The acute effect of atrioventricular pacing on sympathetic nerve activity in patients with normal and depressed left ventricular function

When Sinus Tachycardia Becomes Too Much: Negative Effects of Excessive Upright Tachycardia on Cardiac Output in Vasovagal Syncope, Postural Tachycardia Syndrome, and Inappropriate Sinus Tachycardia

BACKGROUND

Upright posture reduces venous return, stroke volume, and cardiac output (CO) while causing reflex sinus rate (heart rate [HR]) increase. Yet, in inappropriate sinus tachycardia (IST), postural tachycardia syndrome (POTS), and vasovagal syncope (VVS), symptomatic excessive HR occurs. We hypothesized that CO reaches maximum as function of HR in all.

METHODS

We recruited 12 healthy controls, 9 IST, 30 VVS, and 30 POTS patients (13-23years) selected randomly by disorder not by HR, each fulfilled appropriate diagnostic criteria. Subjects were instrumented for electrocardiography, beat-to-beat blood pressure, respiratory rate, CO-Modelflow algorithm, and central blood volume from impedance cardiography; 10-minute data were collected supine; subjects were tilted head-up for ≤10 minutes. We computed phase differences, ΔΦ, between fluctuations of HR (ΔHR) and CO (ΔCO) tabulating data when phases were synchronized, determined by a squared nonlinear phase synchronization index >0.5, describing extent/validity of CO/HR coupling. We graphed results supine, 1-minute post-tilt-up, mid-tilt, and pre-tilt-down using polar coordinates (HR-radius, ΔΦ-angle) plotting cos(ΔΦ) versus HR to determine if transition HR exists at which in-phase shifts to antiphase above which CO decreases when HR further increases.

RESULTS

At baseline HR, diastolic and mean arterial pressures in IST and POTS were higher versus controls. Upright HR increased most in POTS then IST and VVS, with diverse changes in CO, SVR, and central blood volume. Each patient grouping was separately and collectively analyzed for HR change showing transition from in-phase to anti-phase (ΔΦ) as HR increased: HRtransition=115±6 (IST), 123±8 (POTS), 124±7 (VVS), P=ns. Controls never reached transitional HR.

CONCLUSIONS

Excessive HR independently and equivalently reduces upright CO, in IST, POTS, and VVS.

Effect of increasing heart rate on finger photoplethysmography fitness index (PPGF) in subjects with implanted cardiac pacemakers

Finger photoplethysmography (PPG) is a noninvasive method that measures blood volume changes in the finger. The PPG fitness index (PPGF) has been proposed as an index of vascular risk and vascular aging. The objectives of the study were to determine the effects of heart rate (HR) on the PPGF and to determine whether PPGF is influenced by blood pressure (BP) changes. Twenty subjects (78±8 years, 3 female) with permanent cardiac pacemakers or cardioverter defibrillators were prospectively recruited. HR was changed by pacing, in a random order from 60 to 100 bpm and in 10 bpm increments. At each paced HR, the PPGF was derived from a finger photoplethysmogram. Cardiac output (CO), stroke volume (SV) and total peripheral resistance (TPR) were derived from the finger arterial pressure waveform. Brachial blood pressure (BP) was measured by the oscillometric method. This study found that as HR was increased from 60 to 100 bpm, brachial diastolic BP, brachial mean BP and CO were significantly increased (p<0.01), whilst the PPGF and SV were significantly decreased (p<0.001). The effects of HR on the PPGF were influenced by BP, with a decreasing HR effect on the PPGF that resulted from a higher BP. In conclusion, HR was a significant confounder for PPGF and it must be taken into account in analyses of PPGF, when there are large changes or differences in the HR. The magnitude of this effect was BP dependent.

P-Wave Amplitude and PR Changes in Patients With Inappropriate Sinus Tachycardia: Findings Supportive of a Central Mechanism

BACKGROUND

The mechanism of inappropriate sinus tachycardia (IST) remains incompletely understood.

METHODS AND RESULTS

We prospectively compared 3 patient groups: 11 patients with IST (IST Group), 9 control patients administered isoproterenol (Isuprel Group), and 15 patients with cristae terminalis atrial tachycardia (AT Group). P-wave amplitude in lead II and PR interval were measured at a lower and higher heart rate (HR1 and HR2, respectively). P-wave amplitude increased significantly with the increase in HR in the IST Group (0.16±0.07 mV at HR1=97±12 beats per minute versus 0.21±0.08 mV at HR2=135±21 beats per minute, P=0.001). The average increase in P-wave amplitude in the IST Group was similar to the Isuprel Group (P=0.26). PR interval significantly shortened with the increases in HR in the IST Group (146±15 ms at HR1 versus 128±16 ms at HR2, P<0.001). A similar decrease in the PR interval was noted in the Isuprel Group (P=0.6). In contrast, patients in the atrial tachycardia Group experienced PR lengthening during atrial tachycardia when compared with baseline normal sinus rhythm (153±25 ms at HR1=78±17 beats per minute versus 179±29 ms at HR2=140±28 beats per minute, P<0.01).

