K. Bachmann

Effects of magnetic resonance imaging on cardiac pacemakers and electrodes

In phantom studies we investigated the effects of magnetic resonance imaging (MRI) on pacemakers and electrodes. Twenty-five electrodes were exposed to MRI in a 1.5T scanner with continuous registration of the temperature at the electrode tip. Eleven pacemakers (five single chamber and six dual chamber) were exposed to MRI. Pacemaker output was monitored to detect malfunction in VOO/DOO and VVI/DDD modes. A temperature increase at the electrode tip of up to 63.1 degrees C was observed during 90 seconds of scanning. In seven electrodes the temperature increase exceeded 15 degrees C. Although no pacemaker malfunctions were observed in asynchronous pacing mode (VOO/DOO), inhibition and rapid pacing were observed during spin-echo imaging if the pacemakers were set to VVI or DDD mode. Pacemaker function was not impaired during scanning with gradient-echo sequences. Next to pacemaker dysfunction, electrode heating has to be considered a possible adverse effect when exposing patients with pacemakers to MRI.

Noninvasive, Three-Dimensional Visualization of Coronary Artery Bypass Grafts by Electron Beam Tomography

Electron beam tomography (EBT, ultrafast computed tomography [CT], cine CT) combines unique temporal and high spatial resolution and is especially well suited for cardiac imaging. We established and evaluated a protocol for the noninvasive visualization and assessment of aortocoronary artery bypass grafts. Twenty-five patients with 56 bypass grafts were studied by EBT. Forty contiguous cross-sectional images were acquired triggered to the electrocardiogram during breathhold and intravenous injection of contrast agent. Three-dimensional reconstructions of the heart and bypass grafts were performed and compared with selective angiography of the bypass grafts. In 1 patient with 2 bypass grafts, a technically inadequate EBT examination was obtained. In the remaining patients (54 grafts), all 13 bypass occlusions were diagnosed with a sensitivity and specificity of 100%. Evaluation for hemodynamically relevant stenosis was possible in 84% of cases (36 of 43 patent grafts) and yielded a sensitivity of 100% (5 of 5 high-grade stenoses correctly detected) and specificity of 97% (1 false-positive diagnosis of high-grade graft stenosis). The main reasons for impaired ability to evaluate the scans were breathing artifacts and misplacement of the imaging volume, causing parts of the bypass grafts to be cut off. EBT permits noninvasive determination of bypass graft occlusion and relevant stenosis with high accuracy.

Usefulness of respiratory gated magnetic resonance coronary angiography in assessing narrowings ≥50% in diameter in native coronary arteries and in aortocoronary bypass conduits

Magnetic resonance coronary angiography (MRCA) is a promising method for the assessment of proximal coronary artery stenosis. Conventional 2-dimensional techniques require repetitive breath holds to image multiple sections. This may lead to misregistrations if the respiratory level is not exactly reproduced. In the present study, MRCA was performed using a 3-dimensional approach with navigator echo-based respiratory gating. In 73 patients (55 men and 18 women) who were referred for cardiac catheterization, the assessment of significant stenoses (> or = 50%) was performed in the proximal and midsegments of the coronary arteries after multiplanar reconstruction of the visualized coronary arteries. In addition, in 8 patients with coronary artery bypass grafts the patency of the transplants was evaluated. After withdrawing 8 patients from analysis because of poor image quality, stenosis evaluation was possible in 236 of 455 reviewed coronary segments (52%). In the other 219 cases, either the visualization of the vessel segment was indistinct (30%) or the segment was located outside the imaging volume (18%). In total, 28 of 43 significant coronary stenoses could be correctly identified (65%). Evaluation of bypass graft patency was possible in 7 patients. All 4 occluded and 13 of 15 patent grafts were correctly classified. Thus, respiratory gated MRCA is a feasable method for the assessment of hemodynamically significant coronary stenoses and bypass graft patency. However, technical improvements are mandatory to improve accuracy of the method.

