True vs. pseudo-electrical ventricular alternans sustained by ventricular premature complexes.

This report describes a form of electrical ventricular alternans sustained by ventricular premature complexes (VPC). Alternans was associated with a constant heart rate (RR interval) and was therefore considered to be either a form of classic or true alternans or a mimic of the configuration seen in true alternans from other causes. In contrast, VPC-induced pseudo-alternans is characterized by an inconstant heart rate (RR interval). It is surprising that the incidence of true VPC-induced alternans is unappreciated and virtually unreported, most probably since the measurement of the RR intervals involving late VPCs is ignored.

A review of the atrial upper rate algorithms of St. Jude Medical (Abbott) cardiac implantable electronic devices : Incidence of repetitive nonreentrant ventriculoatrial synchrony (RNRVAS).

This review focuses on the manifestations of the three triggered atrial upper rate functions of St Jude Medical cardiac implantable electronic devices. The occurrence of repetitive nonreentrant ventriculoatrial synchrony (RNRVAS) is also evaluated as a basis for the development of automatic mode switching (AMS) and as a trigger for atrial tachycardia/atrial fibrillation (AT/AF) event recordings. RNRVAS is a common trigger for AMS because all the atrial events or intervals are used to calculate the filtered atrial rate interval (FARI). Once AMS is initiated, it will also effectively stop RNRVAS because entry into AMS also shortens the postventricular atrial refractory period (PVARP). Recent design developments to eliminate or minimize unusual upper rare responses include the following: (1) P waves in the PVARP are no longer counted towards the FARI if they are followed by an atrial paced event. (2) In new devices the AT/AF detection algorithm substitutes the Moving Average Interval (a relatively complex calculation) with the new FARI average. (3) Improved design of the rate-responsive PVARP with a far more aggressive response than in the past (enhanced atrial protection interval).

Diagnosis of myocardial infarction and ischemia in the setting of bundle branch block and cardiac pacing.

The diagnosis of myocardial infarction (MI) in the presence of left bundle branch block (LBBB) or during ventricular pacing (VP) is challenging because of inherent changes in the sequence of ventricular depolarization and repolarization associated with both conditions. Although LBBB and right ventricular (RV) pacing may both produce abnormalities in the ECG, it is often possible to diagnose an acute MI (AMI) or an old MI based on selected morphologic changes. Primary ST-segment changes scoring 3 points or greater according to the Sgarbossa criteria are highly predictive of an AMI in patients with LBBB or RV pacing. The modified Sgarbossa criteria are useful for the diagnosis of AMI in patients with LBBB; however, these criteria have not yet been studied in the setting of RV pacing. Although changes of the QRS complex are not particularly sensitive for the diagnosis of an old MI in the setting of LBBB or RV pacing, the qR complex and Cabrera sign are highly specific for the presence of an old infarct. Diagnosing AMI in the setting of biventricular (BiV) pacing is challenging. To date there is minimal evidence suggesting that the traditional electrocardiographic criteria for diagnosis of AMI in bundle branch block may be applicable to patients with BiV pacing and positive QRS complexes on their ECG in lead V1. This report is a careful review of the electrocardiographic criteria facilitating the diagnosis of acute and remote MI in patients with LBBB and/or VP.

Unusual cause of desynchronization in a cardiac resynchronization device.

This report describes a new cause of desynchronization encountered in a cardiac resynchronization device functioning in the VVIR mode. Left ventricular stimulation was inhibited when the sensor-driven rate exceeded the programmed left ventricular (LV) maximum trigger rate. With these devices, it is important to program the LV maximum trigger interval (essentially equivalent to a LV upper interval) to a value equal or faster than the sensor-driven upper rate.

Direct His bundle and paraHisian cardiac pacing.

