Hogne Engedal

Long-term comparison of unipolar and bipolar pacing and sensing, using a new multiprogrammable pacemaker system.

Over a six‐month period a comparison was made between uni‐ and bipolar myocardial stimulation thresholds and R‐wave sensitivity in 15 consecutive pacemaker patients. The patients received a new multiprogrammable Cordis 336 A pulse generator, that could be programmed with either uni‐ or bipolar circuitry. In addition, rale, output, sensitivity and pacing mode could be noninvasively programmed. The occurrence of myopotential interference at different sensitivity levels was also studied. Cordis 325–161 bipolar endocardial leads were used in all patients. In one patient, the current output sometimes had to be programmed higher bipolarly than unipolarly to capture the ventricles, otherwise no differences in threshold were found. Acutely, R‐wave sensitivity was superior in 9 patients (60%) in the bipolar mode. Unipolar and bipolar electrograms were equal in 4 (26.7%), whereas unipolar R‐wave sensitivity was best in only 2 (13.3%) of the patients. At a six‐month follow‐up, the same tendency was found. In 5 patients, bipolar sensing was superior to unipolar, while uni‐and bipolar sensitivily was equal in the remaining patients. Myopotential inhibition was never seen in the bipolar mode at highest sensitivity (0.8 mV) even during provocative tests (n = 35) or 24‐hour Holter monitoring (n = 12). In the unipolar mode, 14/15 patients (93.3%) showed inhibition during provocative tests and 12/32 patients (100%) during monitoring at a programmed sensitivity of 0.8 mV. No patients had myopotential inlerference at a sensitivity level of 3.5 mV. All patients have theirpacemakers programmed in the bipolar mode after six months. This study con firms earlier acute data that the bipolar pacing mode is superior to the unipolar mode for permanent pacemaker therapy.

Time Domain and Spectral Analysis of Electrograms in Man During Regular Ventricular Activity and Ventricular Fibrillation

Electrogram signals from intramyocardially placed wire electrodes were recorded in 24 open heart surgery patients during regular heart activity (RHA) and ventricular fibrillation (VF). Time domain parameters, maximal amplitudes (AMAX, UMAX), maximal derivatives (DMAX, SMAX), and power spectra in the frequency region up to 100 Hz were analyzed off-line on a digital computer. DMAX, AMAX, SMAX, and UMAX were significantly lower postoperatively than during the operation in RHA, median values reduced by 37, 23, 54, and 50 percent. Corresponding reductions in median values of 64, 39, 58, and 30 percent occurred in the transition from RHA to VF during the operation (peroperatively).

Ultrastructural studies on the growth of filaments and sarcomeres in mechanically overloaded human hearts

SummaryThe ultrastructure of myocardial cells was studied in four patients with left ventricular myocardial hypertrophy due to aortic and/or mitral valvular disease. Signs of cellular lysis and synthesis were present in juxtanuclear, interfibrillar, and subsarcolemmal areas. Subsarcolemmal areas contained a granular matrix with foci of polyribosomes, mitochondria, well preserved membranes, a proliferating sarcoplasmic reticulum, and thick and thin filaments and Z-band formations at different stages of development. Z-band substance and thin filaments appeared in the cytoplasm in close proximity to free polyribosomes and endoplasmic membranes and were seemingly not associated with the sarcolemma. These findings were interpreted as evidence for a proteosynthetic activity leading to the formation of new myofibrils and sarcomeres during the chronic stage of hypertrophy. Comparative studies showed that this process has much in common with the genesis of contractile cardiac units in the mammalian embryo. Anomalous Z-band accumulations were studied in normal myocardial cells of various vertebrates and in cells of the overloaded human heart. No evidence of a proteosynthetic activity was detected in the expanded Z-bands.

Primary 9 + 0 cilia in the embryonic and the adult human heart.

SummaryPrimary 9+0 cilia have been found in the embryonic and the adult human heart. Proximally the cilia show the typical (+0 filament arrangement. Rearrangement of the filaments occur in their distal regions. The cilia are usually found in deep invaginations of the cell membrane, but can also be found in a superficial position. Close connections are frequently found between cilia and thin cytoplasmic extensions from neighbouring cells.

Effects of isoproterenol on the dense core and perigranular membrane of atrial specific granules

SummaryFollowing subcutaneous injections of isoproterenol hydrochloride (ISO), atrial cells present a large number of partly degranulated or completely clear “specific granules” enclosed by an intact membrane. Such profiles were never encountered in normal controls and might suggest ISO-induced release of a secretory product. Permeability of perigranular membrane was tested using the extracellular macromolecular tracer horseradish peroxidase (HRP). Reaction product was entirely absent within granules of atrial cells in which the sarcolemma was made permeable to HRP molecules by the ISO injections. This seemed to be the case even in heavily labelled cells in which the peroxidase had penetrated the mitochondrial membranes. In atrial cells impermeable to the tracer, the specific granules closely apposed to the sarcolemma were always HRP-negative. The release mechanism of a possible secretory substance from the specific granules is discussed.

