arrythmia

Question 1

What is the most efficient rhythm for the heart, and how do arrhythmias affect cardiac function?

Answer 1

The heart functions most efficiently in sinus rhythm. Any arrhythmia compromises cardiac function by disrupting the normal sequence of heart muscle contractions.

Question 2

Why is an understanding of the ionic basis of the cardiac action potential important in arrhythmia treatment?

Answer 2

Antiarrhythmic drugs work predominantly by altering the function of transmembrane ion channels, affecting the movement of ions across heart cell membranes and thus the cardiac action potential.

Question 3

What is the principle of the Vaughan–Williams classification?

Answer 3

The Vaughan–Williams classification groups antiarrhythmic drugs based on their action on specific transmembrane ion channels involved in cardiac action potentials.

Question 4

What are the risks associated with antiarrhythmic drugs?

Answer 4

Antiarrhythmic drugs may be proarrhythmic in certain circumstances, potentially causing or worsening arrhythmias.

Question 5

What non-pharmacological treatments are increasing in use for arrhythmias?

Answer 5

Catheter ablation and device therapy (e.g., pacemakers, ICDs) are becoming more common for arrhythmia treatment, offering alternatives when drugs have limited efficacy or cause significant toxicity.

Question 6

Why is atrial fibrillation (AF) significant, and what should all AF patients undergo?

Answer 6

AF is the most common arrhythmia and increases the risk of thromboembolic stroke. All AF patients should undergo an assessment of their stroke risk.

Question 7

Describe the resting membrane potential in cardiac myocytes.

Answer 7

The resting membrane potential of −60 to −90 mV in cardiac myocytes is due to high intracellular potassium (K+) concentration, maintained by the Na+-K+-ATPase pump and K+ efflux through selective channels.

Question 8

What triggers the pacemaker potential in certain heart cells?

Answer 8

The pacemaker potential is triggered by a gradual depolarisation during diastole, influenced by a reduction in K+ current, a reduction in acetylcholine-activated K+ current, and an increase in inward Na+ and K+ current (I f).

Question 9

How does the autonomic nervous system influence heart rate?

Answer 9

The sympathetic nervous system increases heart rate by increasing I f current via β1-adrenoreceptors and cAMP. The parasympathetic nervous system decreases heart rate by reducing I f current and increasing outward K+ current (I KAch).

Question 10

What initiates Phase 0 of the cardiac action potential?

Answer 10

The rapid influx of sodium (Na+) ions into the heart cell through “fast” Na+ channels.

Question 11

What marks the beginning of Phase 1 (Initial Repolarisation) of the cardiac action potential?

Answer 11

Closure of the fast Na+ channels and the efflux of potassium (K+) ions through Ito channels.

Question 12

What characterizes the Plateau Phase (Phase 2) of the cardiac action potential?

Answer 12

The balanced influx of calcium (Ca2+) ions and efflux of K+ ions, maintaining the membrane potential near 0 mV.

Question 13

What occurs during Phase 3 (Repolarisation) of the cardiac action potential?

Answer 13

Decreased calcium influx and predominance of potassium efflux, returning the cell to its resting membrane potential.

Question 14

What maintains the cell’s resting state in Phase 4 of the cardiac action potential?

Answer 14

The cell remains at a stable, negative resting potential, ready for the next action potential.

Question 15

Where does the heartbeat initiation occur in the heart?

Answer 15

In the sinoatrial (SA) node, where pacemaker cells generate an electrical impulse.

Question 16

What is the role of the annulus fibrosus in cardiac conduction?

Answer 16

It electrically insulates the atria from the ventricles, ensuring orderly contraction.

Question 17

What does the QRS complex on an ECG represent?

Answer 17

Ventricular depolarisation (contraction), reflecting rapid conduction through the His-Purkinje system.

Question 18

What does the P wave on an ECG represent?

Answer 18

Atrial depolarisation (contraction).

Question 19

What is indicated by the PR interval on an ECG?

Answer 19

The conduction time through the AV node, from atrial to ventricular depolarisation.

Question 20

What does the T wave on an ECG represent?

Answer 20

Ventricular repolarisation (relaxation).

Question 21

What is the significance of the QT interval on an ECG?

Answer 21

It represents the total time for ventricular depolarisation and repolarisation.

Question 22

What is abnormal automaticity in the context of cardiac arrhythmias?

Answer 22

Abnormal automaticity refers to the inappropriate generation of electrical impulses by cardiac cells outside the specialized conduction system or by an accelerated pace within it, disrupting normal heart rhythm.

Question 23

What factors determine the rate of firing of a pacemaker cell?

Answer 23

The rate of firing is determined by the maximum diastolic potential, the slope of diastolic depolarization, and the threshold potential required to generate a new action potential.

Question 24

What are early afterdepolarizations (EADs) and their association with cardiac arrhythmias?

Answer 24

EADs are unexpected electrical changes during or immediately after the repolarization phase of the cardiac action potential, associated with long QT syndromes and can lead to arrhythmias like Torsade de pointes.

Question 25

What causes delayed afterdepolarizations (DADs) and their potential effect on heart rhythm?

Answer 25

DADs are caused by spontaneous calcium release from the sarcoplasmic reticulum, leading to potential ectopic beats or tachycardia, especially under conditions like heart failure or digitalis toxicity.

Question 26

What is re-entry and its significance in arrhythmogenesis?

Answer 26

Re-entry is a mechanism where an electrical impulse circulates within a heart pathway, continuously reactivating it, leading to sustained arrhythmias due to specific conditions like unidirectional block and slow conduction.

Question 27

What electrophysiological conditions must be met for re-entry to occur?

Answer 27

Conditions include a non-conducting central obstacle, a unidirectional conduction block, slow enough conduction in the alternate pathway, and excitable tissue along the circuit.

Question 28

How do Class I antiarrhythmic drugs affect re-entry circuits?

Answer 28

Class I drugs block sodium channels, reducing the speed of the activation wavefront, which can prevent the continuation of a re-entry circuit by inhibiting conduction in diseased myocardium.

Question 29

What is the mechanism by which Class III antiarrhythmic drugs prevent re-entrant arrhythmias?

Answer 29

Class III drugs prolong the cardiac action potential duration and refractory period, preventing previously activated cells from reactivating when the re-entrant wavefront returns, thereby terminating the arrhythmia.

Question 30

What does a sudden onset of palpitations suggest compared to a gradual onset?

Answer 30

Sudden onset palpitations are indicative of an arrhythmia, whereas gradual onset palpitations may be due to heightened awareness of sinus tachycardia.