Patient
Male implanted with a triple-chamber defibrillator (Cobalt CRT-D) for ischaemic cardiomyopathy; hospitalisation for loss of consciousness with a shock from the device
Take home message
- For each trace recorded by the system, a graph, the EGM and a summary are available, each providing information that is essential for a proper understanding of the event.
- Starting the analysis with the graph gives an overview of the episode (duration, therapies delivered, etc.) and the programmed parameters (number of zones and frequencies); the appearance of the graph is sometimes sufficiently characteristic to strongly suggest a diagnosis (cloud of points for a lead dysfunction, rail-like appearance for over-detection of the T wave, etc.).
- The analysis of the tracing is the essential part of the analysis, the choice of the 2 EGM tracks being configurable; for a double or triple chamber defibrillator, it is usual to programme the recording of the atrial bipolar channel and the ventricular bipolar channel to better understand the operation of the device and to facilitate differentiation between ventricular arrhythmias and supraventricular arrhythmias; for a single-chamber defibrillator, recording the shock channel between the box and the right ventricular coeli in addition to the bipolar channel may make it easier to interpret the tracing, as the shock channel provides information similar to that of an ECG lead.
- The summary sheet details the main parameters programmed (number of zones, zone limits, counters, discrimination, detection polarities and sensitivity values), which are essential for understanding how the episode works; each time an electric shock is delivered, it is essential to check the impedance of the shock, which provides decisive information about how well the device is working.
On this first page, we find a range of information relevant to the diagnosis made by the device: the type of episode (in this case, an episode classified as VF), the therapies (a 40 J shock is described as effective), the date and time of the episode, its duration and the mean atrial and ventricular frequencies.
The VF zone is divided into 2 zones: the TVR zone from 320 to 250 and the VF zone itself from 250 ms; the limit of the VF zone appears at 320 ms, which reflects the fact that the VF counter applies from 320 ms (same probabilistic counter for the TVR zone and the VF zone); the horizontal lines observed on the graph correspond to the limits of the programmed detection zones.
The graph allows analysis of the atrial and ventricular intervals over the whole episode; on the new defibrillator platforms from this manufacturer, additional information is available with differentiation between detected or paced atrial or ventricular cycles; in this example, at the start of the episode the atria are detected (white squares) and the ventricles are paced (black circles), which is expected on a CRT defibrillator.
The graph shows a sudden acceleration of the ventricular complexes with atrioventricular dissociation (ventricular frequency > atrial frequency) suggesting the diagnosis of a very rapid ventricular arrhythmia detected in the VF zone.
A maximum electric shock was delivered after an episode lasting around 16 seconds (5 seconds for the initial diagnosis, then 11 seconds for capacitor charging and confirmation at the end of charging); the electric shock appeared to be effective.
This plot shows EGM1 on the first line corresponding to bipolar atrial detection (Distal A/Anode A), EGM3 on the second line corresponding to bipolar ventricular detection (DistalVD/AnodeVD) and a third line with markers and intervals.
The first TF. marker corresponds to a cycle detected in the TVR zone, the FS markers to cycles detected in the FV zone.
This is ventricular fibrillation: ventricular arrhythmia (ventricular frequency > atrial frequency), very rapid (> 300 beats/minute), polymorphous and irregular.
The FD marker indicates that the initial FV counter programmed at 30/40 has been completed; 30 cycles classified as TF or FS can be counted; cycles detected in the TVR zone and in the FV zone implement the same FV counter.
Capacitor charging begins following the FD marker; in fact, a maximum electric shock corresponds to the first therapy programmed for this type of arrhythmia; during capacitor charging, unlike during initial detection, all cycles are systematically labelled VS regardless of their speed (slow or fast cycles).
The CE marker corresponds to the end of capacitor charging; this marks the start of the arrhythmia persistence confirmation phase; during this confirmation phase, all cycles (slow or fast) are also labelled VS; after 2 fast ventricular cycles, the electric shock is delivered (CD) and synchronised to the detection of a ventricular complex.
When the shock has been delivered, a blanking period of 520 ms begins, with no possibility of detection to avoid overdetecting the polarisation induced by the electric shock; there is also a period of 1200 ms following the shock, when no ventricular stimulation is possible; the electric shock was effective, with the return of sinus rhythm.
This summary sheet details certain elements specific to the episode (identical to those found on the graph), the charging time and the impedance of the shock delivered (an essential parameter for evaluating the operation of the device and therefore to be systematically checked when a shock has been delivered) as well as the main programming parameters.