* '''AAI''': The atria are paced, when the intrinsic atrial rhythm falls below the pacemaker's threshold.
* '''VVI''': The ventricles are paced, when the intrinsic ventricular rhythm falls below the pacemaker's threshold.
* '''VDD''': The pacemaker senses
the atrial and ventricular events, but can only pace the ventricle. This type of pacemaker is used in patients with a reliable sinus node, but with an AV-block.* '''DDD''': The pacemaker records both the atrial and ventricular rate and can pace either chamber when needed.
* '''DDDR''': As above, but the pacemaker has a sensor that records a demand for higher cardiac output and can adjust the heart rate accordingly.
* Biventricular pacemakers ('''CRT-P'''): Leads in both ventricles are present
to synchronized contraction. The lead pacing the left ventricle is usually positioned in the coronary sinus. This cardiac resynchronization therapy can improve symptoms and survival in some heart failure patients. Several optimizing methods are being evaluated to find the most effective pacing delay between left and right ventricles. They include echocardiography, finding the narrowest QRS, and invasive hemodynamic measurements with pressure and flow wires.
* '''[[ICD]]''' (Internal Cardioversion Device): This device can detect and treat [[Ventricular Tachycardia]] and [[Ventricular Fibrillation]]. ICDs are a separate category and usually not considered pacemakers although they do have a pacing function. Usually the first treatment is anti-tachy pacing (pacing at a rate +- 10% above the ventricular rate in ventricular tachycardia, which can convert the rhythm to sinus rhythm). If this is not effective, a defibrillator shock is delivered, usually with 16-36 Joules of energy. ICDs can save lives in patients who have a high risk of ventricular arrhythmias. All ICDs have optional pacemaker activity to treat bradycardias. New biventricular ICDs have 3 leads: an atrial lead, a left ventricular lead and a right ventricular lead.
* Biventricular ICDs ('''CRT-D'''): an ICD with biventricular pacing option.