Man-Oi Tang

Intrathoracic Impedance Monitoring in Patients With Heart Failure. Correlation With Fluid Status and Feasibility of Early Warning Preceding Hospitalization

Background—Patients with heart failure are frequently hospitalized for fluid overload. A reliable method for chronic monitoring of fluid status is therefore desirable. We evaluated an implantable system capable of measuring intrathoracic impedance to identify potential fluid overload before heart failure hospitalization and to determine the correlation between intrathoracic impedance and standard measures of fluid status during hospitalization. Methods and Results—Thirty-three patients with NYHA class III and IV heart failure were implanted with a special pacemaker in the left pectoral region and a defibrillation lead in the right ventricle. Intrathoracic impedance was regularly measured and recorded between the lead and the pacemaker case. During hospitalizations, pulmonary capillary wedge pressure and fluid status were monitored. Ten patients were hospitalized for fluid overload 25 times over 20.7±8.4 months. Intrathoracic impedance decreased before each admission by an average of 12.3±5.3% (P<0.001) over an average of 18.3±10.1 days. Impedance reduction began 15.3±10.6 days (P<0.001) before the onset of worsening symptoms. There was an inverse correlation between intrathoracic impedance and pulmonary capillary wedge pressure (r=−0.61, P<0.001) and between intrathoracic impedance and net fluid loss (r=−0.70, P<0.001) during hospitalization. Automated detection of impedance decreases was 76.9% sensitive in detecting hospitalization for fluid overload, with 1.5 false-positive (threshold crossing without hospitalization) detections per patient-year of follow-up. Conclusions—Intrathoracic impedance is inversely correlated with pulmonary capillary wedge pressure and fluid balance and decreased before the onset of patient symptoms and before hospital admission for fluid overload. Regular monitoring of impedance may provide early warning of impending decompensation and diagnostic information for titration of medication.

Reversal of left ventricular remodeling by synchronous biventricular pacing in heart failure

Synchronous biventricular pacing is a new nonpharmacological supplemental treatment of advanced heart failure associated with electromechanical conduction delay. However, the role of pacing on left ventricular remodeling is unknown. Eleven patients with New York Heart Association Class III to IV heart failure, a left ventricular ejection fraction < 35%, and a QRS duration ≥ 140 ms received a biventricular dual chamber pacemaker. Serial echocardiography, 6‐minute hall walk, and Minnesota Living with Heart Failure quality‐of‐life (QOL) questionnaire were performed before and after up to 3 months of pacing. At 3 months there was a significant increase in fractional shortening (P < 0.001), ejection fraction (P < 0.001), and cardiac output (P < 0.05). The left ventricular end‐diastolic volume (245 ± 70 vs 185 ± 37 mL, P < 0.05), end‐systolic volume (209 ± 69 vs 140± 44 mLP < 0.05), and mitral regurgitation were reduced (P < 0.05), and diastolic filling time was lengthened (P < 0.05). There were also improvements in heart failure symptoms, an increase in 6‐minute walk distance, and a decrease in QOL scores. Synchronous biventricular pacing for 3 months was associated with hemodynamic improvements, reversal of left ventricular remodeling, and increase in left ventricular systolic function, and a decrease in secondary mitral regurgitation.

PROGRAMMED ATRIAL SENSITIVITY : A CRITICAL DETERMINANT IN ATRIAL FIBRILLATION DETECTION AND OPTIMAL AUTOMATIC MODE SWITCHING

Automatic mode switching (AMS) prevents tracking of paroxysmal atria] fibrillation (AF) in dual chamber pacing. The correct detection of AF can be affected by the programmed atrial sensitivity (AS). We prospectively studied the relationship between AS, AF under‐sensing, an d AMS, using unfiltered bipolar in tracardiac atrial electrogram s recorded from 17 patients during sinus rhythm (SR) and in AF. Overall, 780 rhythms were recorded and replayed onto three dual chamber pacemaker models using different AMS algorithms (Thera DR 7940, Marathon DDDB 294–09, and Meta DDDH 1254), and the ventricular responses were measured. AS was randomly programmed in steps from the highest available AS to half of the mean atrial P wave amplitude (PWA), and the percentage of appropriate AMS responses (defined as a ventricular pacing rate at the expected AMS mode) were recorded. AMS efficacy was related to the programmed AS settings in an exponential manner. At low AS settings, a higher percentage of tests were associated with absence of, or with intermittent AMS and tracking of AF, whereas at higher AS, oversensing of noise during SR occurred. An optimal AS measured approximately 1.3 mV, representing about one‐third of the PWA measured during SR, although oversensing of SR and undersensing of AF continued to occur in 14% of tests and time, respectively, due to the high variation in PWA during AF. Thus, a fixed AS cannot eliminate AF undersensing without inviting noise oversensing, suggesting the need for automatic adjustments of AS, or the use of a rate‐limiting algorithm to prevent rate oscillation during intermittent AF sensing. In conclusion, AMS functions of existing pacemakers were significantly limited by the undersensing of AF and oversensing of noise. Proper adjustment of the AS is important to enable effective AMS during AF.

