Minimizing right ventricular pacing: a new paradigm for cardiac pacing in sinus node dysfunction

Indications for permanent pacing in dogs and cats

Pacemaker implantation is considered as a standard procedure for treatment of symptomatic bradycardia in both dogs and cats. Advanced second-degree and third-degree atrioventricular blocks, sick sinus syndrome, persistent atrial standstill, and vasovagal syncope are the most common rhythm disturbances that require pacing to either alleviate clinical signs or prolong survival. Most pacemakers are implanted transvenously, using endocardial leads, but rarely epicardial leads may be necessary. To decide whether a patient is a candidate for pacing, as well as which pacing modality should be used, the clinician must have a clear understanding of the etiology, the pathophysiology, and the natural history of the most common bradyarrhythmias, as well as what result can be achieved by pacing patients with different rhythm disturbances. The goal of this review was, therefore, to describe the indications for pacing by evaluating the available evidence in both human and veterinary medicine. We described the etiology of bradyarrhythmias, clinical signs and electrocardiographic abnormalities, and the choice of pacing modality, taking into account how different choices may have different physiological consequences to selected patients. It is expected that this review will assist veterinarians in recognizing arrhythmias that may require permanent pacing and the risk-benefit of each pacing modality and its impact on outcome.

Apical ballooning syndrome (takotsubo cardiomyopathy) after permanent dual-chamber pacemaker implantation

Apical ballooning syndrome, also called takotsubo cardiomyopathy, has been recently reported. It may mimic acute myocardial infarction and is typically observed in postmenopausal women after stressful events. A 75-year-old female after permanent dual chamber pacemaker implant complained of chest pain with repolarization alterations suggesting acute myocardial ischemia. Echocardiography showed a left ventricle with akinesia of the apical portions and reduced global systolic function. The patient was treated with antithrombotic agents and intravenous nitrates. No coronary lesions were found at angiography. At ventriculography, a typical takotsubo-like shape of the left ventricle was observed. The clinical and echocardiographic picture normalized at discharge.

Clinical observations with Closed Loop Stimulation pacemakers in a large patient cohort: the CYLOS routine documentation registry (RECORD)

AIMS

Closed Loop Stimulation (CLS) pacemakers couple pacing rate to myocardial contraction dynamics by monitoring unipolar right ventricular impedance on a beat-to-beat basis. The aim of this large-scale registry was to evaluate the safety and efficacy of the CLS therapy under clinical routine conditions.

METHODS AND RESULTS

A total of 706 patients was enrolled in the clinical investigation 'Registry: CYLOS Routine Documentation' (RECORD) at 57 investigational sites in Europe and Hong Kong. Not to interfere with clinical routine and therapeutic decisions of health care providers, the registry was implemented as a part of the standard follow-up schedule. Two follow-ups were conducted within 12 months of enrolment in order to evaluate typical programming of CLS-related parameters, reasons for their later reprogramming, frequency of patient intolerance to CLS, and physicians' satisfaction with medical benefits and technical performance of CLS in each patient. The investigators' medical and technical notes on CLS rated it excellent in ~80% of patients, poor in 1.4% (medical benefit) or 0.5% (technical performance), and adequate in rest of the patients. Closed Loop Stimulation functionality was not influenced by pacing site variation within the right ventricle (septal, outflow tract) or by advanced heart failure (New York Heart Association classes II-IV). Permanent or temporary CLS deactivation was undertaken for various reasons in 6.2% of patients. Signs of intolerance to CLS or rate-adaptive pacing were reported by 2.3% of patients. Reprogramming of CLS-related parameters was seldom undertaken, with >90% of pacemakers operating with default settings in the long term.

CONCLUSION

Clinical performance of CLS was very satisfactory in the large cohort studied.

Cardiac remodeling with rhythm versus rate control strategies for atrial fibrillation in patients with heart failure: insights from the AF-CHF echocardiographic sub-study

BACKGROUND

In patients with heart failure and atrial fibrillation, the AF-CHF (Atrial Fibrillation and Congestive Heart Failure) trial did not demonstrate the superiority of rhythm control (RhyC) over a rate control (RaC) strategy on cardiovascular mortality. Nevertheless, deleterious hemodynamic effects of atrial fibrillation can lead to further decrease in left ventricular (LV) function and progression of symptoms. This echocardiographic sub-study was designed to compare the effects of the two treatment strategies on LV ejection fraction (LVEF), chamber volumes and dimensions, valvular regurgitation and functional status.

METHODS AND RESULTS

A total of 59 patients (29 RhyC, 30 RaC) aged 67±8 years (14% women), enrolled in the AF-CHF trial at the Montreal Heart Institute underwent standardized echocardiograms at baseline and at 12 months. Mean LVEF at baseline was severely depressed (RhyC: 27.0±4.9% and RaC: 27.6±7.4%, p=0.73), and improved to a similar degree in both groups (RhyC: +8.0±10.4% and RaC: +4.5±10.6, both p<0.05; p=0.19 for RhyC versus RaC). Other echocardiographic parameters, such as LV end-systolic volume index and degree of mitral and tricuspid regurgitation, remained unchanged. New York Heart Association functional class and distance walked in 6 min improved significantly in both groups (RhyC: +48.9±78.7 m and RaC: +47.2±96.7 m, both p≤0.01), with no difference between RhyC and RaC strategies.

CONCLUSIONS

Improvements in LVEF and functional status are observed after 12 months in patients with heart failure and atrial fibrillation, regardless of whether rate or rhythm control strategies are used.

Right ventricular apical pacing: the unwanted model of cardiac stimulation?

Despite having a huge benefit in enabling heart rate control, cardiac pacing by stimulating the right ventricular apex causes an artificial iatrogenic left bundle-branch block-like syndrome. As a result, QRS widening and cardiac wall desynchronization occurs. The problems caused by this undesirable pacemaker side effect have been ignored, as they are counteracted by the great benefit of cardiac rate correction. However, the compelling evidence about its harmful effect presented in this article cannot be disregarded and should start an attitude change toward alternate sites of ventricular pacing and preclusion of the right ventricular apex stimulation.

Choosing pacemakers appropriately

The range of implantable cardiac pacing devices has expanded, with the advances in available technology. Indications for cardiac pacing devices, that is pacemakers, implantable cardioverter defibrillators (ICDs) and cardiac resynchronisation therapy devices (CRTs), have expanded for the treatment, diagnosis and monitoring of bradycardia, tachycardia and heart failure. While the need for pacemakers is increasing, not all patients who require pacemakers are receiving them, especially in the Asia-Pacific region. There is a need to be more critical in advising the use of more expensive devices like ICDs and CRT/CRT-D devices, since most patients in the Asia-Pacific region pay out of pocket for these therapies. The AHA-ACC guidelines need not be blindly followed, since they are too wide-sweeping and are often based on the intention-to-treat basis of trials rather than on the parameters of the patients actually enrolled.