What does the the box plot show?
This is a single-chamber ICD and therefore there is no information from the atrium. At the beginning of the trace the RR intervals are irregular and relatively long (none are less than 400 ms). This is due to underlying AF. There is then a sudden increase to a regular tachycardia with a cycle length of 300 ms (rate 200 bpm) which is entirely consistent with VT. There are 18 of these beats before the device appropriately detects VT, marked with the word detection appearing at time point 0. The giveaway that ATP is delivered is the word ‘Burst’ being documented, but it can also be seen that 8 beats occur at a slightly shorter RR interval than the VT before the successful termination of the VT and a return to AF with a slower irregular RR interval. These 8 beats are the ATP being delivered. It is important to scrutinize all the information on the programmer printouts carefully as each manufacturer gives the information in a different format.
With regard to ARVC:
To confirm the diagnosis two major, one major and two minor, or four minor criteria are needed, and therefore a diagnosis cannot be made solely on cardiac MRI. Asymptomatic patients with mild disease do not require an ICD. The condition is usually autosomal dominant, but currently genes are only identified in approximately 30% of cases.
A 57-year-old patient with a history of dilated cardiomyopathy and an ejection fraction of 20% is admitted to hospital after a presyncopal episode. His ECG on arrival shows monomorphic VT with a rate of 80 bpm and his BP is 70/50 mmHg. He receives urgent cardioversion and his QRS complexes are narrow on return to sinus rhythm. He is normally NYHA class III and is on maximum medication for HF.
NICE criteria regarding the need for the aetiology to be IHD only apply in the primary prevention setting, but this case describes the need for secondary prevention. The patient’s QRS is narrow; therefore a biventricular pacemaker is not indicated at present and it should be possible to programme the device so that pacing is not needed. The ICD will attempt to treat the monomorphic VT with ATP in this patient, and if this is successful there may well be no need to consider further suppression of VT with either medication or ablation.
An asymptomatic 32-year-old man has the ECG shown performed as part of a routine work medical examination.
The ECG shows pre-excitation. Even though the patient is asymptomatic there is a risk of SCD due to pre-excited AF. There is no consensus on the best way to risk stratify patients, but if non-invasive testing is preferred a 5-day monitor could be performed. However, its main use is to see whether the pathway is intermittent with a sudden loss of pre-excitation which would place the patient in a lower risk category. In answer C there is no loss of pre-excitation during the 5-day monitor and therefore it would not be reasonable simply to discharge him. EP studies allow risk stratification and then the possibility of ablating a high-risk pathway at the same time.
What is the rhythm shown in the strip
This ECG shows a regular broad complex tachycardia. It has several features of VT with an unusual morphology for RBBB, an axis of –90°, and positivity in aVR. The 12th beat is a fusion beat which clinches the diagnosis. The fact that this is ‘RBBB-like’ suggests that it arises from the left ventricle and then crosses over to the right ventricle in a way that is analogous to conduction in RBBB.
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