Electrical modulation of cardiac contractility: clinical aspects in congestive heart failure

[Cardiac contractility modulation]

Heart failure (HF) will be one of the biggest medical challenges in the coming years, with increasing prevalence in an aging society. It is associated with a poor prognosis and impaired quality of life-despite steadily improving medical therapy which has resulted in a steady decrease in mortality and an increase in quality of life. In medically refractory patients with impaired left ventricular (LV) function, left bundle branch block and wide QRS complex (≥130 ms) cardiac resynchronization therapy (CRT) in addition to medical therapy has become the gold standard. Additionally, other therapeutic modalities such as vagal stimulation are being clinically tested but as yet have no general therapeutic recommendation. Overall, CRT patients represent only one-third of all HF patients and about 25% are "non-responders" who do not benefit from CRT.In HF patients with an LVEF between 25 and 45% and a QRS duration <130 ms who are not suitable for CRT, cardiac contractility modulation (CCM) is currently a therapeutic option that has been shown in several randomized trials to be efficacious and safe. It reduces the frequency of HF hospitalizations and improves HF symptoms, functional capacity, and quality of life. The goal of this article is to present mechanisms of action, major clinical studies, current indications, and recent developments of CCM for the treatment of patients with chronic HF.

Four-year follow-up of a patient with mixed cardiomyopathy and an implanted cardiac contractility modulation device: a case report

The article presents a case report of a 28-year-old male patient with mixed dilated cardiomyopathy: myocardial noncompaction and chemotherapy-related cardiotoxicity, which led to severe heart failure (HF). With optimal drug therapy, the patient was implanted with a cardiac contractility modulation device in order to improve exercise tolerance, quality of life and relieve HF symptoms. Complex therapy has led to significant clinical and echocardiographic improvement. This case demonstrates a 4-year follow-up of a patient with a reduced left ventricular ejection fraction and an implanted cardiac contractility modulation device, whose condition, after several severe HF decompensations, was stabilized.

Cardiac Contractility Modulation in Patients with Heart Failure with Reduced Left Ventricular Ejection Fraction

Cardiac contractility modulation is an innovative therapy conceived for the treatment of heart failure. It is a device-based therapy, employing multiple electrodes to deliver relatively high-voltage (~7.5 V) biphasic signals to the endocardium of the right ventricular septum, in order to improve heart failure symptoms, exercise capacity and quality of life. Multiple clinical and mechanistic studies have been conducted to investigate the potential usefulness of this technology and, as of now, they suggest that it could have a place in therapy and meet a relevant medical need for a specific sub-category of underserved heart failure patients with reduced left ventricular ejection fraction. More studies are needed to further investigate its effect on outcomes such as mortality and rate of hospitalizations.

Possibilities and perspectives of using cardiac contractility modulation in patients with chronic heart failure and atrial fibrillation

Heart failure is one of the main health care problems all over the world. Although, there are many drugs with proven effectiveness and hi-tech devices, there is a continuous process of searching new possibilities in heart failure prophylaxis going on because of huge economic burden and impact on life quality. Developing of atrial fibrillation in heart failure patients increases the risks of hospitalization and all-cause mortality. Appearance of new Optimizer Smart® system of cardiac contractility modulation is a perspective way of treatment in patients with heart failure and atrial fibrillation, who are not a candidate or have not got a good result from cardiac resynchronization therapy (CRT).

Clinical effects of cardiac contractility modulation (CCM) as a treatment for chronic heart failure

Cardiac contractility modulation (CCM) signals are non-excitatory signals applied during the absolute refractory period that have been shown to enhance the strength of left ventricular contraction without increasing myocardial oxygen consumption in studies carried out in animals and humans with heart failure and reduced ejection fraction. Studies from myocardial tissue of animals and humans with heart failure suggest that the mechanisms of these effects is that CCM drives expression of many genes that are abnormally expressed in heart failure towards normal, including proteins involved with calcium cycling and the myocardial contractile machinery. Clinical studies have primarily focused on patients with normal QRS durations in view of the fact that cardiac resynchronization (CRT) is a viable option for patients with prolonged QRS duration. These studies show that CCM improves exercise tolerance as indexed by peak oxygen consumption (VO(2)) and quality of life indexed by the Minnesota Living with Heart Failure Questionnaire. The device is currently available for clinical use in countries recognizing the CE mark and is undergoing additional testing in the USA under a protocol approved by the Federal Drug Administration.

