Dysrhythmias Flashcards

Question

What are the characteristic ECG features of a 3rd degree AV block?

Answer 1

* Complete block of electrical continuity between the atria and the ventricles (that is, the P waves do not have associated QRS complexes) * Produces a ventricular escape rhythm * inherent rhythm of 15 – 40 bpm * Produces an abnormally wide QRS complex’s will be evident

Answer 2

* accessory/abnormal conduction pathway that short circuits the normal conduction pathway * Wolff-Parkinson-White Syndrome is an example of one of these pre-excitation syndromes It is characterised by an accessory pathway that passes from the atria to the ventricles without passing through the AV Node, consequently we lose the delay in the AV node that allows time for the atria to contract while the ventricles are relaxed The QRS complex will be abnormal (slightly wider because of the delta wave), instead of the Q caused by depolarisation of the septum, we get a delta wave

Answer 3

1. Abnormal automaticity * contractile myocytes that should otherwise lack automaticity spontaneously depolarise and produce action potentials ahead of schedule 2. Triggered activity * Where an extra action potential is triggered spontaneously during, or immediately following repolarisation 3. Re-entry * A loop in the conduction system results in self perpetuating depolarisations * By the time the wave of deplarisation reaches the end of the loop, the refractory period would have passed, and excitation would be possible

Answer 4

1. **Ischaemia** * Reduced oxygen levels as a result of ischemia, reduce the ATP levels in the cell, thus disabling the ion pumps and altering the ion gradients * Eventually this results increased sodium and increased calcium, resulting in a spontaneous depolarisation and inappropriate automaticity in the contractile myocytes 2. **Electrolyte imbalances** (particularly hypokalaemia) * can be caused by renal problems, excessive vomiting, diarrhoea 3. **Abnormally leaky channels** * The cell’s membrane may be abnormally leaky to Na+ or Ca2+ ions at rest (in Phase 4), producing a spontaneous depolarisation

Answer 5

1. Early after depolarisation (EADs) 2. Delayed after depolarisation (DADs)

Answer 6

* Second action potentials are triggered early on in the relative refractory period (phase 3) * These may occur in patients with abnormally long repolarisation times * Calcium and sodium channels may recover from inactivation (i.e. inactivation gates open) before the membrane potential is below their threshold of activation (hence both activation and inactivation gates are opened) → influx of Na+/Ca2+ → cell depolarises * EAD happens in long QT syndrome where there is abnormally long repolarisation time → Q wave and T waves become abnormally long → EADs is more likely to occur

Answer 7

* Are depolarisations that occur after the repolarisation phase is complete, but ahead of the sinus rhythm * This occurs during Phase 4 * DADs occur due to high intracellular Calcium and sarcoplasmic reticulum calcium level. When the sarcoplasmic reticulum is overloaded, it releases Ca2+. This trigger calcium to be released from the sarcoplasmic reticulum which evokes an action potential * DADs can be suggestive of * Heart failure * Digitalis (Digoxin) toxicity * Excessive catecholamines

Answer 8

1. Functional re-entry: * occurs when conduction velocity becomes abnormally slow 2. Anatomical re-entry: * occurs when part of the electrical conduction in the heart is through an unusually long pathway * E.g. due to hypertrophy

Answer 9

1. Premature atrial complexes 2. Atrial flutter 3. Atrial fibrillation 4. Premature ventricular complexes 5. Ventricular tachycardia 6. Ventricular fibrillation

Answer 10

1. atrial depolarisation is initiated by cells other than the SA node pacemaker cells within the atria 2. ECG 1. Abnormal P wave 2. The timing of these PACs is faster than the normal sinus atrial rhythm 3. compensatory pause on the ECG until sinus rhythm can re-establish itself 3. Can be caused by inappropriate automaticity, an early afterdepolarisation (triggered activity) or delayed afterdepolarization (triggered activity) in atrial contractile myocytes

Answer 11

1. characterised by an atrial depolarisation rate of 240 – 350 bpm 2. Most often caused by a re entry loop 3. This will look like a saw tooth pattern of P waves, however will have a slower rate of ventricular depolarisation

Answer 12

1. characterised by chaotic depolarisation of the atria, which is accompanied by a ventricular depolarisation that is irregular and variable 2. Caused by multiple re-entry loops 3. Refer to 1

Answer 13

* Atrial muscle contracts randomly and weakly * Thus blood is static and jiggled -\> Coagulation

Answer 14

1. Spontaneous depolarisation of the ventricles 2. usually caused by inappropriate automaticity (associated with ischemia and electrolyte imbalance) or triggered activity (DADs or EADs) 3. ECG 1. Does not usually feedback into the atria, but rather just encompasses both ventricles, thus sinus rhythm is unaffected 2. As repolarisation will obviously follow a different path, the T wave is inverted 3. As depolarisation follows an unusual sequence, the QRS complex is usually abnormally long 4. The PVC will be ahead of the sinus rhythm, before we get a compensatory pause before the next sinus beat

Answer 15

1. 3 or more consecutive QRS complexes at a rate exceeding 100 bpm 2. caused by the formation of a re-entry loop 3. ECG 1. QRS complexes combine with T waves to form large, wide, undulating waves, with individual parts of the wave form being un recognisable (if the waves look the same they are known as monomorphic) 2. As it is unusual for ventricular depolarisation to move retrograde into the atria (it can happen in some situations), sinus rhythm is usually unaffected (P waves will be independent of the QRS) * However these waves are often not seen

Answer 16

Polymorphic ventricular tachycardia especially associated with Long QT syndrome (early afterdepolarisations

Answer 17

1. Characterised by rapid, chaotic electrical rhythm which is completely uncoordinated * This means that the muscle is depolarising and contracting, and repolarisation and relaxing with no coordination Ventricular muscle thus quivers rather than contracting in a coordinated manner * CO significantly diminished 2. Multiple Re-entry loops 3. Look at 1