Max Schaldach

Intramyocardial Electrogram Variability in the Monitoring of Graft Rejection After Heart Transplantation

The ventricular evoked response is a well‐standardized electrophysiological signal that can be used for noninvasive, long‐term cardiac transplant monitoring. Rejection‐sensitive and infection‐specific parameters extracted from intramyocardial electrograms correlate with clinical results. The influences of pacing rate, transition from intrinsic to paced rhythm and positional changes on the diagnostic parameters were studied. Increasing the pacing rate shortened the ventricular evoked response and directly influenced the infection specific parameter. The rejection‐sensitive parameter remained stable at pacing rates between 100 and 120 beats/min. Measurements made immediately after the patient assumed a supine position and after switching to paced rhythm showed a decrease in the rejection‐sensitive parameter. A change in position from supine to upright did not influence the rejection‐sensitive parameter, but higher values were measured after returning to the supine position. In conclusion, noninvasive recordings of the ventricular evoked response for monitoring of cardiac allograft should be done at the same time of day, at the same pacing rate, and with the patient resting for at least 5 minutes before measurements are made.

Dynamic cardiomyoplasty: long-term clinical results in patients with dilated cardiomyopathy.

BACKGROUND Dynamic cardiomyoplasty has been considered to be an effective method of surgical treatment of patients with end-stage heart failure, and is an alternative to heart transplantation. METHODS We critically evaluated the long-term course of 52 patients with dilated cardiomyopathy who underwent dynamic cardiomyoplasty and were followed-up for up to 110 months. RESULTS Dilated cardiomyopathy was due to undetermined cause in 42 patients (80.8%), Chagas disease in 8 (15.4%), viral infection in 1 (1.9%), and peripartum cardiomyopathy in 1 (1.9%). In the nonchagasic group the survival rates were 79.5% +/- 6.1%, 67.8% +/- 7.1%, 53.7% +/- 8.3%, 49.9% +/- 8.3%, 14.9% +/- 12.2%, and 14.9% +/- 12.2%, respectively, at 12, 24, 48, 60, 80 and 110 months of follow-up. In the chagasic patients the survival rates were 37.5% +/- 17.1%, 12.5% +/- 11.7%, 12.5% +/- 11.7% and 0%, respectively, at 12, 24, 48, and 60 months of follow-up, making chagasic cardiomyopathy a possible contraindication for dynamic cardiomyoplasty. CONCLUSIONS There was no correlation between the clinical improvement and hemodynamic data. Ventricular fibrillation was a frequent cause of immediate and late death, suggesting the need for prophylactic use of antiarrhythmic drugs or implantable cardioverter/ defibrillators.

Optimizing the Geometry of Implantable Leads for Recording the Monophasic Action Potential with Fractally Coated Electrodes

This study investigates the influence of various lead geometry on intracardial signals like the monophasic action potential (MAP) to optimize the geometry of implantable MAP leads. The experimental results were compared with a field theoretical approach to the origin of MAP from the transmembrane potential (TAP). During the experiments several lead geometries (tip surface: 1.3 to 12 mm2; tip‐ring distance: 0.8 mm to 25 cm; ring surface: 1.8mm2 to 40 mm2) were investigated in endo‐ and epicardial positions in 12 dogs (17±9 kg). The electrodes were fixed passively (tines) or actively (screws). MAP was recorded during several interventions and correlated with MAP measured using an Ag‐AgCl MAP catheter. The experimental results showed that small tips provided high MAP amplitudes with less pressure. No difference was observed using active and passive fixations. A tip‐ring distance smaller than 5 mm with a ring surface smaller than the tip (<5 mm2) avoided artifacts in the repolarization course. For the theoretical approach the quasistatic, anisotropic bidomain model was calculated in smalt unity volumes Vi where the TAP φm was constant and represented by the current density J. Two solutions for electrode positions at and outside the heart were achieved. By superposition of each solution φei the summed potential at the electrode position was calculated. The theoretical findings show in good correlation with the experimental results that a larger distance than 10 mm leads to distortions in repolarization course by signals proportional to φout.

