Correspondence / American Journal of Emergency Medicine 32 (2014) 86–106
Recurrent central venous malposition caused by severe lower airway distortion
To the Editor, Correct placement of central venous catheter (CVC) should be confirmed radiologically before using it. It is always a challenge to place CVC at a right anatomical position. Malposition of CVC varies widely, ranging from less than 1% to more than 60% [1]. Cannulation by the right subclavian vein is associated with the highest risk of malposition of approximately 9.1%, most commonly in the ipsilateral internal jugular vein [2]. We had encountered a case where we failed to insert the catheter through the right internal jugular vein, and it went into ipsilateral internal jugular vein when cannulation tried by the right subclavian vein. All our measures to correct the malposition of CVC failed probably because of distortion by severe airway deformity. We wish to report such a malposition of CVC caused by severe tracheobronchial deformity after obtaining consent from the patient. A 56-year-old male patient who was a known smoker for the last 20 years presented in our emergency department with fever and shortness of breath. He also was diagnosed to have chronic obstructive pulmonary disease and chronic kidney disease (without any dialysis) since the last 10 years. His history revealed pulmonary tuberculosis 15 years back and received antitubercular therapy for 6 months. On examination, he was conscious but slightly tachypnic (respiratory rate, 25 breaths/min), with pulse oxymetry showing 96% on oxygen by venturi mask (40%). His blood pressure was 86/48 mm Hg on noninvasive measurement with heart rate of 120 beats/min, even after fluid resuscitation with 1 L of normal saline. Coagulation profile was within normal limits. We decided to put CVC through right internal jugular vein, but we failed to insert the guidewire beyond 10 cm only after 2 to 3 attempts with the help of ultrasound. Then we changed the approach through right subclavian vein, and we were able to insert the CVC. However, post-CVC radiology showed catheter in ipsilateral internal jugular vein. His chest x-ray also showed severe tracheobronchial deformity toward the right side, with changes suggestive of chronic bronchitis and old tuberculosis (Fig.). Then we tried to readjust the catheter with the help of guidewire toward the right atrium while occluding the right internal jugular vein manually at the same time. Again, we failed thrice, each time the catheter was going only toward the right internal jugular vein as confirmed by
101
ultrasonography. Then we abandoned the readjustment procedure. We maintain the subclavian catheter after withdrawing its tip up to the lower part of the internal jugular vein for use. Central venous catheter insertion is a common procedure used in monitoring central venous pressure (CVP), administration of vasoactive drugs, antineoplastic treatment, parenteral nutrition, and bone marrow transplantation. It is performed usually through internal jugular or subclavian veins. Central venous catheter tip is usually placed at the junction of SVC and the right atrium for accurate CVP measurement [3]. Catheter malpositioning is a known complication of central venous catheterization detected by immediate check chest xray or ultrasonography-guided placemen. Lumley and Russell [4] reported that neck compression is a useful test for diagnosing this complication because neck compression on the side of malposition will impede the flow in the vein. This will result in a rise of 10 cm H2O or more in CVP reading. Cannulation by the right subclavian vein was associated with the highest risk of malposition (9.1%), compared with 1.4% by the right internal jugular vein [2]. During subclavian vein catheterization, the most common misplacement of the catheter is cephalad, into the ipsilateral internal jugular vein (IJV), accounting for 60% to 70% of all malpositioning [5]. Other sites for malpositioning mentioned in the literature include the azygos vein, left superior intercostal vein, and thymic vein [6]. One study reported that manual occlusion of the ipsilateral IJV during subclavian vein cannulation reduced the chances of advancement of the CVC into the ipsilateral IJV. The frequency of malpositioning is related to the anatomical approach and catheter type used, but not to the physician's experience. Misplacements are more frequent with soft silicone catheters than with semirigid catheters [7]. Ultrasound is being used nowadays to guide insertion of CVC. Some authors suggest that ultrasound guidance improves the success rate of subclavian venous catheterization performed by less experienced operators [8]. On the other hand, other authors find that ultrasound guidance had no effect on the rate of complications or failures of subclavian vein catheterization [9]. Hence, insertion of CVC remains essentially a blind procedure that used guidance of fixed bony points. There is always a chance of malposition of the catheter. Some authors suggest excessive lengths of guidewire as the cause [10]. Other authors consider the length of the CVC inserted itself to be a risk factor. This may be also influenced by the initial orientations of the J-type guidewire tip as well as the guidewire course during the subclavian approach [11,12]. They said that keeping the J-tip of the guidewire directed caudad resulting in increased correct placement of CVC. Reinsertion of the catheters is also associated with potential complications and more ever the possibility of repeating the malposition. Recurrent malposition of CVC as in our case is attributed to severe trachea bronchial deformity compressing on superior vena cava and right brachiocephalic vein, leading the guidewire in ipsilateral IJV. This etiology of malposition of CVC has never been reported in the literature. The author suggests to rule out any possible factors for malposition of CVC (specially in recurrent) before insertion with exploring proper history, physical examination, and radiologic investigations. Sujay Samanta MD Department of Critical Care Medicine Sanjay Gandhi Post Graduate Institute of Medical Sciences Lucknow, India Sukhen Samanta MD Department of Anesthesia&Critical Care (Trauma Centre) JPNA Trauma Centre AIIMS, New Delhi, India E-mail address: [email protected]
Fig. Chest x-ray showing severe lower airway distortion leading to recurrent central venous malposition.
