Atrial pacing, the forgotten pacing mode

In patients with sick sinus syndrome and normal atrioventricular conduction, physiological pacing can be accomplished with either a single chamber atrial pacemaker AAI/R or a dual chamber pacemaker DDD/R. The single chamber device has the advantages of simpler implantation and lower initial costs, while the dual chamber device offers protection in case atrioventricular conduction disturbances develop in the future. When rigorous attention is paid to the pre-implantation selection criteria, the incidence of reported second- or third-degree atrioventricular block varied between 0.4 and 1.8% per annum. Medical practice, however, has shifted to predominant implantation of DDD/R pacemakers in more than 95% of patients with sick sinus syndrome. Recent publications have reported an increase in left atrial diameter, decrease in left ventricular fractional shortening and increased incidence of atrial fibrillation in patients with DDD/R pacing as compared with patients with single chamber atrial devices. These changes were proportional to the percentage of ventricular paced beats. New algorithms in dual chamber devices have been developed in order to minimise ventricular stimulation. These are being evaluated at present. In my opinion there is still a place for atrial pacing in selected patients with sick sinus syndrome with a minimum risk of developing complete atrioventricular block. (Neth Heart J 2008;16(suppl 1): S25-S27.)     

Permanent parahisian pacing

Right Ventricular Apical permanent pacing could have negative hemodynamic effects. A physiologic pacing modality should preserve a correct atrio-ventricular and interventricular synchronization. This can be obtained through biventricular pacing, left ventricular pacing, or from alternative right ventricular pacing sites. Direct His Bundle Pacing (DHBP) was documented as reliable and effective for preventing the desynchronization and negative effects of right ventricular apical pacing. It is, however, a complex method that requires longer average implant times, cannot be carried out on all patients and presents high pacing thresholds. On the contrary, the parahisian pacing, with simpler feasibility and reliability criteria, seems to guarantee an early invasion of the His-Purkinje conduction system, with a physiological ventricular activation, very similar to the one that can be obtained with direct His bundle pacing. We present our experience on 68 patients who underwent a permanent right ventricular pacing in hisian/parahisian region, for advanced AV block and narrow QRS. In the first 17 patients we performed a double-blind randomized controlled study, with two 6-months cross-over periods in parahisian and apical pacing, documenting a significant improvement of NYHA class, exercise tolerance, quality of life score, mitral and tricuspidal regurgitation degree, and interventricular mechanical delay. In the subsequent 51 patients, in a mean follow of 21 months/patient, the pacing threshold remained stable (0.7+/-0.5 V implant; 0.9+/-0.7 V follow-up; p=0.08). The ejection fraction maintained medium-long term stable values, confirming the fact that the parahisian pacing can prevent deterioration of the left ventricular function. Parahisian pacing, therefore, has proven to be a reliable method, easy to apply and effective in preventing the negative effects induced by non-physiological right ventricular apical pacing.     

Intrinsic anti-tachycardia pacing terminated ventricular tachycardia resistant to traditional anti-tachycardia pacing

Implantable cardioverter-defibrillators (ICDs) serve to reduce the risk of sudden death; however, ICD shocks worsen patient prognosis. Therefore, attempts have been made to terminate life-threatening arrhythmias without ICD shocks. A 71-year-old man with non-ischemic cardiomyopathy, who previously underwent cardiac resynchronization therapy-defibrillator (CRT-D) placement, was hospitalized for ventricular tachyarrhythmia (VT) that was refractory to traditional anti-tachycardia pacing (ATP). Endocardial and epicardial ablation failed to prevent VT recurrence. Since the CRT-D battery was exhausted, it was replaced with a Cobalt? XT HF CRT-D (Medtronic, Minneapolis, MN, USA), and the intrinsic ATP (iATP) algorithm was employed. Although VT recurred frequently, recurrent VTs were terminated by the iATP, which created a conduction block in the circuit without VT acceleration or shock. This is the first reported case wherein an iATP algorithm was effective against VT resistant to traditional anti-tachycardia pacing. This novel ATP algorithm has the potential to terminate refractory VT without ICD shocks and provide a better prognosis.     

Reverse RAMP (REVRAMP) pacing: A novel anti tachycardia pacing technique

Anti-tachycardia pacing (ATP) is frequently used to terminate ventricular tachycardia (VT), however it is not always successful and may accelerate VT requiring defibrillation. REVRAMP is a novel concept of ATP that involves delivering pacing at a faster rate than VT, but instead of abruptly terminating pacing after eight beats, pacing is gradually slowed until VT continues or normal rhythm is restored. In a pilot study we show that REVRAMP can restore normal rhythm, and that if REVRAMP is unsuccessful, VT is not accelerated.     