Electrical stimulation of the gut for the treatment of type 2 diabetes: the role of automatic eating detection

BACKGROUND

Automatic eating detection (AED) can potentially support treatments that need to be synchronized with food intake. This article analyzes an implantable AED device working in conjunction with gastric stimulation intended to treat type 2 diabetes (T2DM). The device continuously senses for changes in tissue impedance and electrical activity induced by food intake and initiates treatment sessions upon detection. This article reviews AED performance as well as its relevance to treatment outcomes.

METHODS

Obese T2DM (n = 12) were implanted with gastric leads and the TANTALUS device. An AED algorithm was embedded in the device and was used to initiate periods of electrical stimulation during food intake. AED performance was assessed using patients' food diaries. The treatment outcome at 37 weeks postimplants was correlated with the rates of stimulation during large meals vs stimulation during periods of no caloric intake.

RESULTS

The algorithm was able to detect 73% of meals consumed while sensing. The rate of false stimulations was 28%. Stimulation during meals was significantly correlated (R(2) = 0.45, p < 0.05) with hemoglobin A1c change (average drop in hemoglobin A1c was -1 +/- 0.4%) but not with changes in body weight (average drop -4.7 +/- 2.8 kg). Stimulation during periods with no caloric intake was negatively correlated with hemoglobin A1c reduction (R(2) = 0.27, p < 0.05).

CONCLUSIONS

Sensing of gastric activity can be used for detection of food intake. The synchronization of gastric stimulation to periods of food intake is correlated with metabolic outcomes. AED may also benefit other applications such as drug delivery and control of food restriction devices.

Enhanced inotropic state of the failing left ventricle by cardiac contractility modulation electrical signals is not associated with increased myocardial oxygen consumption

BACKGROUND

Previous studies in patients and in dogs with experimentally induced heart failure (HF) showed that electrical signals applied to the failing myocardium during the absolute refractory period improved left ventricular (LV) function. We examined the effects these same cardiac contractility modulating (CCM) electrical signals on myocardial oxygen consumption (MVO(2)) in both patients and dogs with chronic HF.

METHODS AND RESULTS

Six dogs with microembolizations-induced HF and 9 HF patients underwent CCM leads and generator (OPTIMIZER II) implantation. After baseline measurements, CCM signals were delivered continuously for 2 hours in dogs and for 30 minutes in patients. MVO(2) was measured before and after CCM therapy. In dogs, CCM therapy increased LV ejection fraction at 2 hours (26 +/- 1 versus 31 +/- 2 %, P = .001) without increasing MVO(2) (257 +/- 41 versus 180 +/- 34 micromol/min). In patients, CCM therapy increased LV peak +dP/dt by 10.1 +/- 1.5 %. As with dogs, the increase in LV function after 30 minutes of CCM therapy was not associated with increased MVO(2) (13.6 +/- 9.7 versus 12.5 +/- 7.2 mL O(2)/min).

CONCLUSIONS

The study results suggest that unlike cAMP-dependent positive inotropic drugs, the increase in LV function during CCM therapy is elicited without increasing MVO(2).

Electrical stimulation as treatment for obesity and diabetes

The prevalence of obesity is growing, is driving an increase in the prevalence of diabetes, and is creating a major public health crisis in the United States. Lifestyle and behavior therapy rarely give durable weight loss. There are few medications approved for the treatment of obesity. Those that exist are limited in efficacy and using them in combination does not result in greater weight loss. Surgical treatments for obesity are effective and give durable weight loss, but are accompanied by measurable morbidity and mortality. Several pacing approaches are being tried and are an outgrowth of pacing for gastroparesis. The Transcend(R) pacemaker blocks vagal efferents and delays gastric emptying, giving a 40% loss of excess body weight, if certain screening procedures are employed. The Tantulus pacemaker is still in development but increases antral muscular contractions and delays gastric emptying by stimulation during the absolute refractory period. Weight loss has been 30% of excess body weight, and glycohemoglobin decreased 1.6% in a trial of obese type 2 diabetes. Stimulation to the subdiaphragmatic sympathetics, vagal nerve stimulation with or without unilateral vagotomy, and intestinal pacing are other approaches that are still being evaluated preclinically. Clearly a safe, effective, and durable treatment for obesity is desperately needed. Electrical pacing of the gastrointestinal tract is promising therapeutically, and because pacemakers work through different mechanisms, combining pacemaker treatments may be possible. Rapid progress is being made in the field of electrical stimulation as a treatment for obesity and even greater progress can be expected in the foreseeable future.

