The effect of overdrive pacing rate and duration on ventricular escape rhythms in patients with chronic complete atrioventricular block

Idioventricular tachycardia and unstable ventricular escape rhythm in a canine patient with third-degree atrioventricular block

A 10-year-old female Labrador retriever was presented for evaluation and management of syncope. On presentation, idioventricular tachycardia (IT) was electrocardiographically evident but neither ventricular capture nor fusion complexes were recorded. Spontaneous termination of the IT resulted in prolonged ventricular asystole and revealed the underlying rhythm of third-degree atrioventricular block. The serum concentration of troponin-I was elevated, suggesting myocarditis, but this was not diagnostically confirmed. It is likely that overdrive suppression of subsidiary idioventricular pacemakers, and perhaps also disease of subsidiary ventricular pacemaker fibers, importantly contributed to the duration of asystole.

Stability of intrinsic rhythm in pacemaker-dependent patients during pacemaker replacement: Can we predict the need for temporary pacing?

BACKGROUND

In pacemaker-dependent patients, the risk of asystole must be managed during device replacement. This study aimed to examine whether we could predict the indication for temporary pacing (TP) during the generator replacement.

METHODS

We studied 105 consecutive patients who underwent pacemaker replacement due to battery depletion at Juntendo Nerima Hospital between September 2005 and December 2016. We examined the relationship between the stability of the intrinsic rhythm (IR) during pacemaker replacement and several clinical factors including age, gender, sick sinus syndrome or atrioventricular (AV) block, duration of pacing, structural heart disease, use of anti-arrhythmic drugs, and the presence/absence of a stable IR (>40 bpm) at the outpatient clinic (OPC) just before pacemaker replacement.

RESULTS

Of the 105 patients, we excluded 1 patient who required TP because of bradycardia-dependent torsades de points. Therefore, we evaluated 104 patients for the indication for TP. TP was underwent in 19 patients (18%) because of an absence or instability of the IR during pacemaker replacement. The indication for TP was significantly correlated with AV block (84% vs 48%, P = .0044) and the absence of a stable IR at the last OPC visit (89% vs 24%, P < .0001). For predicting the indication for TP, the following values of no stable IR at the last OPC visit were obtained: 89% sensitivity, 77% specificity, 46% positive predictive value, and 97% negative predictive value.

CONCLUSIONS

The presence of a stable IR at the last OPC visit was a good predictor (97%) of no indication for TP during pacemaker replacement.

Utility of isoproterenol in unmasking latent escape rhythm in pacemaker dependent patients undergoing pacemaker replacement

Pacemaker generator replacement in dependent patients may be managed with a bridging temporary pacing lead or by replacing the generator very expediently. The 2 options involve a small risk, and temporary pacing introduces additional cost. This study was conducted to explore the utility of a graduated rate-decrease protocol with isoproterenol support in unmasking an intrinsic rhythm that would obviate the 2 strategies. The protocol was used in 100 consecutive pacemaker-dependent patients (mean age 74.4 +/- 13.7 years, 56% men) who underwent permanent pacemaker replacement. Device lower rates were decremented in 1-minute intervals to 60, 50, 40, and 30 beats/min. If no intrinsic rhythm of > or =30 beats/min was observed after 1 minute, isoproterenol was infused at 1 microg/min for 2 minutes, followed by 2 microg/min for 2 minutes. Of the 100 patients, 59 demonstrated intrinsic rhythm during pacing step-down alone. Of the remaining 41 patients, 28 (68.3%) demonstrated intrinsic rhythm during isoproterenol infusion. The escape rhythm was junctional in 29%, idioventricular in 23%, conducted atrial fibrillation in 16%, and sinus in 15%. Only 13 of 100 patients (13%) failed to demonstrate adequate intrinsic rhythm after the protocol. In conclusion, this suggests that a standardized protocol to elicit an underlying rhythm in patients previously assessed as pacemaker dependent effectively minimizes the need for temporary pacing during device replacement.

New Onset of Pacemaker Dependency After Permanent Pacemaker Implantation

Pacemaker dependency has dangerous consequences under conditions of electromagnetic interference, unrecognized lead dysfunction, and battery depletion, and has been associated with cardiovascular and overall mortality. The aim of this study was to examine the incidence of new onset of pacemaker dependency during long-term follow-up after pacing system implantation. The study included 518 patients (mean age 72.9 +/- 10.4 years) who presented with intrinsic rhythms at the time of implantation. Indications for pacing were sick sinus syndrome (SSS) in 275 (53%) patients, AV block in 209 (40%), and AF with bradycardia in 34 (7%) patients. The mean follow-up was 3.7 +/- 2.7 years (range 1-17). Pacemaker dependency was defined as the absence of an intrinsic rhythm during backup pacing at 30 beats/min for 30 seconds. New onset of pacemaker dependency was observed in 23 (4.4%) of the 518 patients at a mean of 3.1 +/- 2.7 years of follow-up. Pacing indications were SSS in 6 (2.2%) of 275 patients, AV block in 15 (7.2%) of 209, and AF with bradycardia in 2 (5.9%) of 34. Patients with AV block had a significantly higher incidence of pacemaker dependency than patients with SSS (odds ratio 3.51; 95% CI 1.3 to 9.3; P = 0.012). The average annual rate of new pacemaker dependency was 1.6% during an 8-year follow-up. The incidence of new onset of pacemaker dependency varied among pacing indications, and was significantly higher in patients with AV block than patients with SSS.

Initial and long-term evaluation of escape rhythm after radiofrequency ablation of the AV junction in 50 patients

Between 1986 and 1994, 50 patients (mean age 63 +/- 13 years), 25 of whom had organic heart disease and presenting with atrial arrhythmias refractory to 5.6 +/- 1.6 antiarrhythmic drugs, underwent radiofrequency ablation (5 +/- 3 pulses by procedure; duration of pulses 50.5 +/- 32 s) of the proximal AV junction to create complete and permanent AV block. The escape rhythm was studied immediately after the procedure and during long-term follow-up. Immediately after the procedure, an escape rhythm was observed in 80% of the patients (junctional in 92%). Over a mean follow-up of 36 +/- 16 months in 47 patients (2 patients died before assessment of escape rhythm and 1 was lost to follow-up), an escape rhythm was present in 39 patients (83%) and absent in the remaining 8 (17%). The only significant difference between the two groups was the initial presence of an escape rhythm (P = 0.008). However, three patients with an initial escape rhythm had none during long-term follow-up. The initial presence of an escape rhythm as a predictive factor of its presence during follow-up had a sensitivity of 87%, specificity of 63%, positive predictive value of 92%, and negative predictive value of 50%. Thus, the absence of an escape rhythm during long-term follow-up causing pacemaker dependency was noted in 1 of 6 patients. This represents a limitation to this palliative treatment, which should be reserved for patients suffering from supraventricular tachycardias refractory to other treatments.