Congenital Myocardial Sympathetic Dysinnervation (CMSD)—A Structural Defect of Idiopathic Long QT Syndrome

Concerning the path genetic mechanism of idiopathic long QT syndrome (LQTS), the hypothesis of a specific sympathetic imbalance has gained general acceptance, but its validity has never been proven. To test this hypothesis I‐123‐MIBG, an analogue of norepinephrine and guanethi‐dine, was used to provide scinfigraphic display of the efferent cardiac sympathetic innervation. Twelve members of four LQTS families fmean age 38.2 ± 17.2 years, eight males) and eight healthy volunteers (mean age 48.2 ± 13.3 years, five males) were studied by means of M23‐MTBG single photon emission computed tomography (SPECT). A quantitative analysis of all scans was performed. All scans of the healthy volunteers show a uniform tracer uptake with sometimes slightly decreased activity in the apex. (1) All patients with QTc > 440 msec (n = 5); (2) all, who had suffered from at least one episode of torsade de pointes, ventricular fibrillation (VF) or syncope (n = 5); and (3) all symptomatic patients with QTc prolongation (n = 4) have reduced or abolished (P < 0.02) MIBG uptakes in the inferior and inferior septal parts of the left ventricle (congenital myocardial sympathetic disintegration [CMSD]). Additionally, one female without symptoms or QTC prolongation (LQT) shows an abnormal MIBG SPECT similar to the one of her daughter, who has LQT and symptoms. One male without LQT, who had suffered from VF shows CMSD similar to his father, who has LQT, but no symptoms. All members of the families with normal MIBG SPECTs have neither LQT nor symptoms. In all families CMSD fulfills the criteria of autonomic‐dominant inheritance. Normal QTc‐interval predicted only in 57% normal cardiac sympathetic enervation in the present LQTS families. Therefore, quantitative I‐123‐MIBG SPECT enables to identify myocardial sympathetic disintegration as structural defect in LQTS. CMSD is associated with and without LQT and presents a pattern of autosomal‐dominant inheritance. LQT at rest or during exercise was specific (100%). but less sensitive (63%) in the assessment of CMSD than I‐123‐MIBG SPECT.

Detection of High-Grade Restenosis After PTCA Using Contrast-Enhanced Electron Beam CT

BACKGROUND Contrast-enhanced electron beam computed tomography (EBCT) has been shown to permit noninvasive visualization of the coronary arteries. We determined the value of EBCT to noninvasively detect high-grade restenosis after percutaneous transluminal coronary angioplasty (PTCA). METHODS AND RESULTS Fifty patients (37 to 68 years of age), were investigated by EBCT at a mean interval of 9 months after PTCA of coronary artery stenoses. Forty axial cross-sections of the heart (3-mm slice thickness, 1-mm overlap) were acquired triggered to the ECG after intravenous injection of contrast agent. Three-dimensional reconstructions of the coronary arteries were rendered with a lower threshold of 80 HU to selectively visualize the contrast-enhanced vessel lumen. EBCT results were compared with conventional quantitative coronary angiography (QCA) performed within 1 week. In 6 patients, the PTCA segment could not be evaluated because of impaired image quality. Sixteen of the remaining 44 patients had high-grade restenoses in QCA (>70% diameter reduction), which was correctly detected by EBCT in 15 cases (94% sensitivity). There were 5 false-positive EBCT results of high-grade restenosis (82% specificity). CONCLUSIONS EBCT with intravenous injection of contrast agent permits the noninvasive diagnosis of restenosis after PTCA, with high sensitivity and sufficient specificity.

Evaluation of the non-invasive localization accuracy of cardiac arrhythmias attainable by multichannel magnetocardiography (MCG)

The accuracy of multichannel magnetocardiography (MCG) for the non-invasive localization of cardiac arrhythmias was investigated. A non-magnetic catheter was used in phantom studies and for cardiac pacing of 6 patients. In a clinical setting, 32 patients with WPW-syndrome, 37 patients with premature ventricular complexes and 12 patients with ventricular tachycardia were studied and the MCG results compared to reference methods, including invasive electrophysiological mapping.Phantom and pacing studies demonstrated the spatial localization accuracy to be better than 15 mm for a dipole-to-dewar distance below 15 cm. In all patients with structural cardiac disease, the ectopic focus was localized at the margin of the damaged area, serving as a proof of MCG localization. Invasive mapping confirmed the MCG result whenever performed (42 patients). In 11 patients (9 WPW, 2 VT) the MCG localization result was verified by successful HF catheter ablation as a gold standard.MCG permits the non-invasive localization of cardiac arrhythmias with high spatial accuracy. MCG guided HF catheter ablation constitutes a new concept of non-invasive localization and minimally invasive causal therapy.