Cardiac contractility modulation by non-excitatory currents: Studies in isolated cardiac muscle

BACKGROUND

Myocardial contractility can be altered using voltage clamp techniques by modulating amplitude and duration of the action potential resulting in enhanced calcium entry in the cell of isolated muscle strips (Non-Excitatory Currents; NEC). Extracellular electrical stimuli delivered during the absolute refractory period (Cardiac Contractility Modulation; CCM) have recently been shown to produce inotropic effects in-vivo.

AIM

Understanding the cellular mechanism, underlying the CCM effect, is essential for evaluating its clinical potential. We tested the hypothesis that NEC and CCM modulate contractility via similar cellular mechanisms.

METHODS

Square wave electric currents were applied in the organ bath to isometrically contracting rabbit RV papillary muscle and human failing trabecular muscle during the absolute refractory period (ARP).

RESULTS

These currents, which did not initiate new action potentials or contractions, modulated action potential duration (shortened or lengthened) and contractility (enhanced or depressed) in a manner that depended upon their amplitude, duration and delay from the pacing stimulus. The contractility modulation effect in the rabbit RV papillary muscle was markedly blunted after exposure to ryanodine, indicating that the sarcoplasmic reticulum plays an important role in the contractility modulation.

CONCLUSION

Like voltage clamping, extracellular currents applied during the ARP can similarly modulate action potential duration in-vitro and modulate myocardial contractility by similar intracellular mechanisms. This concept provides the potential of a therapeutic strategy in patients with heart failure to enhance contractility.

Electrical Signals Applied During the Absolute Refractory Period

Cardiac resynchronization therapy has been shown to be an effective treatment for patients with systolic ventricular dysfunction, prolonged (>120 ms) QRS duration, and New York Heart Association (NYHA) functional class III or IV symptoms despite optimal medical therapy. However, studies show that a majority of heart failure patients have QRS duration <120 ms. We have been investigating the potential utility of cardiac contractility modulating (CCM) signals as a treatment option for such patients. Cardiac contractility modulating signals are non-excitatory signals applied during the absolute refractory period using a pacemaker-like device that connects to the heart with pacemaker leads. Acute studies carried out in animals and humans with heart failure suggest that CCM signals can enhance the strength of left ventricular contraction. Results of initial long-term studies designed mainly to demonstrate feasibility and provide preliminary indication of safety in patients with medically refractory NYHA functional class III heart failure are summarized. The results of these preclinical and clinical studies formed the basis for proceeding with two prospective, randomized clinical studies currently underway to definitively test the safety and efficacy of this treatment.

Enhancement of antral contractions and vagal afferent signaling with synchronized electrical stimulation

Gastric filling activates vagal afferents involved in peripheral signaling to the central nervous system (CNS) for food intake. It is not known whether these afferents linearly encode increasing contractions of the antrum during antral distension (AD). The aim of this study was to investigate effects of AD and electrically enhanced antral contractions on responses of vagal afferents innervating the antrum. Single-fiber recordings were made from the vagal afferents in anesthetized male Long-Evans rats. Antral contractions were measured with a solid-state probe placed in the antrum. A nonexcitatory electrical stimulation (NES) inducing no smooth muscle contractions was applied during the ascending phase of antral contractions to enhance subsequent antral contractions. Fifty-six fibers identified during AD (1 ml for 30 s) were studied through different types of mechanical stimuli. Under normal conditions, one group of fibers exhibited rhythmic firing in phase with antral contractions. Another group of fibers had nonrhythmic spontaneous firing. Responses of 15 fibers were tested with NES during multiple-step distension (MSD). NES produced a mean increase in antral contraction amplitude (177.1 +/- 35.3%) and vagal afferent firing (21.6 +/- 2.6%). Results show that both passive distension and enhanced antral contractions activate distension-sensitive vagal afferents. Responses of these fibers increase linearly to enhanced antral contraction induced by NES or MSD up to a distending volume of 0.6 ml. However, responses reached a plateau at a distending volume >0.8 ml. We concluded that enhanced contraction of the antrum can activate vagal afferents signaling to the CNS.

