Not all bigeminy is bigeminy

It may be Wenckebach with 3:2 block.

So, what you see is what appears to be an ectopic supraventricular beat because the P wave is on the T wave. You may also get a wider QRS because the coupling interval is short enough to cause aberrant conduction, and then you get a pause.

It is this pause which is the key.
The pearl is that you must look very hard here to make sure that there is not a P wave in it (easy if the P waves are big, but often they can be very flat).

The other thing to look for is the duration of the pause - if it's:
1. A VE - will block the AV node to the sinus beat but will not reset the sinus cycle - will give a pause that from the R wave of tbeat before the ectopic, to(2) the R wave of the beat after the ectopic, is exactly 2x the sinus cycle. This is called a "fully compensatory cause".
2. An SVE, because it resets the sinus cycle, will give a non-compensatory/LESS THAN COMPENSATORY pause
3. Heart block, will give a compensatory pause because it does not reset the sinus cycle.

So, with a VE, it's easy to tell because you see the VE.
Therefore the usefulness of this rule comes in when you are evaluating whether it is an SVE or a AV block.

Where the P's march through the QRS's

This is either AV dissociation (more Q's than P's) or CHB (more P's than Q's).

If there is a ventricular tachycardia in AV dissociation, then there may be one of the following present as well:
1. Atrial tachycardia
2. Normal atrial rate
2. Atrial bradycardia

Differentiating SVE from VE

There are two pearls to observe:
1. See if there are any non-aberrant ectopics and count the number of big squares between the R waves - this tells you the coupling interval length that will NOT impinge upon the refractory period of the bundle (usually the right bundle).
2. See if the T wave before the ectopic is different to all other T waves (it will usually be HIGHER).

V1-V3 lead misplacement

The way to pick that it is this, rather than a posterior MI, is to look at:

1. P wave - it will be biphasic in V3
2. RSR pattern - R wave in V1, S wave in V3, R wave in V4.

Hypercalcaemia

This teaches the importance of making sure that each ECG has an ST segment.

In hypercalcaemia, there is none, so the J point merges with the T wave and there is no flat bit (ST segment) in between.




This is because phase 2 (aka PLATEAU phase) of the action potential is shortened.



So, 0 is blast-off/depolarization (Sodium channels open)
1 is the notch (sodium channels close)
2 is plateau (calcium channels open, outward potassium channels open)
3 is repolarization (calcium channels close, potassium channels stay open)
4 is rest/electrically neutral

Good pacemaker gone bad

PACEMAKER SYNDROME:
The symptoms of pacemaker syndrome included dyspnea on exertion, paroxysmal nocturnal dyspnea, orthopnea, hypotension, pre-syncope, and even syncope. Heart failure signs include elevated neck veins, rales, and pedal edema. Physical exam can often reveal cannon A-waves. This sign occurs secondary to ventricular-atrial (V-A) conduction and the contraction of the atria against closed A-V valves. Although relatively uncommon, syncope has been attributed to pacemaker syndrome. Syncope is usually associated with systolic blood pressure declines of greater than 20 mm Hg that can occur with the onset of pacing. Additional symptoms attributed to pacemaker syndrome include easy fatigability, malaise, headache, and the sensation of fullness and pulsations in the head and neck. Pacemaker syndrome is most severe when intact V-A conduction is present⁶. The elevated venous pressures associated with the contraction against closed A-V valves causes a vagal afferent response resulting in peripheral vasodilation and hypotension.

So, it occurs if have retorgrade conduction of the paced ventricular signal, or if there is bidirectional block AND both the atrium and ventricle happen to also have the same rate of contraction!

PMT:
This is re-entry using the pacemaker lead.

So, what happens is that each paced beat always, in every pacemaker in the world, creates a retrograde atrial wave. This atrial wave is ignored by virtue of all pacemakers being programmed with a PVARP (postventricular atrial refractory period). But sometimes the VA conduction time is so slow that it outlasts the PVARP, and therefore reentry occurs.
How quick will the pacemaker go? Well, all pacemakers are programmed with an upper rate limit, so it will not exceed that.
The solution for this that companies have come up with and programmed some pacemakers with, is that the pacemaker, when it sees that it is consistently running at the upper rate limit, will intentionally drop a beat/intentionally fail to pace the ventricle for a beat. This ends the tachycardia :)

WHAT TO LOOK AT NEXT WHEN YOU THINK YOU'VE PICKED UP A LIMB LEAD MISPLACEMENT

The key differential is dextrocardia - you can tell it's not that because the R waves in dextrocardia are largest in V1 and smallest in V6.

Bythway, something that is often forgotten is that there is reversal of leads II and III because lead I is inverted.