Pränatale Registrierung fetaler Herzaktionen mit Magnetokardiographie

Das fetale Magnetokardiogramm (fMKG) mißt das vom fetalen Herzen erzeugte magnetische Feld. Im Gegensatz zum fetalen EKG gelingt mit fMKG die nichtinvasive Registrierung des PQRST-Erregungsablaufes. So kann die Dauer der fetalen Herzzeitintervalle in verschiedenen Schwangerschaftsstadien bestimmt werden. Unsere Arbeitsgruppe führte 104 magnetokardiographische Messungen bei 53 Patientinnen ab der 10. Schwangerschaftswoche (SSW) durch (1–10 Messungen pro Patientin) Das fMKG wurde mit einem 37-Kanal-Meßsystem in einer magnetisch abgeschirmten Kammer registriert, wobei der Meßkopf berührungsfrei 2–3 cm über dem mütterlichen Abdomen positioniert wurde (Abtastfrequenz 1024 Hz, Bandbreite 1–200 Hz). Die Registrierung fetaler Herzaktionen gelang mit einem standardisierten Meßprotokoll ab der 20./21. SSW. In Einzelfällen ließen sich bereits in der 16. SSW Herzaktionen ableiten. Mit zunehmendem fetalem Wachstum verlängerte sich die Dauer der Herzzeitintervalle. Im Beobachtungszeitraum verlängerte sich die P-Welle im Mittel von 31 auf 49 ms (p < 0,05), das PQ-Intervall von 95 auf 107 ms (n.s.), der QRS-Komplex von 36 auf 52 ms (p < 0,01). Die Höhe der Amplituden des fMKG nahm mit zunehmendem Gestationsalter zu. Mit fMKG ist zudem eine Analyse pränataler Arrhytmien möglich. Bei 20 Feten (26.–38. SSW) wurden z.T. komplexe ventrikuläre und supraventrikuläre Arrhytmien oder Erregungsüberleitungsstörungen registriert und klassifiziert. Dank seines hohen Auflösungsvermögens offeriert das fMKG zusätzliche, mit den etablierten Verfahren wie Kardiotokographie oder fetale Doppler-Echokardiographie nicht verfügbare Informationen über die fetale Herzaktivität. Das fMKG könnte daher das diagnostische Sprektrum in der Schwangerschaftsvorsorge erweitern. Fetal magnetocardiography (fMCG) registers the magnetic field generated by the fetal heart. In contrast to the fetal elctrocardiogram, fECG permits non-invasive registration of fetal heart activity and documentation of all parts of the PQRST-wave-forms from the second trimenon onwards. This facilitates the determination of cardiac time intervals and establishment of reference values for different stages of pregnancy. We examined 53 women in 104 recordings from the 10th week of gestation onwards (1 to 10 recordings per individual). The fMCG (37 magnetic channels, sampling rate 1024 Hz, bandwidth 1–200Hz) was recorded non-invasively over the mothers abdomen in a magnetically shielded room. Registration of fetal heart beats was generally successful from the 20/21th week of gestation onwards. In a few cases, fetal heart beats could be registered as early as in the 16th week. Cardiac time intervals and amplitudes of fMCG increased concordantly with fetal growth. Mean P wave duration increased from 31 to 49 ms (p < 0.05), PQ interval from 95 to 107 ms (n. s.) and QRS duration from 36 to 52 ms (p < 0.01). The mean amplitudes of the P and R waves also increased. FMCG, furthermore permits a prenatal diagnosis of fetal cardiac arrhythmias. We recorded fetal arrhythmias in 20 cases (26–38th week), including episodes of ventricular and supraventricular arrhythmias or atrioventricular blockings. Due to its high resolution, fMCG offers new information on the development of fetal cardiac activity which cannot be achieved by conventional methods like cardiotocography or dopplerultrasound. Therefore, fMCG could become a new diagnostic instrument for monitoring fetal wellbeing during pregnancy.

