These changes allow for adjustment to the differences in the local environment at the site of infection, evasion of recognition by targeted antibodies, and contribute to the lack of an effective vaccine.In addition to the ability to rearrange the genes it already has, it is also naturally competent to acquire new DNA (via plasmids), via its type IV pilus, specifically proteins Pil Q and Pil T. These processes allow N. gonorrhoeae to acquire/spread new genes, disguise itself with different surface proteins, and prevent the development of immunological memory – an ability which has led to antibiotic resistance and has also impeded vaccine development. Phase variation
Phase variation is similar to antigenic variation, but instead of changes at the genetic level altering the composition of molecules, these genetic changes result in the turning on or off of a gene. Phase variation most often arises from a frameshift in the expressed gene. The Opacity, or Opa, proteins of N. gonorrhoeae rely strictly on phase variation. Every time the bacteria replicate, they may switch multiple Opa proteins on or off through slipped-strand mispairing. That is, the bacteria introduce frameshift mutations that bring genes in or out of frame. The result is that different Opa genes are translated every time. Pili are varied by antigenic variation, but also phase variation. Frameshifts occur in both the pilE and pilC genes, effectively turning off the expression of pili in situations when they are not needed, such as after colonization when N. gonorrhoeae survives within cells as opposed to on their surfaces.
In an electrophysiology study, trifascicular block due to AV nodal disease is represented by a prolonged AH interval (denoting prolonged time from impulse generation in the atria and conduction to the bundle of His) with a relatively preserved HV interval (denoting normal conduction from the bundle of His to the ventricles). Trifascicular block due to distal conduction system disease is represented by a normal AH interval and a prolonged HV interval. In the absence of symptoms, a prolonged AH interval is likely benign while a prolonged HV interval is almost always pathologic. Treatment
An implantable cardiac pacemaker or permanent pacemaker is recommended in the following clinical circumstances. Class 1 recommendation is the strongest recommendation. Level A evidence is the highest level of evidence.Class I

Bifascicular block + complete heart block, even in the absence of symptoms (1b)
Bifascicular block + 2nd degree AV Block Type 2, even in the absence of symptoms (1b)
Alternating bundle branch blocks, even in the absence of symptoms (1c)Class II

Bifascicular block + syncope + alternative causes ruled out (e.g. orthostasis, arrhythmia) (2a)Class III (i.e. pacemaker not recommended)

Bifascicular block without symptoms
Bifascicular block + 1st degree AV Block, without symptoms

References
External links

http://www.ecglibrary.com/trifas.html
http://circ.ahajournals.org/content/97/13/1325.long - new guidelines in which trifascicular block terminology continues to be used.