12 lead ECG

• atrial fibrillation
• spontaneous ventricular activation
• asynchronous ventricular pacing (ventricular undersensing); spontaneous QRS complexes do not inhibit ventricular pacing
• ventricular pacing in the vulnerable period (R/T)

Comments

• the sensitivity, expressed in millivolt (mV), depicts the ability of the pacemaker to properly sense spontaneous cardiac events
• a pacemaker is equipped with input filters that specifically detect P waves in the atrium and R waves in the ventricle based on the analysis of three characteristics of these electrical signals: rate spectrum, slope and amplitude
• adequate programming of the sensitivity level should allow sensing all spontaneous cardiac events occurring in the implanted chamber while not sensing events of a different nature (sensing of cardiac signals from the other chamber, myopotentials, interference, etc.)
• atrial or ventricular undersensing is reflected on the electrocardiogram by the presence of fixed pacing rate artifacts despite the presence of spontaneous complexes that do not inhibit pacing
• this tracing reveals ventricular undersensing, sometimes leading to pacing during a vulnerable period
• in the absence of proper sensing, the pacemaker operates in asynchronous mode with no possibility of inhibition due to the spontaneous ventricles
• there is a small theoretical risk of inducing a malignant polymorphic ventricular arrhythmia compromising patient survival