Impacts of ventricular rate regularization pacing at right ventricular apical vs. septal sites on left ventricular function and exercise capacity in patients with permanent atrial fibrillation

AIMS The deleterious effects of right ventricular apex (RVA) pacing may offset the potential benefit of ventricular rate (VR) regularization during atrial fibrillation (AF). Recent studies suggested that right ventricular septal (RVS) pacing may prevent the potential deleterious effects of RVA pacing and enhance the VR regularization (VRR) with ventricular pacing due to closer proximity of the pacing site to the retrograde atrioventricular conduction. METHODS AND RESULTS We randomized 24 patients with permanent AF and symptomatic bradycardia to undergo RVA (n = 12) or RVS (n = 12) pacing. A VRR algorithm was programmed for all patients at 6-month after implantation. All patients underwent 6 min hall walk (6MHW) to assess exercise capacity at 6, 12, and 24 months, and radionuclide ventriculography to determine left ventricular ejection fraction (LVEF) at 6 and 24 months. Baseline characteristics were comparable in both groups except pacing QRS duration was significantly shorter during RVS pacing than RVA pacing (132 +/- 4 vs. 151 +/- 6 ms, P = 0.012). In both groups, VRR significantly increased the percentage of ventricular pacing and reduced VR variability (P < 0.05) without increasing mean VR (P > 0.05). At 6 months, 6MHW and LVEF were comparable in patients with RVA and RVS pacing (P > 0.05). At 24 months, patients with RVA pacing had significant decreases in LVEF and 6MHW after VRR pacing (P < 0.05), whereas RVS pacing with VRR preserved LVEF and improved 6MHW (P < 0.05). CONCLUSION In patients with permanent AF, VRR pacing at RVS, but not at RVA, preserves LVEF and provides incremental benefit for exercise capacity.

Angiographic and clinical implications of combined ST-segment elevation in anterior and inferior leads in acute myocardial infarction.

The clinical and angiographic findings of patients suffered from acute myocardial infarction (MI) and presented with combined ST elevation in both anterior and inferior leads remain unclear.

A Comparative Study on the Behavior of Three Different Automatic Mode Switching Dual Chamber Pacemakers to Intracardiac Recordings of Clinical Atrial Fibrillation

Automatic mode switching (AMS) allows patients with dual chamber pacemakers who develop paroxysmal AF to have a controlled ventricular rate. The aim of this study was to (1) compare the rate‐controlled behavior of three AMS algorithms in response to AF, in terms of speed and stability of response and resynchro‐nization to sinus rhythm, and (2) compare the influence of pacemaker programming on optimal mode switching. We studied 17 patients (12 men, 5 women; mean age 59 ± 15 years) who developed AF during electrophysiological study. Unfiltered bipolar atrial electrograms during sinus rhythm and AF were recorded onto high fidelity tapes and replayed into the atrial port of three dual chamber pacemakers with different mode switching algorithms (Them, Marathon, Meta). The Thera pacemaker uses rate smoothing, and mode switches occur when mean sensed atrial rate exceeds the predefined AMS rate (MR). Marathon mode switches after a programmable number of consecutive rapid atrial events (NR). Meta DDDR monitors the atrial rate by a counter for atrial cycles faster than the programmed AMS rate. It increases or decreases the counter if the atrial cycle length is shorter or longer than the programmed AMS interval, respectively. Mode switch occurs when the AF detection criteria are met (CR). A total of 260 rhythms were studied. NR was significantly faster than MR and CR (latency 2.5 ± 3 svs 26 ± 7 s vs 15 ± 22 s, respectively, P < 0.0001). During sustained AF, MR resulted in the most stable and regular ventricular rhythm compared to NR or CR. In CR, ventricular rate oscillated between AMS and atrial tracking (cycle length variations: 44 ± 2 s vs 346 ± 109 s vs 672 ± 84 s, P < 0. 05). At resumption of sinus rhythm, MR resyn‐chronized after 143±22 s versus 3.4 ± 0.7 s for NR and 5.9 ± 1.1 s for CR, resulting in long periods of A V dissociation when a VVI/VV1R mode is used after AMS. Programming of atrial refractory periods did not affect AMS response, although the speed of AMS onset can be adjusted by programming of onset criteria in the Meta DDDR. AMS algorithms differ in their ability to handle recorded clinical atrial arrhythmias. The rapid‐responding algorithm exhibits rate instability, whereas slow responding algorithm shows a long delay in response and risk of AV dissociation. Thus different instrumentation of AMS may have clinical implications in patients with dual chamber pacemakers who develop AF.

Control of paroxysmal atrial fibrillation recurrence using combined administration of propafenone and quinidine

The frequent recurrence of paroxysmal atrial fibrillation (PAF) despite the use of standard antiarrhythmic agents prompted the use of new therapeutic approaches. There are few data on systematic assessment of PAF control with stepwise dose escalation and the use of a drug combination. Low-dose quinidine may promote the efficacy of propafenone by inhibiting its degradation through the cytochrome P450 pathway (CYP2D6). We prescribed propafenone 300 to 450 mg/day to 60 patients with PAF for 8 weeks, and 62% were symptomatically controlled. The 19 refractory patients were randomized in a double-blinded fashion to receive either a higher dose of propafenone (450 to 675 mg/day) or the standard dose of propafenone with low-dose quinidine 150 mg/day, each for an 8-week study period, and subsequently crossed over to the alternative treatment. The resulting serum propafenone concentrations were 259 +/- 208 and 336 +/- 237 mg/day (p >0.5), respectively. Both treatment arms prolonged the time to the first symptomatic atrial fibrillation (AF) recurrence and the interval between attacks, and AF was controlled in 37% of patients. However, the higher dose of propafenone was associated with gastrointestinal side effects not present with the low-dose quinidine combination. Of the 10 refractory patients, 7 were further controlled with a standard dose of propafenone plus quinidine (600 mg/day). Overall, control of PAF was achieved in 85% of patients at the end of 8 months; adverse effects necessitating withdrawal were observed in 6%, and uncontrolled AF in 5% of patients. There was no difference in the mean AF rate during recurrences in all phases, and ventricular proarrhythmia was not seen. This study documents the role of stepwise antiarrhythmic treatment of PAF. The use of a standard dose of propafenone, followed by low-dose quinidine combination to reduce propafenone degradation, and the combined standard dose of propafenone and quinidine may be used to maximize efficacy and tolerability.