What is Syncope?
A transient loss of consciousness due to transient global cerebral hypoperfusion characterised by sudden onset, short duration and a complete spontaneous recovery.
What is vasovagal syncope?
• A vasovagal episode is one that is mediated by the vagus nerve.
• The mechanism is as follows;
- Peripheral vasodilation and venous pooling of blood leads to a reduction in blood return to the heart.
- The near-empty heart then contracts vigorously which stimulates stretch receptors which trigger reflexes in the CNS.
- The CNS tries to reduce the stetch of the left ventricle through further vasodilation and bradycardia, leading to syncope.
What are some of the associated symptoms of vasovagal syncope?
Nausea, dizziness, sweating, tinnitus, yawning and a sinking feeling.
On an ECG trace how many ms is a small square worth?
How wide should a normal QRS complex be?
Up to 120ms, 3 small squares.
How wide should a normal PR interval be?
120-200 ms, 3-5 small squares.
What does the P wave represent?
It is atrial depolarisation.
What does a peaked, notched or enlarged P wave indicate? What may this be due to?
Atrial Hypertrophy, which may be due COPD, pulmonary emboli, vascular disease or heart failure.
Varying P waves may indicate what?
That the impulse is coming from various sites, possibly due to irritable atrial tissue or damage near the SAN.
What does the PR interval represent?
This is the atrial impulse through the AV node, bundles of His and left and right bundle branches.
A normal PR interval should last 120-200ms (3-5 small squares), what is indicated if it is longer or shorter than this range?
• Shorter- The impulse originated somewhere other than the SA node, this variation is associated in preexcitation syndromes and junctional arrhythmias.
• Longer - Delay through the atria or AV junction due to digoxin toxicity or heart block.
What does the QRS complex represent?
The depolarisation of the ventricles.
What might a deep, wide Q wave represent?
What might a notched R wave indicate?
A bundle-branch block.
What might a widened QRS complex indicate?
A ventricular conduction delay.
What does the ST segment represent?
This is the end of ventricular depolarisation and the start of ventricular repolarisation.
What might a depressed ST segment indicate?
Myocardial ischaemia or digoxin toxicity.
What might an elevated ST segment indicate?
What does the T wave represent?
It represents ventricular recovery or repolarization.
What might tall, peaked or tented T waves indicate?
They may indicate myocardial injury or hyperkalaemia.
What is second-degree type 1 block?
• Also known as Wenkebach.
• This is a progressively longer PR interval until a QRS complex is dropped and the cycle starts again.
What is second-degree type II heart block?
• This is where the PR interval is regular, but a QRS complex is dropped.
What is third-degree heart block?
This is when there is a complete dissociation between P-waves and QRS complexes.