ABC | Volume 114, Nº5, May 2020

Arq Bras Cardiol. 2020; 114(5):943-987 Guidelines Brazilian Cardiovascular Rehabilitation Guideline – 2020 important in young individuals who experience elevated HR during training. In older patients with HF who are on high‑dose beta blockers, the peak HR observed during CPET or TMET is usually below the threshold that triggers ICD therapy. Patients with an artificial pacemaker may have different chronotropic responses observed on CPET or TMET, which will impact the prescription of aerobic exercise. In addition, the individual’s own pace, type of pacemaker, and presence of a rate sensor will influence the HR response to exertion and, consequently, the exercise prescription. 351 The four possible types of artificial pacemaker response to exertion are as follows: 1) Normal or depressed sinus-node chronotropic response. Pacemaker inhibited (not triggered). The chronotropic response to stress is mediated by sinus rhythm and may be normal or depressed (due to sinus node dysfunction and/or drug effect). Ventricular conduction occurs via the own pathway, and the pacemaker is not triggered on exertion. In some cases, it can be triggered at rest and during initial loads, with atrial and/or ventricular pacing. However, during exertion, the pacemaker is inhibited, with a predominance of sinus responses and ventricular conduction via the own pathway. In this type of response to exertion, the intensity of exercise prescription should be based on the usual concerns and is entirely unaffected by the presence of an artificial pacemaker. 2) Normal or depressed sinus-node chronotropic response. Pacemaker triggered (activity-initiated ventricular pacing). The chronotropic response to exertion is mediated by the sinus rhythm. Sinus activity is sensed by the pacemaker and triggers synchronized ventricular pacing according to preset paced atrioventricular intervals. In this case, if the maximum pacemaker response limit has been set appropriately for the patient’s sinus response, the exercise prescription may be HR-based, as the ventricle will be paired with sinus activity. However, if the maximum pacemaker response limit is set lower than the patient’s sinus response, dyssynchrony of ventricular pacing and sinus activity will occur at moderate to high exercise intensity. The pacemaker will then block some sinus stimuli by mimicking AV-node Wenckebach activity, a phenomenon known as “electronic Wenckebach”, 352 in order to keep the ventricular HR within the programmed limit; a plateau in the chronotropic response to exertion will ensue. In this scenario, the loss of synchrony between sinus rhythm and ventricular rate will interfere with the utility of HR to guide exercise intensity. The exercise prescription should instead be based on relative loads and/or subjective perceived exertion. When the electronic Wenckebach phenomenon occurs, extreme care is required to detect it during CPET or TMET. It is essential to obtain precise information on the atrial rate at which the pacemaker will initiate 2:1 block, because as this rate is reached, ventricular pacing will occur at a 2:1 ratio, with the potential for a sudden fall in HR on exertion and an abrupt, symptomatic reduction in cardiac output. Therefore, unless the programmed Wenckebach interval and the 2:1 block rate are quite far apart, the HR which triggers electronic Wenckebach may be used as the upper limit for CPET or TMET, as well as for the exercise prescription. In such cases, pacemaker reprogramming to better match the patient’s sinus response should be considered and discussed with the primary physician. Another option, depending on the clinical picture, is the optimization of drug therapy with negative chronotropic agents (such as beta blockers). A reduced sinus response may prevent the aforementioned event. 3) Fixed, pacemaker-mediated chronotropic response (no rate responsive pacing). Some patients may have no sinus activity at all, as in atrial fibrillation. In these cases, individuals with complete AV block will be completely dependent on ventricular pacing. If the pacemaker has no rate responsive pacing, or if the sensor is disabled, there will be no chronotropic response to exertion; the pacemaker will be set to a fixed HR. This type of pacemaker and programming is now exceedingly rare. Nevertheless, in such patients, the HR is useless to guide exercise prescription, which should instead be based on relative loads and/or subjective perceived exertion. 4) Pacemaker-mediated chronotropic response (rate responsive pacing). In patients with atrial fibrillation and AV block, as previously described, but whose artificial pacemaker has an active sensor with rate responsive pacing, there will be dependence on ventricular pacing, but activation of the sensor by exertion will lead to a pacemaker-mediated chronotropic response. In patients with sinus rhythm, but with a large chronotropic deficit due to sinus node dysfunction and/or drug effects, a chronotropic response to exertion may also occur, mediated by the pacemaker sensor, with atrial pacing followed or not by ventricular pacing. The speed and magnitude of the rate sensor’s response to exertion are programmable, with the possibility of adjusting the sensor activation threshold, the rate of increase in HR to exertion and the rate of reduction during recovery, and the maximal HR limit for the sensor. TCPE or TMET can be used to verify the adequacy of the response and identifying potential needs for pacemaker reprogramming, which should be discussed with the patient’s primary physician. In such cases, as the chronotropic response will be artificially mediated by the device, HR-based prescription of exercise intensity may be inaccurate. Therefore, the use of relative loads and/or perceived exertion is preferred. Pacemakers with accelerometer sensors and axial motion detection, which are the most common, have a sensitive response to walking or running on a treadmill. However, as there is no vertical movement on a cycle ergometer, the sensor is activated very little or not at all. As a result, there is inferior chronotropic response during ciclo ergometer exercise, which may vary according to the individual response of the patient. 972