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Neurologic Diagnosis
Published in Philip B. Gorelick, Fernando D. Testai, Graeme J. Hankey, Joanna M. Wardlaw, Hankey's Clinical Neurology, 2020
Antidromic conduction can be assessed in accessible sensory or mixed sensorimotor nerves by electrically stimulating the sensory nerve proximally (e.g. the median or ulnar nerve at the wrist) and recording the resulting sensory nerve action potential (SNAP) distally (e.g. from surface ring electrodes placed around the index or little fingers, respectively) (see Figure 1.44b). Alternatively, orthodromic conduction can be assessed by stimulating the distal sensory fibers (e.g. median nerve with electrodes on the palm or ring electrodes on the index finger) and recording the SNAP with electrodes over the nerve more proximally (e.g. median nerve at the wrist; Figure 1.46).
Supraventricular rhythms
Published in Andrew R Houghton, Making Sense of the ECG, 2019
Much less commonly, the re-entry circuit travels down the accessory pathway and back up through the AV node – this is an antidromic AVRT, and in this situation the QRS complexes are regular and broad. This occurs because the ventricles are depolarized via the accessory pathway, which means the impulses can't gain access to the His–Purkinje system and the depolarization has to occur from myocyte to myocyte (as with the delta wave). The heart rate is typically faster, and symptoms more marked, in antidromic than in orthodromic AVRT. Antidromic AVRT can be very difficult to distinguish from ventricular tachycardia (VT), and indeed can act as a trigger for VT or for ventricular fibrillation (VF).
Recognition of common arrhythmias
Published in John Edward Boland, David W. M. Muller, Interventional Cardiology and Cardiac Catheterisation, 2019
Nicholas P. Kerr, Rajesh N. Subbiah
An accessory pathway may also be present as a bystander during another SVT, producing a WCT with pre-excitation pattern. This situation (along with antidromic AVRT) is called pre-excited tachycardia. A clinically important scenario is pre-excited AF, which produces an irregularly irregular WCT that may be mistaken for VT. Some accessory pathways can enable very fast antegrade conduction if they have a short refractory period and produce AF with an extremely rapid ventricular response, which may rarely degenerate into ventricular fibrillation (VF). Hence, a small proportion of patients with Wolff–Parkinson–White are at risk of sudden cardiac death.
Cardiac arrhythmias in pregnant women: need for mother and offspring protection
Published in Current Medical Research and Opinion, 2020
Theodora A. Manolis, Antonis A. Manolis, Evdoxia J. Apostolopoulos, Despoina Papatheou, Helen Melita, Antonis S. Manolis
Supraventricular arrhythmias include APCs, regular SVT and atrial flutter (AFlu)/fibrillation (AF). The differential diagnosis for SVT in pregnant patients is similar to that for non-pregnant patients, and includes atrioventricular nodal reentrant tachycardia (AVNRT), orthodromic or antidromic atrioventricular reentrant tachycardia (AVRT) with the participation of an accessory pathway, and atrial tachycardias (ATs)14. A form of atrial tachycardia, albeit with fast atrial rates (250–350 bpm), is atrial flutter (AFlu)16. Fast AF, where some degree of regularization may be noted, may also be considered in the differential diagnosis of SVT. Increase in circulating plasma volume and hyperdynamic circulation in pregnancy can predispose to SVT. SVT can occur in pregnant patients both in those with or without SHD. Atrial tachycardias and AFlu/AF may occur more commonly in patients with underlying SHD.
Burst and high frequency stimulation: underlying mechanism of action
Published in Expert Review of Medical Devices, 2018
Shaheen Ahmed, Thomas Yearwood, Dirk De Ridder, Sven Vanneste
SCS is being used to treat neuropathic pain, failed back surgery syndrome (FBSS), complex regional pain syndrome (CRPS), angina pectoris, and ischemic limb pain [10–12]. SCS is advantageous in part because it is minimally invasive, making it a safer and more cost-effective technique than surgical methods. Furthermore, SCS can achieve targeted pain relief and even reduce opioid use, all with little to no side effects [13]. Traditionally, SCS therapy is delivered via tonic stimulation, usually with a frequency between 40 and 50 Hz, an amplitude between 2 and 4 mA, and a pulse width that falls between 300 and 500 µs. The mechanism of action of SCS can be understood through both spinal and supraspinal mechanisms [14,15]. Electrical stimulation produces both orthodromic and antidromic action potentials. The action potential travels antidromically into the dorsal horn, where Aβ fibers synapse with the wide-dynamic-range neurons and release inhibitory neurotransmitters such as γ-amino butyric acid (GABA) and adenosine. The orthodromic potentials travel to the dorsal column, inducing inhibition via serotonergic and noradrenergic pathways [16,17].
An interesting case of wide QRS tachycardia with left bundle branch block morphology
Published in Acta Cardiologica, 2019
Krishna Kumar Mohanan Nair, Narayanan Namboodiri, Hiren Kevadiya, Ajitkumar Valaparambil
A 30 year old gentleman is evaluated for recurrent palpitations. He has no underlying structural heart disease. During one of the episodes a regular wide complex tachycardia with left bundle branch block (LBBB) morphology, left inferior axis and late precordial transition is recorded (Figure 1, Panel A). No preexcitation is documented on basal surface electrocardiogram. The differential diagnosis entertained at this point are supraventricular tachycardia (SVT) with LBBB aberrancy, ventricular tachycardia and preexcited tachycardia – antidromic AV re-entrant tachycardia. He has undergone an electrophysiological study which showed progressive preexcitation on incremental pacing from right atrial free wall making ventricular tachycardia less likely. Atrial pacing induced clinical tachycardia which has identical QRS pattern as that during maximal preexcitation. During the LBBB tachycardia there is 1:1 AV relation, negative HV interval and right bundle (RB) electrogram (EGM) preceded the His bundle (HB) EGM (Figure 1, Panel B). Negative HV interval during tachycardia excludes SVT with LBBB aberrancy as the mechanism. Mapping catheter positioned at 8’O clock of the lateral tricuspid annulus showed a sharp high frequency signal, accessory pathway potential (AP), between the atrial and the ventricular electrograms. In view of the progressive preexcitation on incremental atrial pacing, negative HV interval during the LBBB tachycardia, preceding RB EGM to HB EGM during the tachycardia and demonstration of accessory pathway potential at 8’O clock of the lateral tricuspid annulus diagnosis of antidromic AV re-entrant tachycardia involving atriofascicular bypass tract is made and successfully ablated.