Electrocardiographic features of complete heart block
Constant RR interval
Constant PP interval
Varying PR interval
PP interval shorter than RR interval
The first three together are features of AV dissociation
What is the electrophysiological hall mark of intra Hisean block?
Split His potential is the hallmark of intra Hisean block. The escape focus is slower in case of intra Hisean block than supra Hisean block.
Ashman phenomenon in atrial fibrillation
When there is short RR interval following a long RR interval, the QRS terminating the short RR interval is wide due to aberrant conduction with right bundle branch block pattern. This is because refractory period lengthens when RR interval increases. Aberrancy is more likely to occur in the right bundle than the left bundle. The aberrant beat can be mistaken for a ventricular ectopic beat. Aberrancy may be sustained in subsequent beats due to concealed trans septal conduction.
What are the causes of irregularities in ventricular tachycardia?
Initial few beats in a ventricular tachycardia can be irregular. Polymorphic ventricular tachycardia can irregular. The most important causes of irregularity in ventricular tachycardia are capture beats and fusion beats.
Concertina effect
Varying QRS width in WPW syndrome due to varying degrees of pre-excitation is known as concertina effect. The more the pre-excitation, the shorter the PR interval and wider the QRS duration.
How can you differentiate a late diastolic ventricular ectopic from intermittent pre-excitation?
The PJ interval will be constant in WPW syndrome while it can vary in late diastolic ventricular ectopic beats.
What are the electrocardiographic features of parasystole?
Varying coupling interval
Inter ectopic interval has a common denominator other than 1
Fusion beats
This means that there is a constantly firing focus which is protected from the dominant rhythm.
What are situations in which you can have two independent rhythms on an electrocardiographic recording?
Piggy back (heterotopic) cardiac transplantation
Maternal and fetal electrocardiograms
Re-recording on a Holter cassette with incomplete erasure