http://dx.doi.org/10.1016/j.ajem.2013.10.018
102
Correspondence / American Journal of Emergency Medicine 32 (2014) 86–106
References [1] Malatinsky J, Kadlic T, Majek M, Samel M. Misplacement and loop formation of central venous catheters. Acta Anaesthesiol Scand 1976;20: 237–47. [2] Pikwer A, Bååth L, Davidson B, Perstoft I, Akeson J. The incidence and risk of central venous catheter malpositioning: a prospective cohort study in 1619 patients. Anaesth Intensive Care 2008;36:30–7. [3] McGee WT, Ackerman BL, Rouben LR, et al. Accurate placement of central venous catheters: a prospective, randomized, multicenter trial. Crit Care Med 1993;21: 1118–23. [4] Lumley J, Russell WJ. Insertion of central venous catheters through arm veins. Anaesth Intensive Care 1975;3:101–4. [5] Ambesh SP, Pandey JC, Dubey PK. Internal jugular vein occlusion test for rapid diagnosis of misplaced subclavian vein catheter into the internal jugular vein. Anesthesiology 2001;95:1377–9. [6] Currarino G. Migration of jugular or subclavian venous catheters into inferior tributaries of the brachiocephalic veins or into the azygos vein, with possible complications. Pediatr Radiol 1996;26:439–49. [7] Muhm M, Sunder-Plassmann G, Apsner R, et al. Malposition of central venous catheters. Incidence, management and preventive practices. Wien Klin Wochenschr 1997;109:400–5. [8] Gualtieri E, Deppe SA, Sipperly ME, Thompson DR. Subclavian venous catheterization: greater success rate for less experienced operators using ultrasound guidance. Crit Care Med 1995;23:692–7. [9] Mansfield PF, Hohn DC, Fornage BD, Gregurich MA, Ota DM. Complications and failures of subclavian-vein catheterization. N Engl J Med 1994;29: 1735–8. [10] Andrews RT, Bova DA, Venbrux AC. How much guidewire is too much? Direct measurement of the distance from subclavian and internal jugular vein access sites to the superior vena cava-atrial junction during central venous catheter placement. Crit Care Med 2000;28:138–42. [11] Hwang JW, Han SH, Bahk JH, Oh YS. Influence of orientations of guide wire tip on the placement of subclavian venous catheters. Acta Anaesthesiol Scand 2005;49: 14603. [12] Tripathi M, Dubey PK, Ambesh SP. Direction of the J-tip of the guidewire, in Seldinger technique, is a significant factor in misplacement of subclavian vein catheter: a randomized, controlled study. Anesth Analg 2005;100:21–4.
