Technological and Clinical Challenges in Lead Placement for Cardiac Rhythm Management Devices.

Cardiac disease is a leading cause of death worldwide. Disturbance in the conduction system of the heart may trigger or aggravate heart dysfunction, affecting the efficiency of the heart, and lead to heart failure or cardiac arrest. Patients may require implantable cardiac rhythm management devices (ICRMDs) to maintain or restore the heart rhythm. ICRMDs have undergone important improvements, yet limitations still exist, presenting important technological challenges. Most ICRMDs consist of a subcutaneous control unit and intracardiac electrodes. The leads, which connect the electrodes to the control unit, are usually placed transvenously through the subclavian veins. Various locations inside the heart are used for placement of electrodes, depending on the specific condition. Some of the limitations to effective pacemaker therapy are associated with placement and location of the leads. Various approaches have been developed to overcome these challenges, such as multi-site pacing and leadless solutions. This paper aims to review the state of the art for the selection of placement sites for pacemakers, implantable cardioverter defibrillator (ICD) and cardiac resynchronization therapy devices (CRT) devices and discuss potential technological advancements to improve the results of ICRMD-therapy including development av leadless technology.

Myocardial tissue CO2 tension detects coronary blood flow reduction after coronary artery bypass in real-time†.

BACKGROUND: Coronary stenosis after coronary artery bypass grafting (CABG) may lead to myocardial ischaemia and is clinically difficult to diagnose. In a CABG model, we aimed at defining variables that detect hypoperfusion in real-time and correlate with impaired regional ventricular function by monitoring myocardial tissue metabolism. METHODS: Off-pump CABG was performed in 10 pigs. Graft blood flow was reduced in 18 min intervals to 75, 50, and 25% of baseline flow with reperfusion between each flow reduction. Myocardial tissue Pco2 (Pt(CO2)), Po2, pH, glucose, lactate, and glycerol from the graft supplied region and a control region were obtained. Regional cardiac function was assessed as radial strain. RESULTS: In comparison with baseline, myocardial pH decreased during 75, 50, and 25% flow reduction (-0.15; -0.22; -0.37, respectively, all P<0.05) whereas Pt(CO2) increased (+4.6 kPa; +7.8 kPa; +12.9 kPa, respectively, all P<0.05). pH and Pt(CO2) returned to baseline upon reperfusion. Lactate and glycerol increased flow-dependently, while glucose decreased. Regional ventricular contractile function declined significantly. All measured variables remained normal in the control region. Pt(CO2) correlated strongly with tissue lactate, pH, and contractile function (R=0.86, R=-0.91, R=-0.70, respectively, all P<0.001). New conductometric Pt(CO2) sensors were in agreement with established fibre-optic probes. Cardiac output was not altered. CONCLUSIONS: Myocardial pH and Pt(CO2) monitoring can quantify the degree of regional tissue hypoperfusion in real-time and correlated well with cellular metabolism and contractile function, whereas cardiac output did not. New robust conductometric Pt(CO2) sensors have the potential to serve as a clinical cardiac monitoring tool during surgery and postoperatively.

Diffuse reflectance spectroscopy: Systemic and microvascular oxygen saturation is linearly correlated and hypoxia leads to increased spatial heterogeneity of microvascular saturation.