Continuous measurement of aortic blood velocity, after cardiac surgery, by means of an extractable doppler ultrasound probe

A new method has been developed for the continuous measurement of aortic blood velocity in patients following cardiac surgery. Using an extractable Doppler ultrasound probe placed on the ascending aorta, the changes in aortic velocity were recorded up to 24 h postoperatively, in 14 patients undergoing coronary bypass surgery. Volume flow rate is calculated from the mean velocity, the diameter of the aorta and the angle between the ultrasound beam and the direction of the blood flow, by means of an analogue flow calculator. Estimation of aortic flow showed a correlation of r = 0.79 with cardiac output measured by a thermodilution technique. The main advantage of the system is that it allows continuous monitoring of cardiac output, as well as short and long-term trend analyses, during the early postoperative period.

Electrophysiological properties of a new permanent endocardial lead for uni- and bipolar pacing.

BRElVIK, K., ENGEDAL, H., and OHM, O.‐J.; Ehctropbysiological properties of a new permanent endocardial lead for uni‐ and bipolar pacing. Unipolar and bipolar electrode systems were compared for electrogram amplitudes and slew rates, signal source impedance, and myocardial stimulation threshold and resistance in 15 consecutive patients who received a new endocardial electrode (Cordis 325–161). The bipolar electrograms showed the highest amplitude in nine of the patients (60%). The unipolar and bipolar electrograms were equal in four patients (26.7%), whereas the unipolar electrograms were highest in only two patients (13.3%). The difference in mean amplitude between bipolar (11.1 mV) and unipolar (10.1 mV) electrograms was statistically significant (p 0.05). Mean slew rates were almost equal (1.7 versus 1.6 V/s; p > 0.1). The bipolar electrode system always gave somewhat higher signal source impedance than the unipolar system (p 0.001). The current threshold was significantly lower during bipolar pacing (0.59 mA) in constant current pacing mode, than during unipolar pacing (0.65 mA) (p < 0.05). No significant differences were found during constant voltage pacing. Stimulation resistance was highest in the bipolar electrode system (p < 0.001). We conclude that the bipolar eiectrode system is as good as, or better than, the unipolar system both for ventricular sensing and for pacing. (PACE, Vol. 5, March‐April, 1982)

Ultrastructural studies on the formation of myofilaments and myofibrils in the human embryonic and adult hypertrophied heart

SummaryThe myofibrillogenesis in the human embryonic heart is described. The synthesis of thin filaments, which are the first to appear, takes place in close proximity to smooth surfaced SR tubules. Z-band material is closely related to the thin filaments and appears first as irregularly distributed patches in the filamenteous mass. Further cellular differentiation includes an organization of the thin filaments/Z-band material. The synthesis of thick filaments, which follows that of the thin filaments, takes place in ribosome rich areas of the cell. They are rapidly incorporated into the strings of organized thin filaments/Z-band material. The periodic binding sites on both kinds of filaments are believed to play an important role in the precise ordering of the filaments.The formation of myofilaments in the adult hypertrophied human heart is also described. The similarities between this process and that observed in the embryonic heart are striking, and we believe it to be the same process.

Ultrastructure of mitochondria-containing nuclei in human myocardial cells

SummaryThe ultrastructure of myocardial cell nuclei was examined in a group of 12 patients undergoing cardiopulmonary bypass surgery. In one patient (aged 60 years) with rheumatic heart disease, myocardial cells were observed which contained mitochondria with well preserved membranes within their nuclei. Such intranuclear mitochondria were observed with equal frequency in all of the three stages examined,i. e. at the start and end of aortic crossclamping and after 20 min of reperfusion.Approximately 2–3% of the total number of nuclei studied in this patient contained mitochondria. A partial disintegration of the membranes of the affected nuclei was sometimes seen. These findings are discussed in relation to the hypothesis of ade novo synthesis of mitochondria inside the nucleus, and, also, in relation to the “trapping theory” of mitochondria through the nuclear envelope.

Postoperative Doppler Echocardiographic Evaluation in Different Sizes of Medtronic-Hall, Biocor and Carpentier-Edwards S.A.V. Prosthetic Aortic Valves

Doppler echocardiography was performed on 108 patients 4-15 days after implantation of a Medtronic-Hall, Biocor or Carpentier-Edwards S.A.V. prosthetic aortic valve because of aortic stenosis. Significant correlation was found between the in vitro (maker-declared) and the Doppler-estimated effective prosthetic valve orifice area (r = 0.70, p < 0.01). Doppler-estimated prosthetic valve orifice area, but not transprosthetic blood velocities, discriminated between different sizes of Medtronic-Hall and Biocor valves. The effective orifice area in these valves was 57% of the in vitro area, but in Carpentier-Edwards valves it was only 43%. Transprosthetic blood velocity was inversely related to orifice area in men, but not in women, who also had longer duration of systole and better preservation of systolic left ventricular function. The data suggest that the effective prosthetic valve areas found in patients are significantly smaller than the experimental in vitro areas. Prosthesis size and type, anatomic and hemodynamic variables and gender are important in Doppler estimation of effective valve area.