Diagnosis and Mapping
In the setting of either previous ablation lines or atrial scar, the
utility of the 12-lead ECG in the diagnosis of peri-mitral flutter is
limited. If the patient arrives in the laboratory in sinus rhythm, we
attempt to induce atrial flutter with burst atrial pacing and programmed
extrastimuli from the CS catheter. Induction of flutter can be
challenging and is often preceded by short periods of AF. The CS
activation pattern is usually the first clue to localise the AT.
Proximal to distal CS activation is expected with counter-clockwise
peri-mitral flutter but also seen with cavotricuspid isthmus-dependent
flutter, right ATs and tachycardias that originate from the right PVs or
interatrial septum. Distal to proximal activation occurs with clockwise
peri-mitral re-entry or tachycardias originating locally from the
lateral LA. Entrainment is the most important diagnostic manoeuvre and
is more rapid and accurate than any form of 3-dimensional (3D) mapping.
A post-pacing interval minus tachycardia cycle length of less than 20
milliseconds from the proximal, mid and distal CS electrodes is
consistent with peri-mitral flutter and may be confirmed with left
atrial mapping (see Figure 3). If not initially performed under general
anaesthetic, this is initiated prior to transseptal access. We would
then proceed with double transseptal, transesophageal echocardiogram
(TEE) guided access using SL1 sheaths, one of which is subsequently
exchanged for a steerable Agilis sheath. Thereafter, intravenous heparin
is administered to target an activated clotting time of ≥350 seconds. A
high-density multipolar mapping catheter is used to map the LA.
Entrainment from the LA roof as well as points on the anterior and
posterior walls is needed to exclude the possibility of dual or
multi-loop tachycardias. High density 3D electroanatomic mapping is then
performed to confirm activation patterns but predominantly to construct
a voltage map to guide the ablation strategy.