The microvascular oxygen saturation (SmvO(2)) in the skin and tongue (sublingual mucosa) in pigs (n=6) was characterised using diffuse reflectance spectroscopy (DRS). The correlation between arterial oxygen saturation (SaO(2)) and SmvO(2) as well as the spatial heterogeneity of SmvO(2) was examined during hypoxia. DRS uses shallow-penetrating visible light to assess microvascular oxygen saturation (SmvO(2)) in superficial tissue. Hypoxia was induced by gradual reduction in ventilation or reduction of the inspiratory oxygen fraction. The spatial heterogeneity of SmvO(2) was expressed as the coefficient of variation (CV) of repeated SmvO(2) measurements. Baseline SmvO(2) before interventions was 20.2% (10.3%-38.1%, median with range) in groin skin, 32.9% (13.0%-49.3%) in the ear and 42.2% (32.1%-51.5%) in the tongue. SmvO(2) in the groin was significantly lower than venous oxygen saturation (SvO(2)) (p<0.05) and SmvO(2) in the tongue (p=0.03). There was a significant linear correlation between SaO(2) and SmvO(2) in all measuring sites for both interventions (p<0.05). Similarly there was a significant correlation between CV of repeated SmvO(2) measurements and SmvO(2) in all measuring sites for both interventions (p<0.01). The results from baseline measurements indicate a surprisingly high oxygen extraction in the measurement volume of DRS, especially in the groin skin. A reduction of SmvO(2) with decreasing SaO(2) was found and additionally the results suggest that spatial heterogeneity of microvascular oxygen saturation increases during hypoxia. Microvascular disturbances have been demonstrated in both local vascular diseases and systemic conditions such as shock and sepsis, an assessment of microvascular oxygen saturation using DRS may be useful in the monitoring of the microcirculation in such patients. This study is a part of an ongoing characterization of the DRS technique.

Assessments of skin and tongue microcirculation reveals major changes in porcine sepsis.

AIM: To examine the relation between central hemodynamics, clinical severity and microvascular findings in tongue and skin during sepsis. MATERIALS AND METHODS: Skin and tongue microcirculation was examined using laser Doppler and video microscopy techniques before and 200 min after inducing sepsis in pigs (n=6) by inactivated Neisseria meningitides and in two control animals. RESULTS: All infected pigs developed clinical signs of sepsis. Pericapillary bleedings developed in the tongue in the two pigs with the most severe disease. Capillary density increased in the groin skin in infected pigs after 200 min as compared to baseline (P<0·02). In the same period, mean capillary flow velocity was reduced in groin skin and tongue in septic pigs (P<0·02). At 200 min a fraction of capillaries had developed 'no flow' or 'brisk flow', patterns hardly seen at baseline. Laser Doppler perfusion was reduced in ear and tongue after 200 min (P<0·02 for both). The described pathology was more pronounced in the pigs with the most severe sepsis. CONCLUSION: Capillary bleedings may be used as an early indication of severe sepsis. Examination of skin and tongue microcirculations may be used to characterize severity of sepsis and possibly to assess effect of treatment.

Detection of myocardial ischaemia by epicardial accelerometers in the pig.

BACKGROUND: We describe a novel technique for continuous real-time assessment of myocardial ischaemia using a three-axis accelerometer. METHODS: In 14 anaesthetized open-chest pigs, two accelerometers were sutured on the left ventricle (LV) surface in the perfusion areas of the left anterior descending (LAD) and circumflex (CX) arteries. Acceleration was measured in the longitudinal, circumferential, and radial directions, and the corresponding epicardial velocities were calculated. Regional LV dysfunction was induced by LAD occlusion for 60 s. Global LV function was altered by nitroprusside, epinephrine, esmolol, and fluid loading. Epicardial velocities were compared with strain by echocardiography during LAD occlusion and with aortic flow and LV dP/dt(max) during interventions on global LV function. RESULTS: LAD occlusion induced ischaemia, shown by lengthening in systolic strain in the LV apical anterior region (P<0.01) and concurrent changes in LAD accelerometer circumferential velocities during systole (P<0.01) and during the isovolumic relaxation phase (P<0.01). The changes in accelerometer circumferential velocities during LAD occlusion were greater compared with the changes during the interventions on global function (P<0.01). For the LAD accelerometer circumferential velocities, sensitivity was 94-100% and specificity was 92-94% in detecting ischaemia. CONCLUSIONS: Myocardial ischaemia can be detected with epicardial three-axis accelerometers. The accelerometer had the ability to distinguish ischaemia from interventions altering global myocardial function. This novel technique may be used for continuous real-time monitoring of myocardial ischaemia during and after cardiac surgery.