SIMULTANEOUS RECORDINGS OF THE MONOPHASIC ACTION POTENTIAL WITH SILVER CHLORIDE- AND IR-COATED ELECTRODES

Ag AgCI and Ir‐coated electrodes allow the recording of the monophasic action potential (MAP) due to their electrical properties like non‐polarisability. This study investigates the correlation of MAP recorded with both types of electrodes. In 20 mongrel dogs (18 ± 6 kg) an Ag/AgCI and an Ir‐coated catheter (Ir) were placed endo‐cardially in the apex of the right ventricle. The effects of isoproterenol and verapamil were investigated during spontaneous rhythm and stimulation simultaneously recorded with both types of electrodes in 10 dogs without AV‐node ablation. The correlation at different heart rates were investigated in 10 other dogs with complete AV‐block. The morphology and amplitudes of MAP were comparable (AgCl: 15±7 mV; Ir: 13±8 mV). Following an i.v. bolus of 2μg/kg isoproterenol the spontaneous rate increased (175±18 to 245±25 bpm). During stimulation with 250 ms cycle length the duration shortened (MAPd90: AgCl: 160 ± 11 to 130 ± 12 ms; Ir: 154 ± 18 to 128±15 ms). The alterations reversed after 20 mm. An i.v. bolus of 0.2 mg/kg verapamil decreased the spontaneous rate (167±11 to 104 ± 23 bpm) and lengthened the MAPd90 (AgCl: 182 ± 14 to 220±13 ms; Ir: 174 ± 16 to 216, 21 ms) at 300 ms stimulation. The correlation between the MAPd90 of both lead types was r=0.98 during all measurements. Under the effect of beta‐agonist and Ca2+ ‐antagonist medication MAP showed a strong correlation recorded with both types of electrodes. Thus, both leads allow the recording of MAP but only the Ir‐electrodes with their long‐term stability are implantable and allows us to control the effects of drugs with implantable devices.

Development of a New Hybrid Coronary Stent Design with Optimized Biocompatible Properties

Coronary artery disease (CAD) remains the most common cause of death in industrialized countries, despite steady progress in treatment and prevention. Besides drug therapy, a significant advance in the treatment of CAD has been the introduction of coronary artery bypass grafting (CABG) (1,2). In particular, the use of arteries, instead of veins, has resulted in excellent success rates (3–5).

Ventricular evoked response in patients with hypertrophic obstructive cardiomyopathy treated with DDD pacing

OBJECTIVE To assess the changes in ventricular evoked responses (VER) produced by the decrease in left ventricular outflow tract gradient (LVOTG) in patients with hypertrophic obstructive cardiomyopathy (HOCM) treated with dual-chamber (DDD) pacing. METHODS A pulse generator Physios CTM (Biotronik, Germany) was implanted in 9 patients with severe drug-refractory HOCM. After implantation, the following conditions were assessed: 1) Baseline evaluation: different AV delay (ranging from 150 ms to 50 ms) were sequentially programmed during 5 to 10 minutes, and the LVOTG (as determined by Doppler echocardiography) and VER recorded; 2) standard evaluation, when the best AV delay (resulting in the lowest LVOTG) programmed at the initial evaluation was maintained so that its effect on VER and LVOTG could be assessed during each chronic pacing evaluation. RESULTS LVOTG decreased after DDD pacing, with a mean value of 59 +/- 24 mmHg after dual chamber pacemaker, which was significantly less than the gradient before pacing (98 + 22 mmHg). An AV delay > 100 ms produced a significantly lower decrease in VER depolarization duration (VERDD) when compared to an AV delay < or = 100 ms. Linear regression analyses showed a significant correlation between the LVOTG values and the magnitude of VER (r = 0.69; p < 0.05) in the 9 studied patients. CONCLUSION The telemetry obtained intramyocardial electrogram is a sensitive means to assess left ventricular dynamics in patients with HOCM treated with DDD pacing.

MARCAPASSO COM SENSOR DE CONTRATILIDADE REGULADO PELAS VARIACOES DO SISTEMA NERVOSO AUTONOMO NA MIOCARDIOPATIA CHAGASICA CRONICA

OBJETIVO: Analisar o desempenho da estimulacao cardiaca artificial com marcapasso do tipo VVIR cujo sensor e regulado pelas variacoes do sistema nervoso autonomo em pacientes chagasicos com disturbio no sistema de conducao. METODOS: Estudados 47 chagasicos, 28 do sexo masculino, com idades entre 24 e 68 anos, 36 tinham bloqueio atrioventricular (AV) total; 8, bloqueio AV de 2o grau 2; e 3 doenca do nodulo sinusal, e encontravam-se, de acordo com a NYHA, em classe I (4), II (15), III (16) e IV (12). Apos o implante de marcapasso do tipo VVIR os pacientes foram acompanhados durante 12 meses. A resposta de frequencia foi registrada em gravacoes de Holter de 24h e divididos em dois grupos de acordo com a FC em repouso - grupo 1: >65bpm e grupo 2: £65bpm, para estudo comparativo, considerando: 1) FC em exercicio no periodo de pos-implante; 2) PA em repouso apos o implante e 3) avaliacao dos grupos de eletrodos identificados como TIR-60-UP e outros eletrodos. RESULTADOS: O grupo 1 teve em exercicio menor variacao entre seus valores, do que o grupo 2, indicando que esse tipo de sistema de estimulacao permite controlar individualmente cada paciente. Os valores de PA em repouso e em exercicio nao foram diferentes entre os grupos. O eletrodo do tipo TIR-60-UP, comportou-se como os demais eletrodos. CONCLUSAO: O marcapasso do tipo VVIR cujo sensor e regulado pelas variacoes do SNA propicia o restabelecimento dos mecanismos fisiologicos em chagasicos, sendo que 74% deles tiveram melhora de uma ou duas classes funcionais da NYHA.PURPOSE To analyse the performance of the artificial cardiac stimulation with the VVIR pacemaker whose sensor is adjusted by the variations of the autonomic nervous system in Chagas disease patients with deficiency of the conduction system. METHODS Forty-seven Chagas disease patients have been studied, 28 male between 24 and 68 years old, 36 patients had complete AV block, 8 had 2nd degree AV block and the other 3 had sinusnode disease. The patients were in class I (4), II (15), III (16) and IV (12) according to the NYHA. A 12-month-follow-up with constant clinical evaluations was carried out after pacemaker implantation. Patients were divided in 2 different groups according to the HR at rest--group 1: > 65 beats per minute (bpm) and group 2: < or = 65 bpm, for a comparative study considering: 1) HR at stress test after the implantation; 2) arterial blood pressure at rest after the implantation and, 3) evaluation of the identified electrodes such as TIR-60-UP and others. RESULTS The group 1 had greater HR at rest, and a smaller variation of values at stress than group 2. This shows that with this type of stimulation system it is possible to control each patient separately. The values of blood pressure at rest and during stress were not different between groups. According to the factors analysed the TIR-60-UP electrode had the same performance as the others. CONCLUSION The VVIR pacemaker with the sensor adjusted by the ANS variations has provided the Chagas patients with a restoration of their physiological mechanisms. 74% of them had the improvement of either one or 2 functional classes.