The success rate of direct His bundle pacing (DHBP) and paraHisian pacing has improved remarkably in the last 3-5 years with the advent of dedicated fixation systems that have reduced procedural duration, dislodgement rate, and fluoroscopy time. The methodology of DBHP remains still more complex than paraHisian pacing and is associated with high-pacing thresholds. Thus, DHBP entails greater battery current drain and reduced device longevity. A shift toward paraHisian pacing (which is fusion pacing of myocardium and His bundle) has occurred because its implementation is easier and the electrical parameters are superior to those of DBHP. Currently, an additional safety lead is inserted at the RV apex or outflow tract to prevent asystole, especially in patients with pure DHBP. It is often possible to avoid a safety lead with paraHisian pacing because ventricular pacing is virtually assured on a long-term basis via myocardial capture. DBHP and paraHisian pacing can be achieved in a substantial proportion of patients with varying grades of narrow QRS AV block or after AV junctional ablation and in some patients with the ECG manifestation of bundle branch block caused by an intraHisian lesion. Preliminary observations suggest that DHBP may be useful in some patients requiring cardiac resynchronization if it produces a narrow QRS complex because the site of an intraHisian lesion responsible for left bundle branch block is above the site of DHBP.

P-wave locking in the postventricular atrial refractory period of cardiac resynchronization devices. Management with the Biotronik system.

Electrical desynchronization in cardiac resynchronization therapy (CRT) occurs when sinus P waves are continually locked in the postventricular atrial refractory period (PVARP). This process is characterized by sequences of a P wave as an atrial event in the PVARP followed by a conducted and sensed ventricular event. Such sequences are more common in patients with a prolonged PR interval, often initiated by premature ventricular complexes (PVC) and terminated by PVCs or slowing of the sinus rate. Specific algorithms automatically identify a recurring pattern of P wave locking in the PVARP, whereupon they shorten the PVARP temporarily until atrial tracking is restored with the programmed sensed AV interval. The Biotronik family of Lumax CRT devices use an AV control window which is not an algorithm that "unlocks" P waves trapped in the PVARP. Rather, it prevents P waves from becoming trapped in the PVARP. A ventricular sensed event occurring within the AV control interval does not start a PVARP so that P wave locking cannot occur when the AV conduction time is shorter than the AV control interval.

Using devices with a variable postventricular atrial refractory period for cardiac resynchronization.

Automatic postventricular atrial refractory period (Auto-PVARP) is a dynamic interval designed to provide a longer PVARP at slower rates to enhance protection against pacemaker tachycardia (PMT) and a shorter PVARP to enhance atrial sensing at high rates. Auto-PVARP is often programmed in Medtronic devices for cardiac resynchronization therapy (CRT) with little knowledge of its intricate manifestations and disadvantages. The use of Auto-PVARP is contradictory to the universal teaching that CRT devices should be programmed with a short PVARP. We present the sequential ECGs of a patient with a CRT device programmed with Auto-PVARP in whom the atrial rate was increased with isoproterenol to simulate exercise. The recordings demonstrated that Auto-PVARP produced a substantial delay in the restoration of AV synchrony from the time the spontaneous atrial rate dropped below the programmed upper tracking rate. Auto-PVARP makes little sense (especially in the presence of first-degree AV block) in CRT patients considering that PMT is rare in this situation. In CRT patients, one should program a short and fixed PVARP of ≤ 250 ms.

Impact of increasing current drain in a pacemaker operating during activation of the elective replacement indicator.

The occurrence of a 13.8 s episode of ventricular asystole in a patient whose VVIR pacemaker displayed the elective replacement indicator (ERI) is reported. Increasing battery current drain by VARIO testing and programming of the emergency VVI mode markedly increased battery current drain with a resultant decrease in the battery voltage below the pacing threshold. The prolonged lack of capture occurred because the lowered battery voltage could not return instantaneously to its previous level after the demand for a higher battery current drain had ceased. Rather, the battery voltage increased progressively to its previous level and successful capture was eventually regained at the previous base rate. When a pacemaker is at or near the ERI point, it is important to avoid any manipulation (including VARIO testing) that increases battery current drain so as to prevent prolonged ventricular asystole in pacemaker-dependent patients.

Esophageal contour changes during cryoablation of atrial fibrillation.

