How does a pacemaker work and what does it do when the heart beats too fast?

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1. 1

   Fundamentals of pacemakers ECG interpretation - part 2.

   Journal of electrocardiology (de et al.)Published Jul 14, 2026Checked Oct 17, 2026

   “Ventricular tachycardia is identified by QRS morphology diverging from the known paced pattern, absent pacing spikes, and AV dissociation. Upper rate Wenckebach behavior mimics Mobitz type I AV block; 2:1 upper rate response mimics second-degree AV block. Ventricular pacing minimization algorithms produce isolated nonconducted P waves and prolonged AV intervals that simulate pathological conduction disease. Mode switching causes abrupt rate drops misidentified as output failure. Ventricular safety pacing generates a conspicuously short, fixed AV interval. Three discrete pacing artifacts reflect AV-sequential cardiac resynchronization therapy (CRT), ventricular safety pacing in CRT, or His-bundle pacing with backup RV output. Rate and AV hysteresis produce pauses and wandering AV intervals mimicking oversensing or Wenckebach periodicity.ConclusionsRecognizing algorithm-driven ECG patterns requires knowledge of device timing intervals and refractory periods, which lets clinicians distinguish programmed behavior from true malfunction or cardiac arrhythmia.”

2. 2

   ANTITACHYCARDIA PACING: OPTIMAL PROGRAMMING AND PREDICTION OF EFFICACY FOR THE TREATMENT OF VENTRICULAR ARRHYTHMIAS. STATE OF THE ART AND PERSPECTIVE.

   Research paper (Avolio et al.)Published Jan 3, 2023Checked Oct 17, 2026

   “Introduction: Antitachycardia pacing (ATP) is one of the therapies provided by an implantable cardioverter defibrillator (ICD) for the treatment of ventricular arrhythmias (VA). Successful ATP leads to avoidance of shock, that is related to an increase in mortality and morbidity. Methods and Results : A total of 63 documents have been obtained by using the key term “Antitachycardia pacing” in PubMed, focusing on optimal ATP and ICD programing to reduce inappropriate or avoidable therapies, predictive factors of ATP efficacy and latest technologies and devices still in experimentation. Antitachycardia pacing confirms to be a good therapeutic tool to interrupt ventricular arrhythmias. An optimal ICD programming could lead to the reduction of inappropriate or avoidable ATP therapies. Furthermore, a better knowledge in predictive factors of ATP efficacy not only could better orient physicians on the device to implant, but also could allow for a better arrhythmic risk stratification.”

3. 3

   When the Pacemaker Goes Rogue: Pacemaker-Induced Tachycardia, Syncope, and Car Crash.

   Case reports in cardiology (Grogg et al.)Published May 26, 2026Checked Oct 17, 2026

   “However, atrial threshold testing promptly provoked a PMT. The induced PMT led to a tachycardia of 130 bpm, causing severe symptomatic hypotension with a mean blood pressure falling below 50 mmHg. This could be easily reproduced several times. Given the patient's severe left ventricular systolic dysfunction and the absence of any overt alternative explanation, the PMT likely triggered the syncope preceding the car accident. Management focused on reprogramming the DR ICD. The most critical adaptation was a mode switch from DDD to DDIR to prevent atrial tracking, effectively terminating PMT episodes. A prolongation of the postventricular atrial refractory period (PVARP) was not possible due to the very slow VA conduction. The follow-up revealed no other episodes of PMT and the patient no longer experiences episodes of presyncope or syncope. This report highlights the potential for PMTs to induce severe hemodynamic instability and syncope, underscoring the importance of meticulous device evaluation.”

4. 4

   Reactive atrial‐based antitachycardia pacing therapy reduces atrial tachyarrhythmias

   Pacing and Clinical Electrophysiology (Crossley et al.)Published Apr 12, 2019Checked Oct 17, 2026

   “Of 43,440 qualifying patients, 4,203 had rATP on. Matching resulted in 4,016 pairs, totaling 8,032 patients for analysis. The rATP group experienced significantly lower risks of AT/AF events lasting ≥1 day (HR 0.81), ≥7 days (HR 0.64), and ≥30 days (HR 0.56) compared to control (P < 0.0001 for all). In subgroup analysis, rATP was associated with reduced risks of AT/AF events across age, sex, device type, baseline AT/AF, and preventive atrial pacing. Among real-world patients from a large device database, rATP therapy was significantly associated with a reduced risk of AT/AF. This association was independent of whether the patient had a pacemaker, defibrillator, or resynchronization device.”

5. 5

   2021 ESC Guidelines on cardiac pacing and cardiac resynchronization therapy

   European Heart Journal (Glikson et al.)Published Aug 29, 2021Checked Oct 17, 2026

   “evant public health authorities, in particular in relation to good use of healthcare or therapeutic strategies.Health professionals are encouraged to take the ESC Guidelines fully into account when exercising their clinical judgement, as well as in the determination and the implementation of preventive, diagnostic, or therapeutic medical strategies; however, the ESC Guidelines do not override, in any way whatsoever, the individual responsibility of health professionals to make appropriate and accurate decisions in consideration of each patient's health condition and in consultation with that patient and, where appropriate and/or necessary, the patient's caregiver.Nor do the ESC Guidelines exempt health professionals from taking into full and careful consideration the relevant official updated recommendations or guidelines issued by the competent public health authorities, in order to manage each patient's case in light of the scientifically accepted data pursuant to their respective ethical and professional obligations.It is also the health professional's responsibility to verify the applicable rules and regulations relating to drugs and medical devices at the time of prescription.”