A possible mechanism for pacemaker-induced T-wave changes

Evaluation of Long Term Effect of RV Apical Pacing on Global LV Function by Echocardiography

INTRODUCTION

We very often face pacemaker implanted patients during follow-up with shortness of breath and effort intolerance inspite of normal clinical parameters.

AIM

The aim of our study is to evaluate the cause of effort intolerance and probable cause of sub-clinical Congestive Cardiac Failure (CCF) in a case of long term Right Ventricular (RV) apical pacing on global Left Ventricular (LV) function non- invasively by echocardiography.

MATERIALS AND METHODS

We studied 54 patients (Male 42, Female 12) of complete heart block (CHB) with RV apical pacing (40 VVI and 14 DCP). Mean duration of pacing was 58+4 months. All patients underwent 24 hours Holter monitoring to determine the percentage of ventricular pacing beats. 2-D Echocardiography was done to assess the regional wall motion of abnormality and global LV ejection fraction by modified Simpson's rule. These methods were coupled with the Doppler derived Myocardial Performance Index (MPI), tissue Doppler imaging, and mechanical regional dyssynchrony with 3-D Echocardiography. Data were analysed from 54 RV- apical paced patients and compared with age and body surface area of 60 controlled subjects (Male 46, Female 14).

RESULTS

Evaluation of LV function in 54 patients demonstrated regional wall motion abnormality and Doppler study revealed both LV systolic and diastolic dysfunction compare with control subjects (regional wall motion abnormality 80±6% vs 30±3% with p-value<0.0001) which is proportional to the percentage of ventricular pacing beats (mean paced beat 78%). Global LVEF 50±4% vs 60±2% (p-valve <0.0001) and MPI 0.46 ±0.12 v/s 0.36±0.09 (p-value <0.0001).

CONCLUSION

RV-apical pacing induces iatrogenic electrical dyssynchrony which leads to remodeling of LV and produces mechanical dyssynchrony which is responsible for LV dysfunction. Alternate site of RV pacing and/or biventricular pacing should be done to maintain biventricular electrical synchrony which will preserve the LV function.

Repolarization changes underlying long-term cardiac memory due to right ventricular pacing: noninvasive mapping with electrocardiographic imaging

BACKGROUND

Cardiac memory refers to the observation that altered cardiac electrical activation results in repolarization changes that persist after the restoration of a normal activation pattern. Animal studies, however, have yielded disparate conclusions, both regarding the spatial pattern of repolarization changes in cardiac memory and the underlying mechanisms. The present study was undertaken to produce 3-dimensional images of the repolarization changes underlying long-term cardiac memory in humans.

METHODS AND RESULTS

Nine adult subjects with structurally normal hearts and dual-chamber pacemakers were enrolled in the study. Noninvasive electrocardiographic imaging was used before and after 1 month of ventricular pacing to reconstruct epicardial activation and repolarization patterns. Eight subjects exhibited cardiac memory in response to ventricular pacing. In all subjects, ventricular pacing resulted in a prolongation of the activation recovery interval (a surrogate for action potential duration) in the region close to the site of pacemaker-induced activation from 228.4±7.6 ms during sinus rhythm to 328.3±6.2 ms during cardiac memory. As a consequence, increases are observed in both apical-basal and right-left ventricular gradients of repolarization, resulting in a significant increase in the dispersion of repolarization.

CONCLUSIONS

These results demonstrate that electrical remodeling in response to ventricular pacing in human subjects results in action potential prolongation near the site of abnormal activation and a marked dispersion of repolarization. This dispersion of repolarization is potentially arrhythmogenic and, intriguingly, was less evident during continuous right ventricular pacing, suggesting the novel possibility that continuous right ventricular pacing at least partially suppresses pacemaker-induced cardiac memory.

Assessment of right and left ventricular perfusion in patients with right bundle branch block

BACKGROUND

Patients with conduction abnormalities may have abnormal images on perfusion scintigraphy without evidence of coronary artery disease (CAD). Based on the presence of left ventricular perfusion abnormalities in left bundle branch block and taking advantage of the Tc-99m sestamibi for the assessment of myocardial perfusion of both ventricles, we aimed to evaluate right (RV) and left (LV) myocardial perfusion in patients with right bundle branch block (RBBB).

METHODS

This study included 21 patients with RBBB and 21 control subjects without conduction abnormality. None had previous myocardial infarction, known CAD, left ventricular hypertrophy, LVEF <55%, congenital, pulmonary or valvular heart disease. Rest and stress SPECT images were obtained using 1-d Tc-99m sestamibi SPECT protocol. Regional perfusion of LV and RV myocardium was semiquantitatively evaluated. Also, RV/LV uptake ratio was calculated in two different ways.

RESULTS

In patients with RBBB, the normality ratios of RV and LV myocardial perfusion were very high (both 90.5%) and not different from those of patients with normal intraventricular conduction. In the comparison of RV/LV uptake ratios, no significant difference was found between the RBBB and control groups.

CONCLUSIONS

LV perfusion, RV perfusion or R-to-L perfusion ratio were not significantly influenced by the conduction abnormality in this selected patient population with RBBB. Tc-99m sestamibi myocardial scintigraphy could help in the exclusion of myocardial ischemia in patients with RBBB.