Estimulação DDD com eletrodo único usando estimulação atrial bifásica simultânea: primeiros resultados clínicos

Single lead, dual chamber (DDD) pacing with an atrial floating electrode is limited by high atrial capture thresholds. We evaluated a new atrial stimulation lead with two atrial ring electrodes on a single lead and overlapping unipolar square wave pulses of an opposite polarity. The first pulse is applied to the distal electrode and is positive, the second pulse is to the proximal electrode and is negative, both with respect to the pacemaker housing. The delay between the two pulses is programmable between 0.0 ms to 1.0 ms. The distance between the atrial electrode rings is 10 mm and the distance from the distal atrial ring to the unipolar ventricular electrode can be selected to be 11, 13 or 15 cm. The positioning of the atrial ring is selected according to the measured overlapping biphasic pulse thresholds, including respiratory maneuvers to confirm continuous capture/sensing. The pulse generator has a single lead connection and the capability of delivering the two atrial square wave opposite programmable pulses, with delays from 0.0 to 1.0 ms. The generator may be programmed to the single lead unipolar VDD mode. This system was implanted in 4 patients with complete AV block with normal sinus mode fuction. Atrial and diaphragmatic thresholds for various pulse configurations, widths and delays were measured intra and postoperatively. The midportion of RA was selected as the best location for the atrial rings with continuous capture during deep inspiration. The intra and postoperative (48hrs) measurements were: Threshold Intra-op POstop. (48hrs) Atrial unipolar 3.2 + 0.47 V not measurable Atrial (overlapping biphasic) 1.6 + 0.37 V 3.37 + 0.84 V Diaphragmatic above 7 V 5.21 + 0.3 V wave sensing 2.35 + 1.3 mV 1.27 + 0.8 mV The patients were discharged in the VDD mode. Evaluation thirty days after showed transient loss of atrial capture during inspiration in one patient in spite of absence of other threshold changes compared to the 48 hours evaluation. In conclusion, overlapping biphasic stimulation reduces the atrial pacing thresholds while maintaining adequate atrial sensing with a safe margin regarding diaphragmatic stimulation.

Cardiomioplastia: novo gerador da Biotronic

In the cardiomyoplasty, the contraction of the skeleton muscle, undergone electric stimulation on the dilated ventricle wall, increases the ventricle function, which is dependent of the heart and the base disease previous conditions. One of the main problems which interferes with the sucess of the cardiac muscle replacement is the myocardial synchronic stimulation and the skeleton muscle. The stimulation of this muscle in long-term has been possible because of the special electrodes associated with the sequential progressive stimulation, adjusting it to the cardiac function, through the gradual transformation of glicolitic fibers exposed to fatigue in highly resistant slow oxidizers. The pulse generator Myos (Biotronik) has been used in our center for electrical stimulation of the latissimus dorsalis in synchronization with the myocardium. This electronic circuit and lithium battery type of cardiomyostimulator stores a stimulation program responsible for different operational modes, adapted by acomputer program. In order to program the cardiomyostimulator, the moment of the pulse synchronization with the aortic valve opening is extremely important. The high velocity M mode is utilized to evaluate the synchronism. The cardiomyoplasty clinical evaluation is based on the results obtained from 32 patients at 22 ti 72 years old (average=46.2 years) most of patients (72%) presented dilated myocardiopathy due to undetermined cause, 24% of chagasic origin, 3% virus and 3% due to peripartum. Hospital and late mortality rate were both 12.5% and 3.1% and 3.7% respectively, excluding the chagasic patients. The actuarial survival was 81.3 + - 0.22% after 6 years and 94.4 + - 0.1 % after 5 years, withdrawing the chagasic patients. The average indexes of systolic diameters (55,1 mm), diastolic (70,7 mm), segmental shortening (22.8%) and ejection fraction (51.0%), related to an average follow-up of 14.2 months, reflect that the cardiomyoplasty can be effective to assist the left ventricle. Choosing the right patient seems to be key to the goog operative result in short and long terms.