anterior, middle, and posterior pathways).

What is the specific threshold voltage for nodal fibers to open their $Ca^{2+}$ and $Na^+$ channels?

$-40$ millivolts.

What causes the self-excitation of sinus nodal fibers?

An inherent leakiness to $Na^+$ ions which causes the membrane potential to rise naturally.

In a cardiac pacemaker cell monophasic action potential, what ions are responsible for Phase 0 and Phase 3?

Phase 0 is caused by $Ca^{2+}$ influx, and Phase 3 is caused by $K^+$ efflux.

What is the difference between positive chronotropic and positive inotropic effects?

Positive chronotropic effects increase the rate of SA node discharge (heart rate), while positive inotropic effects increase the force of cardiac contraction.

Which sympathetic receptors are primarily used during heart failure because $\beta_1$ receptors become down-regulated?

$\beta_2$ receptors.

What is the resting membrane potential range for ventricular fibers between discharges?

$-85$ to $-90$ millivolts.

How does the duration of the plateau phase in cardiac muscle compare to skeletal muscle?

The cardiac plateau phase is $3$ to $15$ times the duration of the plateau phase in skeletal muscle.

Which specific calcium channels remain open longer to contribute to the extended plateau phase in cardiac muscle?

L-TYPE calcium-sodium channels.

How does the onset of an action potential affect the cardiac muscle's permeability to potassium?

It decreases permeability by about $5$ fold, preventing early recovery by decreasing potassium outflux.

What is the name of the calcium release channel on the sarcoplasmic reticulum (SR) involved in excitation-contraction coupling?

Ryanodine Receptor type 2 (RYR2).

How do the T-tubules in cardiac muscle differ from those in skeletal muscle?

In cardiac muscle, T-tubule diameter is $5$ times larger and the volume is $25$ times greater than in skeletal muscle.

What do the P wave and the QRS wave represent on an ECG?

The P wave represents atrial depolarization, and the QRS wave represents ventricular depolarization.

What electrical event is represented by the T wave on an ECG?

Ventricular repolarization.

How is hyperkalaemia ($> 5.2$ $mmol/L$) characterized on an ECG trace?

Tall "tented" T waves, P wave flattening, PR prolongation, and QRS widening.

What are the three bipolar limb leads and what do they record?

Lead I (right arm to left arm), Lead II (right arm to left leg), and Lead III (left arm to left leg).

Match the heart sounds "Lub" and "Dub" to their corresponding electrical events on the ECG.

"Lub" occurs after the QRS wave (AV valves close); "Dub" occurs at the beginning of the T wave (SL valves close).

Define bradycardia and tachycardia as heart rhythms at rest.

Bradycardia is a slow heart rate below $60$ $bpm$; tachycardia is a fast heart rate above $100$ $bpm$.

What is the difference between a flutter and fibrillation?

Flutter involves extremely fast ($200$ to $300$ $bpm$) but coordinated contractions, while fibrillation involves uncoordinated pumping.

Why is ventricular fibrillation considered fatal without immediate intervention?

The ventricles cannot pump blood, leading to sudden death, moving from ventricular tachycardia through fibrillation to asystole.

Describe the characteristics of a third-degree AV node block.

No electrical stimulation gets through from the atria to the ventricles; a pacemaker in the Purkinje fibers takes over at a slow rate of $20$ to $40$ $bpm$.