Regional myocardial blood flow in patients with sick sinus syndrome randomized to long-term single chamber atrial or dual chamber pacing--effect of pacing mode and rate

OBJECTIVES

This study aimed to evaluate regional myocardial blood flow (MBF) and global left ventricular ejection fraction (LVEF) during chronic pacing in patients with sick sinus syndrome (SSS) randomized to either single chamber atrial (AAI) or dual chamber (DDD) pacing.

BACKGROUND

Experimental studies indicate that chronic pacing in the right ventricular apex changes regional MBF, thereby compromising left ventricular function.

METHODS

Thirty patients (age 74 +/- 10 years) were randomized to AAI (n = 15) or DDD (n = 15) pacemakers. After 22 +/- 7 months of pacing, MBF was quantified with 13N-labeled ammonia positron emission tomography scanning at 60 beats per min and 90 beats per min. Patients in the DDD group furthermore underwent MBF measurement at temporary AAI pacing, 60 beats per min. Myocardial blood flow was assessed in the anterior, lateral, inferior and septal regions, and the global mean MBF was calculated. Left ventricular ejection fraction was determined by echocardiography at pacemaker implantation and at the time of MBF measurements.

RESULTS

Myocardial blood flow at rates 60 and 90 beats per min did not differ between the AAI and DDD groups. During temporary AAI pacing in the DDD group, MBF was significantly higher than during DDD pacing in both the inferior (p = 0.001) and septal (p = 0.004) regions and also globally (0.61 +/- 0.15 vs. 0.53 +/- 0.13 mL x g(-1) x min(-1), p = 0.005). In the DDD group, LVEF decreased from pacemaker implantation to time of MBF measurements (0.61 +/- 0.09 vs. 0.56 +/- 0.07, p = 0.013). Left ventricular ejection fraction during temporary AAI pacing at time of MBF measurements was not different from LVEF at pacemaker implantation.

CONCLUSIONS

In patients with SSS, chronic DDD pacing reduced inferior, septal and global mean MBF as well as LVEF, as compared with temporary AAI pacing. The LVEF reversed to baseline level during temporary AAI pacing despite 22 months of permanent ventricular pacing preceding it. Augmenting pace rate to 90 beats per min increased MBF equally in the two treatment groups.

Long-term effect of right ventricular pacing on myocardial perfusion and function

OBJECTIVES

The purpose of this study was to investigate the effect of long-term ventricular pacing on myocardial perfusion and function in patients receiving such pacing.

BACKGROUND

The long-term effect of ventricular pacing on myocardial perfusion and function in humans is unclear, although animal studies have suggested that it may be adverse.

METHODS

Forty-three patients with complete heart block and dual-chamber rate-adaptive (DDDR) pacing were studied. All underwent thallium-201 (Tl-201) exercise myocardial scintigraphy to assess myocardial perfusion and radionuclide ventriculography to determine left ventricular function and regional wall motion. Coronary angiography was also performed in patients with abnormal findings on Tl-201 study.

RESULTS

There was no significant difference in mean age, gender, percent ventricular pacing, pacing threshold, ventricular pacing output and metabolic equivalents on exercise testing between patients with or without perfusion defects on exercise Tl-201 scintigraphy. However, the duration of pacing tended to be longer in patients with than in those without perfusion defects (43.9 +/- 49.7 vs. 20.1 +/- 9.8 months, p = 0.05). Tl-201 perfusion defects were noted in 28 (65%) of 43 of patients (inferior 78% [n = 22], apical 67% [n = 17], septal 21% [n = 6], anterior 7% [n = 2], lateral 3% [n = 1)]. Of 16 of 28 patients with abnormal Tl-201 findings who underwent coronary angiography, only 3 (19%) had significant coronary artery disease. Patients with an abnormal perfusion defect had a significantly lower left ventricular ejection fraction (48.5 +/- 9.9% vs. 59.6 +/- 8.9%, p < 0.001) and a higher percent of wall motion abnormalities (57% vs. 20%, p = 0.026), mainly over apical regions.

CONCLUSIONS

Long-term right ventricular apical pacing resulted in a high incidence of myocardial perfusion defects that increased with the duration of pacing. These myocardial perfusion abnormalities were associated with apical wall motion abnormalities and impaired global left ventricular function.

Electrocardiographic evidence of ischemia during ventricular paced rhythms

Exercise-induced electrocardiographic (ECG) changes are the most widely recognized noninvasive means for detecting myocardial ischemia. The specificity of these changes depends on the normalcy of the resting ECG. Right ventricular pacing produces major QRS and ST-T changes very similar to those of complete left bundle-branch block. They alter the resting ECG such that ischemic changes are considerably difficult to detect. Because of these resting abnormalities, ECG changes during treadmill exercise testing usually do not facilitate the diagnosis of ischemia or coronary artery disease. The following are two cases of ischemic ECG changes that occurred during right ventricular pacing. To our knowledge, there have been no reports of the classic ECG changes of ST-segment depression suggestive of ischemia which occurred during right ventricular pacing and which were discernible from the resting ECG changes.