Continuous cardiac output during off-pump coronary artery bypass surgery: pulse-contour analyses vs pulmonary artery thermodilution.

BACKGROUND: No gold standard method exists for monitoring continuous cardiac output (CO). In this study, the agreement between the two most frequently used methods, PiCCO pulse-contour analysis (PCCO) and STAT pulmonary artery thermodilution (STAT-CO), was assessed during multiple-vessel off-pump coronary artery bypass (OPCAB) surgery. METHODS: Thirty patients were enrolled in the study. Two time periods were defined during surgery; Period 1 included positioning of the heart and stabilizer device and Period 2 included the coronary occlusion. Measurements were obtained every minute during both periods. The agreement for the continuous CO and the change in CO (DeltaCO) was estimated using the Bland-Altman method. RESULTS: Significant changes in mean arterial pressure (DeltaMAP), central venous saturation, PCCO and STAT-CO were seen only during Period 1. DeltaMAP correlated only with changes in PCCO, (P < 0.001, r = 0.60). The mean difference (2sd) between PCCO and STAT-CO ranged from - 0.29 (1.82) to - 0.71 (2.57) litre min(-1), and the percentage error varied from 32 to 50%. For the CO measurements, the limits of agreements did not differ between Period 1 and Period 2. In contrast, for the DeltaCO measurements, the limits of agreements were wider in Period 1 than in the more haemodynamically stable Period 2. CONCLUSIONS: CCO and STAT-CO show large discrepancies in CO during OPCAB surgery. Clinically acceptable agreement was seen only for trends in CO during haemodynamically stable periods.

Agreement between PiCCO pulse-contour analysis, pulmonal artery thermodilution and transthoracic thermodilution during off-pump coronary artery by-pass surgery.

BACKGROUND: Haemodynamic instability during off-pump coronary artery bypass surgery (OPCAB) may appear rapidly, and continuous monitoring of the cardiac index (CI) during the procedure is advisable. With the PiCCO monitor, CI can be measured continuously and almost real time with pulse-contour analysis and intermittently with transthoracic thermodilution. The agreement between pulmonal artery thermodilution CI (Tpa), transthoracic thermodilution CI (Tpc) and pulse-contour CI (PCCI) during OPCAB surgery has not been evaluated sufficiently. METHODS: In 30 patients scheduled for OPCAB surgery, a pulmonary artery catheter and a PiCCO catheter were inserted. At different time points during surgery, Tpa, Tpc and PCCI were compared. Measurements were performed after induction of anesthesia (T1), after pericardiothomy (T2), after grafting on the anterior (T3), posterior (T4) and lateral (T5) walls and after chest closure (T6). The PCCI was recalibrated at time point T2-T6. RESULTS: Mean difference and the limits of agreements (percentage error) between Tpa and Tpc were: -0.14 +/- 0.60 (22.0%) l/min/m2, between Tpa and PCCI: -0.07 +/- 0.92 (33.5%) l/min/m2 and between Tpc and PCCI: 0.10 +/- 1.00 (35.5%) l/min/m2. For changes in CI from one time point to the next (DeltaCI), the limits of agreements between DeltaCI Tpa and DeltaCI Tpc were 0.04 +/- 0.90 l/min/m2, between DeltaCI Tpa and DeltaCI PCCI: -0.02 +/- 1.22 l/min/m2 and between DeltaCI Tpc and DeltaCI PCCI: -0.08 +/- 1.32 l/min/m2. CONCLUSION: In OPCAB surgery, limits of agreement comparing thermodilution methods were smaller than comparing PCCI with thermodilution. Recalibration of PCCI is therefore advisable.

[Occupational health care, coordination with primary health care]. / Bedriftshelsetjenesten, samordning med kommunehelsetjenesten.

Occupational health care is a privately financed health service offered to the healthiest part of the population. It is not governed in the same way as primary health care. In this paper we conclude that the present model of organization is inadequate. The entire responsibility for organization of occupational health care should be placed with the Ministry of Health and Social Affairs. This will ensure efficient use of resources.