Voltage attenuation of the electrocardiogram in Takotsubo syndrome: what ED physicians should consider☆ To the Editor, The case report by Bashir et al, published online ahead of print on October 3, 2013, in British Medical Journal Case Reports [1], exemplifies the electrocardiogram (ECG), with which emergency department (ED) physicians have to grapple with, when confronted with patients who may have either an underlying acute coronary syndrome (ACS) or Takotsubo syndrome (TTS). The authors describe a woman in her mid 80s who presented with TTS and showed in her admission ECG “anterolateral ST-segment elevation with loss of R waves, consistent with an acute myocardial infarction.” The patient had a complete recovery and at follow-up at 3 months later showed “evidence of recovery of anterior R waves on ECG.” Indeed there was a reappearance of the R-waves in the precordial leads V1-V3 in the follow-up ECG [1], although not infrequently the “R-wave regeneration” in serial ECGs is due to the common problem of variation in the placement of the precordial lead electrodes on the chest wall. The authors did not comment on the persistent T-wave inversions in the follow-up ECG, which along with QTc prolongation are common ECG features of TTS, evident during many weeks or months of the recovery phase of TTS [2]. But what is striking at a glance in the comparison of the 2 ECGs is the voltage attenuation (VATT) of the QRS complexes of all 12 leads in the admission ECG, an insight reported
☆ Conflicts of Interest Disclosure: There is nothing to disclose.
recently [3-5], which is relevant to the ED physicians, in the differential diagnosis of ACS and TTS, which has obviously management connotations (cardiac catheterization and percutaneous coronary interventions for patients with ACS and supportive care for patients with TTS). In the time-urgent setting of ED, the admission ECG of a patient suspected of having possible TTS is the most crucial piece of information which needs to be exploited to its full. What is practiced currently leaves a lot to be desired. A winning relevant scenario could easily be adopted and implemented and could evolve along the following steps: (1) Along with starting the sequence of ECG recordings, serial sampling for cardiac biomarkers, instituting ECG monitoring, and contacting cardiology, the ED physician should inspect the ECG for ST-segment elevations or depressions, T-wave inversions, prolongation of the QTc, and VATT of the QRS complexes in some or all 12 ECG leads; (2) the hospital ECG file of the patient should be accessed immediately for a possible previous ECG, and in such a case, a comparison with the admission ECG should be made regarding VATT of the QRS complexes in the admission ECG; (3) information should be sought from the patient or his/her relatives whether a previous ECG has been obtained at another facility, and a concerted effort should be made to have such ECG faxed, or transmitted otherwise electronically, to the ED, immediately; (4) a facilitation of this proposed “modus operandi” has already been happening, and it is based o the use of the ubiquitous “smart” phones, tablets, “cloud computing” (storage of vast amounts of information in Internet electronic platforms, available for access to authorized individuals) [6] of ECG data, and “smart health cards” (electronic cards, already implemented in certain countries, containing the entirety of health related information of a particular individual, including images from various diagnostic tests, and ECGs) [7], enabling physicians to access patients’ previous ECGs, regardless of where geographically have been recorded. It is conceivable that putting the above ideas to action may facilitate the triage of patients to appropriate care, possibly obviate unnecessary invasive procedures (urgent coronary arteriography in patients subsequently diagnosed as having suffered TTS), and save many lives. John E. Madias MD Icahn School of Medicine at Mount Sinai New York NY, USA Division of Cardiology, Elmhurst Hospital Center Elmhurst NY 11373, USA E-mail address: [email protected] http://dx.doi.org/10.1016/j.ajem.2013.10.023 References [1] Bashir A, Noroozian N, Steeds RP, Khan SQ. Imaging features in takotsubo cardiomyopathy. BMJ Case Rep. 2013 Oct 3;2013(oct03_1). pii: bcr2013201394. http://dx.doi.org/10.1136/bcr-2013-201394. [2] Madias JE. Electrocardiogram in myocardial edema due to Takotsubo syndrome. J Electrocardiol 2012;45:795–6. [3] Madias JE. Transient attenuation of the amplitude of the QRS complexes in the diagnosis of Takotsubo syndrome. Eur Heart J: acute cardiovascular care (in press). [4] Madias JE. Electrocardiogram lead-specific QRS attenuation in an atypical midventricular case of Takotsubo syndrome. J Electrocardiol. 2013 Sep 9. pii: S0022-0736(13)00414-7. http://dx.doi.org/10.1016/j.jelectrocard.2013.08.008. [Epub ahead of print]. [5] Madias JE. Electrocardiogram repolarization changes in patients with Takotsubo and acute coronary syndromes. American Journal of Cardiology (in press). [6] Bond RR, Finlay DD, Nugent CD, Moore G, Guldenring D. Methods for presenting and visualising electrocardiographic data: from temporal signals to spatial imaging. J Electrocardiol 2013;46:182–96. [7] http://www.ihealthbeat.org/articles/2011/6/16/medical-smart-cards-could-boostportability-of-patient-health-data.aspx (last accessed 10/5/13).