Visualization of the coronary arteries in three-dimensional reconstructions using respiratory gated magnetic resonance imaging.

Objective To assess the applicability of respiratorygated magnetic resonance coronary angiography, combined with three-dimensional image reconstruction, for visualizing the coronary arteries.Methods Twenty subjects (three healthy volunteers and 1 7 patients without stenoses detected by coronary angiography) were investigated. Magnetic resonance imaging was performed in a 1.5 T scanner using ECG-tnggered gradient-echo sequences to acquire a volume data set consisting of 24–48 contiguous axial cross-sections of the heart (2 mm slice thickness, 1.17 mm x 1.1 7 mm in-plane resolution). Navigator-echo-based retrospective respiratory gating was used to minimize respiratory motion artifacts. Three-dimensional reconstructions of the heart were rendered using surface-display techniques. The length of the visualized coronary arteries was measured in curved multiplanar reconstructions.Results In the three-dimensional reconstructions, the left main artery (LMA) and left anterior descending artery (LADA) were visualized in 1 7 cases, the left circumflex artery (LCXA ) in 15, and the right coronary artery (RCA) in 16 cases. Vessel continuity was uninterrupted in all 1 7 cases for the LMA, in 14 for the LADA, eight for the LCXA, and 13 for the RCA. The mean lengths of the visualized vessels were 14 ± 7 mm for the LMA, 65 ± 13 mm for the LADA, 45 ± 1 6 mm for the LCXA, and 37 ± 26 mm for the RCA. Reasons for impaired visibility of the LCXA and RCA were poor image quality due to there being a low contrast: noise ratio, motion artifacts, and incomplete coverage by the imaging volume.Conclusions Navigator-echo-based magnetic resonance imaging is a promising technique for investigating the coronary arteries. Acquisition of a volume data set permits three-dimensional displays of the coronary vessels.

Risk of endocarditis in transesophageal echocardiography

The risk of endocarditis associated with transesophageal echocardiography was studied in 101 patients. To evaluate possible bacteremia, blood cultures were performed on samples from consecutive patients who did not have clinical or laboratory evidence of infection. The broth blood culture Signal system was used in all patients, and additionally, the lysis-centrifugation technique was performed in a subgroup of 40 patients to further ameliorate recovery of rapidly phagocytosed germs. Comprehensive criteria for differentiation between true bacteremia and possible contamination were provided by means of simultaneous blood sampling from two separate venipuncture sites and skin specimens from the venipuncture area. Oropharyngeal specimens were cultured for evaluation of possible association of oropharyngeal flora with positive blood culture findings. They revealed facultative pathogenic isolates, as well as physiologic residental flora, in 15 patients. All blood isolates that were recovered simultaneously 6 minutes after the procedure were found to be sterile. Correspondingly, clinical follow-up for 2 weeks was uneventful with regard to episodes of infection. These results indicate that the risk of bacteremia associated with transesophageal echocardiography is extremely low. Thus endocarditis prophylaxis is not required for this procedure.

Clinical magnetocardiography: Experience with a biomagnetic multichannel system

The magnetic fields caused by the human hearts electrical activity were coherently recorded with a biomagnetic multichannel system (KRENIKON®) during 1 to 10 minutes in 49 patients. 31 to 37 magnetic channels were recorded simultaneously with the ECG and respiration.Comparison of a magnetic index and the Sokolow-Lyon index to echocardiographic findings in the quantification of left ventricular hypertrophy demonstrated the superiority of the magnetocardiogram (MCG) as compared to the ECG. The magnetocardiographic investigation of patients with WPW-Syndrome, ventricular extrasystoles, ventricular tachycardia, and paced ventricular beats demonstrated that multichannel magnetocardiography permits the non-invasive three dimensional localization of arrhythmogenic tissue with high spatial accuracy.