BACKGROUND: We have observed contour changes of the barium-filled esophagus during atrial fibrillation (AF) ablation with cryo-energy delivered in direct proximity to the esophagus. OBJECTIVE: To evaluate the frequency, location, and severity of esophageal contour changes during cryo-energy application close to the esophagus. METHODS: We retrospectively analyzed cine-fluoroscopic images acquired during hybrid cryo-radiofrequency AF ablation in 100 consecutive patients with cryo-energy delivered only in direct proximity to the esophagus. RESULTS: Esophageal contour changes were observed in 28 (32%) of 89 patients (and 74 [6.2%] of 1,191 of all cryo applications). They were more frequent in the left common pulmonary vein (PV) (50%) and less so in the right common PV and the upper PVs (4-5%). The distance of the ablation catheter from the endoesophageal contour prior to cryo-energy applications associated with contour changes was 1.8 +/- 1.5 mm, which increased to 4.1 +/- 1.6 mm at the time of peak contour change (P < 0.001). The esophageal contour deformation was 2.3 +/- 0.9 mm. There were no apparent complications related to cryo-energy application for 3-4 minutes, even if associated with contour changes. CONCLUSION: Esophageal contour changes were observed in >6% of cryo applications in direct proximity to the esophagus (32% of patients) and were most frequent in the posterior aspect of the left common and right lower PV ostium when cryo-energy was delivered at a distance of

Significance of syncope in patients with Alzheimer's disease treated with cholinesterase inhibitors.

We describe three cases of patients with Alzheimer's disease who presented with cardiac syncope soon after initiation of a cholinesterase inhibitor therapy (donepezil). Bradyarrhythmia was documented in two patients, considered probable in one, and was presumed related to the cholinergic therapy. Pacemaker implantation seemed justified rather than donepezil cessation. More over, it permitted an increase in donepezil dosage.

Triboelectric simulation of pacemaker malfunction.

We report the occurrence of a triboelectric phenomenon (static electricity) that mimicked malfunction of a contemporary pacemaker by creating an electrocardiograpic artifact virtually identical to the pacemaker stimuli. The diagnosis was established by observing a subtle overshoot of the questionable deflection that was absent from pacemaker stimuli.

High impedance leads and safety margin. Electrical considerations based on a simplified expression of the 'paradigm'.

For physicians who are not familiar with the electrical basis of cardiac stimulation, high impedance leads previously (10 years ago) considered as bad electrodes (high voltage) are now considered as the 'epitome' of lead technology (low energy drain): clearly impedance is not a good parameter for characterizing the qualities of a pacing lead. Using a simplified approach to the electrostimulation 'paradigm', it is easy to establish that modern high impedance leads are in fact high current density leads and high efficiency leads (better description). It is also possible to establish that routine programming of the safety margin at 100% above threshold parameters is associated with a decrease in the penetration of the electric field according to the reduction of the cathode surface area. For safety and energy saving, a small tip electrode could be combined with a low polarization surface treatment and a reduction in fibrosis development between electrode and myocardium.

A reappraisal of pacemaker timing cycles pertaining to automatic mode switching.

Automatic mode switching algorithms of dual chamber pacemakers require fundamental changes in the operation of pacemaker timing cycles to optimize detection of supraventricular tachyarrhythmias. The timing cycles related to mode switching are basically independent of the algorithm design. Blanking periods (when the sensing amplifier is temporarily disabled) should be optimized to a relatively small fraction of the pacing cycle to enhance atrial sensing and prevent far-field sensing. This review explains the function of the timing cycles pertaining to mode switching and proposes simpler terminology to facilitate the understanding of pacemaker function and electrographic interpretation of complex recordings.

Case report: complex arrhythmia induced by noncompetitive atrial pacing algorithm of DDDR pacemaker.

This report describes the occurrence of a repetitive nonreentrant ventriculoatrial (VA) synchronous rhythm precipitated by the noncompetitive atrial pacing algorithm of a Medtronic DDDR pacemaker. This algorithm delivers an atrial stimulus 300 ms after the detection of an atrial signal in the postventricular atrial refractory period of the pacemaker. In our patient, the atrial stimulus released by the algorithm was ineffectual because it encountered prolonged refractoriness of the atrial myocardium. This situation produced a repetitive nonreentrant VAl synchronous rhythm in the setting of retrograde VA conduction.