FIGURE 69-1 Thoracic impedance monitoring for heart failure monitoring.
EXPERT OPINION
Several manufacturer-specific algorithms exist to monitor for impending heart failure. Figure 69-1 shows the OptiVol fluid status monitoring algorithm available in Medtronic devices. The daily thoracic impedance trend is monitored and plotted at the bottom. The presence of pulmonary edema will decrease the daily thoracic impedance. The OptiVol fluid index is the difference between the daily impedance and the patient’s reference impedance, which is an internal reference that is updated on a continuous basis. This index will increase as risk of incipient overt heart failure increases. Figure 69-1 shows an upward trend in the OptiVol index for a few weeks prior to presentation consistent with the clinical impression of worsening heart failure. Thoracic impedance drop can also be due to fluid in the pocket or lead revision and pleural effusion. Hence, clinical correlation is essential in interpreting heart failure monitoring tools. In the absence of other precipitants of heart failure, clinical worsening in our patient was suspected to be due to high percentage of RV apical pacing. RV pacing avoidance algorithm, managed ventricular pacing, was enabled. Subsequently, the rate of RV pacing declined to 10%, and his ejection fraction improved to preimplantation levels.
WHY SHOULD WE MINIMIZE RIGHT VENTRICULAR PACING?
The premise behind programming to minimize ventricular pacing is the finding that frequent right ventricular pacing may induce ventricular dyssynchrony and left ventricular dysfunction. The Dual Chamber and VVI Implantable Defibrillator (DAVID) trial randomized patients with LV dysfunction undergoing implantation of an implantable cardioverter defibrillator (ICD) to either DDD pacing at 70 bpm or backup VVI pacing at 40 bpm.1 The trial noted a significant increase in death or hospitalization for heart failure in patients with DDD-70 compared to VVI-40. This was attributed to a significant reduction in the percentage of ventricular pacing in patients programmed to VVI-40 (4% versus 78%). The risk for heart failure increases with the percentage of RV pacing, with significant risk associated with >40% pacing. Post-hoc analysis of the Multicenter Automatic Defibrillator II (MADIT II) trial showed increased incidence of ventricular tachycardia with greater percentage of RV pacing.2 Hence several algorithms and programming strategies have been developed to promote intrinsic ventricular rhythm and minimize RV pacing.
STRATEGIES TO MINIMIZE VENTRICULAR PACING
Several programming strategies can be employed to avoid unnecessary RV pacing. Atrial only pacemaker (AAI) can be considered in patients with sinus node dysfunction and normal AV node. This is generally not preferred in patients with a history or risk of dysfunction of AV conduction.
Programming a low ventricular “back-up” pacing rate (such as 40 bpm) is recommended in patients with single chamber ICD who do not require antibradycardia therapy. This is supported by the DAVID trial described previously. Moreover, trials such as INTRINSIC RV and MVP trial did not establish superiority of advanced ventricular avoidance algorithms such as AV search hysteresis and MVP respectively over VVI back-up pacing in this population.3,4
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