Pacing techniques in heart failure: current concepts and future outlook

In addition to the well established benefits of traditional pacing methods, newer, left ventricular-based pacing techniques appear to induce significant hemodynamic improvements, benefit cardiac remodeling, improve functional capacity, and may decrease hospitalizations in appropriately selected patients with advanced systolic heart failure and intraventricular conduction defects. Encouraging results have been suggested from preliminary observational studies as well as from controlled clinical trials. Despite the generally positive outlook, much remains to be learned about multisite pacing techniques, appropriate site and patient selection, and long-term effectiveness.

Electric currents applied during refractory period enhance contractility and systolic calcium in the ferret heart

We investigated the mechanism of positive inotropism of electric currents applied during the absolute refractory period. Ten Langendorff-perfused ferret hearts were instrumented to measure isovolumic left ventricular pressure (LVP) and the aequorin luminescence. Biphasic square-wave electric currents (+/-20 mA, total duration 30 ms) were delivered between pairs of electrodes. Six hearts were perfused at different extracellular Ca(2+) concentrations ([Ca(2+)](o); 1, 2, 4, and 8 mM). These signals increased LVP from 50.0 +/- 9.4 to 70.1 +/- 14.7, from 67.5 +/- 11.0 to 79.0 +/- 15.6, from 79.3 +/- 21.0 to 87.1 +/- 22.8, and from 84.6 +/- 24.0 to 91.8 +/- 28.5 mmHg at the respective [Ca(2+)](o) (P < 0.05). Peak free intracellular [Ca(2+)] ([Ca(2+)](i)) increased from 0.52 +/- 0.13 to 1.37 +/- 0.23, from 0.76 +/- 0.23 to 1.73 +/- 0.14, from 1.10 +/- 0.24 to 2.05 +/- 0.33, and from 1.41 +/- 0.36 to 2.24 +/- 0.36 microM/ml, respectively (P < 0.001). With the use of 1 mg/l propranolol with 1 mM [Ca(2+)](o), LVP and [Ca(2+)](i) were increased significantly from 48.7 +/- 8.18 to 56.3 +/- 6.11 mmHg and from 0.61 +/- 0.11 to 1.17 +/- 0.20 microM, respectively (P < 0.05). In conclusion, positive inotropism of such electrical currents was due to increased peak [Ca(2+)](i) and Ca(2+) responsiveness of the myofilaments did not change significantly.

Current status and future expectations for multisite pacing in heart failure

The number of patients with congestive heart failure (CHF) has achieved astonishing proportions. It is a debilitating and usually lethal condition, aside from being responsible for an enormous proportion of health care expenditures. Advances in medical therapy have not been sufficient to significantly improve prognosis, and heart transplantation can only benefit a minority of patients. Biventricular pacing has emerged as a promising form of therapy for patients with severe, medical refractory CHF with ventricular conduction defects. However, there are many technical issues to be solved, and better methods of selecting patients who respond favorably to this form of therapy are yet to be developed. This article reviews the rationale, delivery modes, and available data supporting multisite cardiac pacing as an alternative form of therapy for the failing heart.

Cardiac contractility modulation by electric currents applied during the refractory period

Inotropic effects of electric currents applied during the refractory period have been reported in cardiac muscle in vitro using voltage-clamp techniques. We investigated how electric currents modulate cardiac contractility in normal canine hearts in vivo. Six dogs were instrumented to measure regional segment length, ventricular volume (sonomicrometry), and ventricular pressure. Cardiac contractility modulating (CCM) electric currents (biphasic square pulses, amplitude +/-20 mA, total duration 30 ms) were delivered during the refractory period between pairs of electrodes placed on anterior and posterior walls. CCM significantly increased index of global contractility (E(es)) from 5.9 +/- 2.9 to 8.3 +/- 4.6 mmHg/ml with anterior CCM, from 5.3 +/- 1.8 to 8.9 +/- 4.0 mmHg/ml with posterior CCM, and from 6.1 +/- 2.6 to 11.0 +/- 7.0 mmHg/ml with combined CCM (P < 0.01, no significant change in volume axis intercept). End-systolic pressure-segment length relations showed contractility enhancement near CCM delivery sites, but not remotely. Relaxation was not influenced. CCM increased mean aortic pressure, but did not change peripheral resistance. Locally applied electrical currents enhanced global cardiac contractility via regional changes in myocardial contractility without impairing relaxation in situ.