Sinus node dysfunction, junctional escape rhythm, exertional dyspnea

ECG: Bradycardia with heart rate of 45 beats/minute, sinus node dysfunction with total absence of sinus P wave, likely junctional escape rhythm (regular and moderately slow QRS), with right bundle branch block pattern; retrograde conduction (negative atrial activity in inferior leads with fixed RP’ interval);

Comments: This patient was symptomatic with presence of asthenia and exertional dyspnea. The exercise test revealed a marked chronotropic incompetence with dyspnea appearing at the first stages in conjunction with a near total absence of heart rate acceleration and the persistence of a junctional escape rhythm without reappearance of normal sinus activity. The presence of this chronotropic incompetence without curable cause led to the decision to implant a pacemaker (class I indication). There is indeed consensus regarding the fact that implantation of a pacemaker does not improve the survival of patients with sinus node dysfunction but does allow to reduce associated symptoms. There is therefore no theoretical indication in asymptomatic patients (class III).

Take-home message: Chronotropic incompetence corresponds to a particular form of sinus node dysfunction with appearance or increase of symptoms in relation to an insufficient acceleration of the heart rate. The implantation of a controlled pacemaker (possibility of accelerating the pacing rate in response to exercise constitutes the reference treatment.