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Fibrillation mechanisms - Coggle Diagram
Fibrillation mechanisms
VF
Fibrosis
Different types of fibrosis and gap junction remodeling result in different fibrillation patterns and different mechanisms for sustaining VF
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''structural and electrophysiological heterogeneity result- . ing from the interface between complex fibrosis and viable myocardium, . such as in PF and DiF, is a critical substrate for anchoring reentrant activity and sustaining globally organized fibrillation''
"Cells with spontaneous impulse generation may be silenced when tightly coupled to surrounding myocardial cells, having membrane potentials that are more negative. The strong electrical coupling may clamp the membrane potential of the pacemaker cell to such a negative value that pacemaker activity is suppressed."
"Clamping of the pacemaker cells can be reduced or prevented by uncoupling them from the surrounding nonpacemaker cells. This can be achieved by decreasing connexin expression and/or increasing collagen deposition, which also tends to separate the cells electrically."
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"Fibrosis may also play a role in arrhythmias based on abnormal impulse initiation such as automaticity and triggered activity."
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fibrosis --> tissue discontinuities --> slow conduction/conduction block --> spiral waves, vortex shredding
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Wu, 1998
"The most common mode of initiation of new reentrant wave fronts during VF was related to the conduction block caused by altered tissue anatomy"
"Ventricular tachycardia (VT) was defined as a run of four or more consecutive premature ventricular beats (including torsades de pointes) and ventricular fibrillation (VF) as when it was unable to distinguish individual QRS complex or to measure the beating rate."
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AF
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Ambrosi, 2011
"AF, on the other hand, involves multiple re-entrant circuits defined primarily by local excitability and refractory periods"
"Atrial flutter defined by a macro–re-entrant circuit, which can rotate around an anatomic or functional line of block. Major anatomical structures, including the region between the vena cavae and the pulmonary veins, are usually involved in defining re-entry"
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Clinical implications
Pacemaker-induced VF
"Most cases of ventricular fibrillation after cardiac pacing in acute myocardial infarction occur during manipulation of the temporary pacing electrode into the right ventricle, particularly after inferior or right ventricular myocardial infarction."
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Current leakage from pacemaker caused very high electrical stimuli to be delivered, resulting in VF
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Pacemaker induced VF caused by ICD, which then also terminated the VF
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"The presence of right ventricular infarctlon seems to be a contributing mechanism involved in the induction of ventricular fibrillation during temporary pacing for bradyarrhythmia complicating acute myo- cardial infarction."
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The probability of a pace- maker beat falling into a vulnerable period is further increased when two pacemakers are im- planted.
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precipitation of ventricular fibrillation by
a stimulus from a cardiac pacemaker, although with surgical atrioventricular block and im- an interesting theoretic possibility, has never planted cardiac pacemakers. Intravenous iso- been reported clinically.
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Himmrich, 2003
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If the pacemaker feature is switched on, an effective ventricular stimulus after the pause will lead to an ectopic ventricular excitation.
The more often a ventricle is paced, the higher is the chance of accidental coincidence of electrical instability and proar- rhythmic ventricular stimulation.
ERP
"Studies with rotigaptide that enhances gap junction conductance and con- duction velocity have shown that the increase in cell-to-cell coupling does not affect the refractory period"
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Animal models
Rat
VF
MI by LAD ligation
Chronic
Oikonomidis, 2010
Overall, the severity of VT/VF was greater in ETB-deficient rats, evidenced by higher (p = 0.0058) mortality (72.0% vs. 32.1%)
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Fernandes, 2005
1 ms pulse width, 2x threshold voltage
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"PES induced sustained VT in all groups of rats with myocardial infarction" 14-35 days after ligation
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Weigand, 2016
LAD ligation done, CHF developed with studies 6 weeks later
S1S2S3 stimulation for VT induction from RV
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VT
"Monomorphic ventricular tachycardia demonstrates a stable QRS morphology from beat to beat while polymorphic ventricular tachycardia has changing or multiform QRS variance from beat to beat.[1] Torsades de pointes is a polymorphic ventricular tachycardia that occurs in the setting of a long QT interval and appears as waxing and waxing QRS amplitude on ECG.[1]"
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"a form of VT in which there are multiple ventricular foci with the resultant QRS complex varying in amplitude, axis, and duration. The most common cause of PVT is myocardial ischaemia/infarction"
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"Torsades de pointes (TdP) is a specific form of PVT occurring in the context of QT prolongation — it has a characteristic morphology in which the QRS complexes “twist” around the isoelectric line."
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Nervous system
"Nerve remodeling as a result of MI is known to be an important genesis of life-threatening arrhythmias. It is hypothesized that neural modulation might serve as a therapeutic option of malignant arrhythmias"
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Following an ischemic insult, sympathetic axon fibers become dysfunctional and infracted, which is followed by neural remodeling char- acterized by nerve sprouting and heterogeneous patterns of sympathetic innervation