Clinical advances in diaphragm pacing

Diaphragmatic pacing is a valuable tool that can significantly benefit certain patients with respiratory insufficiency provided they have an intact phrenic nerve and a functional diaphragm. Careful patient selection is critical to successful long-term results. The main populations that derive benefit from pacing include those with congenital or acquired central hypoventilation syndrome and more commonly those with a high cervical spinal cord injury, where the phrenic nerves remain intact. The pacing electrode of most phrenic nerve pacemakers is implanted directly on the phrenic nerve. A newer device relies on intramuscular implantation of the electrode on the diaphragm at the phrenic nerve motor point. Most patients can be successfully weaned from mechanical ventilation for a substantial time each day, if not completely. This has significant impact on quality of life and implications for healthcare costs. The potential exists for application of this technology to patients with other types of respiratory failure as investigative experience emerges. These include the chronic progressive disease, amyotrophic lateral sclerosis, or temporary scenarios in difficult-to-wean intensive care unit patients. This enabling technology should hold a place in the thoracic surgeon's armamentarium.     

Sensors for rate responsive pacing

Advances in pacemaker technology in the 1980s have generated a wide variety of complex multiprogrammable pacemakers and pacing modes. The aim of the present review is to address the different rate responsive pacing modalities presently available in respect to physiological situations and pathological conditions. Rate adaptive pacing has been shown to improve exercise capacity in patients with chronotropic incompetence. A number of activity and metabolic sensors have been proposed and used for rate control. However, all sensors used to optimize pacing rate metabolic demands show typical limitations. To overcome these weaknesses the use of two sensors has been proposed. Indeed an unspecific but fast reacting sensor is combined with a more specific but slower metabolic one. Clinical studies have demonstrated that this methodology is suitable to reproduce normal sinus behavior during different types and loads of exercise. Sensor combinations require adequate sensor blending and cross checking possibly controlled by automatic algorithms for sensors optimization and simplicity of programming. Assessment and possibly deactivation of some automatic functions should be also possible to maximize benefits from the dual sensor system in particular conditions. This is of special relevance in patient whose myocardial contractility is limited such as in subjects with implantable defibrillators and biventricular pacemakers. The concept of closed loop pacing, implementing a negative feedback relating pacing rate and the control signal, will provide new opportunities to optimize dual-sensors system and deserves further investigation. The integration of rate adaptive pacing into defibrillators is the natural consequence of technical evolution.     

Atrial fibrillation and pacing algorithms

Pacing prevention algorithms have been introduced in order to maximize the benefits of atrial pacing in atrial fibrillation prevention. It has been demonstrated that algorithms actually keep overdrive atrial pacing, reduce atrial premature contractions, and prevent short-long atrial cycle phenomenon, with good patient tolerance. However, clinical studies showed inconsistent benefits on clinical endpoints such as atrial fibrillation burden. Factors which may be responsible for neutral results include an already high atrial pacing percentage in conventional DDDR, non-optimal atrial pacing site and deleterious effects of high percentages of apical ventricular pacing. Atrial antitachycardia pacing (ATP) therapies are effective in treating spontaneous atrial tachyarrhythmias, mainly when delivered early after arrhythmia onset and/or on slower tachycardias. Effective ATP therapies may reduce atrial fibrillation burden, but conflicting evidence does exist as regards this issue, probably because current clinical studies may be underpowered to detect such an efficacy. Wide application of atrial ATP may reduce the need for hospitalizations and electrical cardioversions and favorably impact on quality of life. Consistent monitoring of atrial and ventricular rhythm as well as that of ATP effectiveness may be extremely useful for optimizing device programming and pharmacological therapy.     

Permanent direct His bundle pacing: initial report showing technical feasibility of an alternative pacing therapy

To prevent deterioration of left ventricular function during right ventricular apical pacing, permanent direct His bundle stimulation can be considered in selected patients with low left ventricular ejection fraction and a normal His-ventricle conduction time. We describe our first short-term experiences with permanent direct His bundle pacing in three patients. In two patients His bundle stimulation was still effective at six weeks'' follow-up. In one patient loss of capture was registered, after which conventional RV apical pacing was performed.     

Permanent cardiac pacing for neurocardiogenic syncope

Vasovagal syncope is not a benign condition in the elderly population. In patients not responsive to conservative therapy and whose abrupt faints are associated with serious injuries and seriously affected quality of life, pacemaker therapy was suggested. However, the usefulness of cardiac pacing for the prevention of recurrences of vasovagal syncope remains controversial because of the dominant role of the vasodepressor component during the episode. In the Medical Center Alkmaar, the Head-Up Tilt Test (HUTT) has been used since 1996 during the work-up of patients who present with vasovagal syncope. The HUTT showed a dominant cardioinhibitory response in 4.5% of our patients; in elderly patients with vasovagal syncope without prodromal symptoms and refractory on conservative therapy, pacemaker therapy was very effective in preventing syncope during long-term follow-up. (Neth Heart J 2008;16(suppl 1):S15-S19.)     

Diaphragm pacing in ventilatory failure.

Diaphragm pacing, which entails electrical stimulation to the phrenic nerve, is an effective means of managing patients with ventilatory insufficiency and intact lowermotor-neurone innervation of the diaphragm. The pacing apparatus is used to pace the right and left hemidiaphragms alternately to avoid fatigue, which may damage the muscle irreversibly. Among the important benefits of pacing in quadriplegics with paralysis or respiratory muscles are the social and psychological advantages of not being dependent on a mechanical ventilator.