CONCLUSIONS

We have shown that HR increases in patients with IST were associated with an increase in P-wave amplitude in lead II and PR shortening similar to what is seen in healthy controls following isoproterenol infusion. The increase in P-wave amplitude and absence of PR lengthening in IST support an extrinsic mechanism consistent with a state of sympatho-excitation with cephalic shift in sinus node activation and enhanced atrioventricular nodal conduction.

Optimal Cardiac Resynchronization Therapy Pacing Rate in Non-Ischemic Heart Failure Patients: A Randomized Crossover Pilot Trial

Background

The optimal pacing rate during cardiac resynchronization therapy (CRT) is unknown. Therefore, we investigated the impact of changing basal pacing frequencies on autonomic nerve function, cardiopulmonary exercise capacity and self-perceived quality of life (QoL).

Methods

Twelve CRT patients with non-ischemic heart failure (NYHA class II–III) were enrolled in a randomized, double-blind, crossover trial, in which the basal pacing rate was set at DDD-60 and DDD-80 for 3 months (DDD-R for 2 patients). At baseline, 3 months and 6 months, we assessed sympathetic nerve activity by microneurography (MSNA), peak oxygen consumption (pVO₂), N-terminal pro-brain natriuretic peptide (p-NT-proBNP), echocardiography and QoL.

Results

DDD-80 pacing for 3 months increased the mean heart rate from 77.3 to 86.1 (p = 0.001) and reduced sympathetic activity compared to DDD-60 (51±14 bursts/100 cardiac cycles vs. 64±14 bursts/100 cardiac cycles, p<0.05). The mean pVO₂ increased non-significantly from 15.6±6 mL/min/kg during DDD-60 to 16.7±6 mL/min/kg during DDD-80, and p-NT-proBNP remained unchanged. The QoL score indicated that DDD-60 was better tolerated.

Conclusion

In CRT patients with non-ischemic heart failure, 3 months of DDD-80 pacing decreased sympathetic outflow (burst incidence only) compared to DDD-60 pacing. However, Qol scores were better during the lower pacing rate. Further and larger scale investigations are indicated.

Trial Registration

ClinicalTrials.gov NCT02258061

Increase in paced heart rate reduces muscle sympathetic nerve activity in heart failure patients treated with cardiac resynchronization therapy

AIMS

To test the hypothesis that acute increased biventricularly (BiV) paced heart rate (pHR) results in decreased muscle sympathetic nerve activity (MSNA), and that dyssynchronous pacing (AAI) attenuates this effect, in heart failure patients receiving cardiac resynchronization therapy (CRT).

METHODS AND RESULTS

Fourteen CRT patients (NYHA II-III, 12 males, mean EF 28 ± 14%) were recruited. Three different pHRs (50-90 b.p.m.) were randomly programmed in BiV- and AAI-pacing modes. Muscle sympathetic nerve activity (total sympathetic nerve activity/min (units) and number of bursts/100 RR) were recorded from the peroneal nerve using a microelectrode. In addition, cardiac output (CO) and mean blood pressure (mBP) were measured. With BiV pacing, the total MSNA/min was lower at 70 b.p.m. (-7 ± 21%, P = 0.18) and 90 b.p.m. (-29 ± 18%, P = 0.01) compared with at 50 b.p.m. (280 ± 180 U). Similarly, bursts/100RR decreased with increased BiV pHR. Cardiac output (3.7 L/min at 50 b.p.m., +12 ± 12% at 70 b.p.m., and +18 ± 19% at 90 b.p.m.) and mBP (78 ± 11 mmHg at 50 b.p.m., +6 ± 6% at 70 b.p.m. and +11 ± 8% at 90 b.p.m.) increased significantly at elevated pHRs in BiV-pacing mode. The effect on MSNA, CO, and mBP was less pronounced in AAImode but we found no significant differences between the pacing modes.

CONCLUSION

Increased pHR acutely reduces MSNA and improves haemodynamics in HF patients treated with CRT with no evident differences between BiV- and AAI-pacing modes. Further studies are warranted to guide the programming of basic pHR in CRT patients.