Recurrent central venous malposition caused by severe lower airway distortion
To the Editor, Correct placement of central venous catheter (CVC) should be confirmed radiologically before using it. It is always a challenge to place CVC at a right anatomical position. Malposition of CVC varies widely, ranging from less than 1% to more than 60% [1]. Cannulation by the right subclavian vein is associated with the highest risk of malposition of approximately 9.1%, most commonly in the ipsilateral internal jugular vein [2]. We had encountered a case where we failed to insert the catheter through the right internal jugular vein, and it went into ipsilateral internal jugular vein when cannulation tried by the right subclavian vein. All our measures to correct the malposition of CVC failed probably because of distortion by severe airway deformity. We wish to report such a malposition of CVC caused by severe tracheobronchial deformity after obtaining consent from the patient. A 56-year-old male patient who was a known smoker for the last 20 years presented in our emergency department with fever and shortness of breath. He also was diagnosed to have chronic obstructive pulmonary disease and chronic kidney disease (without any dialysis) since the last 10 years. His history revealed pulmonary tuberculosis 15 years back and received antitubercular therapy for 6 months. On examination, he was conscious but slightly tachypnic (respiratory rate, 25 breaths/min), with pulse oxymetry showing 96% on oxygen by venturi mask (40%). His blood pressure was 86/48 mm Hg on noninvasive measurement with heart rate of 120 beats/min, even after fluid resuscitation with 1 L of normal saline. Coagulation profile was within normal limits. We decided to put CVC through right internal jugular vein, but we failed to insert the guidewire beyond 10 cm only after 2 to 3 attempts with the help of ultrasound. Then we changed the approach through right subclavian vein, and we were able to insert the CVC. However, post-CVC radiology showed catheter in ipsilateral internal jugular vein. His chest x-ray also showed severe tracheobronchial deformity toward the right side, with changes suggestive of chronic bronchitis and old tuberculosis (Fig.). Then we tried to readjust the catheter with the help of guidewire toward the right atrium while occluding the right internal jugular vein manually at the same time. Again, we failed thrice, each time the catheter was going only toward the right internal jugular vein as confirmed by
101
ultrasonography. Then we abandoned the readjustment procedure. We maintain the subclavian catheter after withdrawing its tip up to the lower part of the internal jugular vein for use. Central venous catheter insertion is a common procedure used in monitoring central venous pressure (CVP), administration of vasoactive drugs, antineoplastic treatment, parenteral nutrition, and bone marrow transplantation. It is performed usually through internal jugular or subclavian veins. Central venous catheter tip is usually placed at the junction of SVC and the right atrium for accurate CVP measurement [3]. Catheter malpositioning is a known complication of central venous catheterization detected by immediate check chest xray or ultrasonography-guided placemen. Lumley and Russell [4] reported that neck compression is a useful test for diagnosing this complication because neck compression on the side of malposition will impede the flow in the vein. This will result in a rise of 10 cm H2O or more in CVP reading. Cannulation by the right subclavian vein was associated with the highest risk of malposition (9.1%), compared with 1.4% by the right internal jugular vein [2]. During subclavian vein catheterization, the most common misplacement of the catheter is cephalad, into the ipsilateral internal jugular vein (IJV), accounting for 60% to 70% of all malpositioning [5]. Other sites for malpositioning mentioned in the literature include the azygos vein, left superior intercostal vein, and thymic vein [6]. One study reported that manual occlusion of the ipsilateral IJV during subclavian vein cannulation reduced the chances of advancement of the CVC into the ipsilateral IJV. The frequency of malpositioning is related to the anatomical approach and catheter type used, but not to the physician's experience. Misplacements are more frequent with soft silicone catheters than with semirigid catheters [7]. Ultrasound is being used nowadays to guide insertion of CVC. Some authors suggest that ultrasound guidance improves the success rate of subclavian venous catheterization performed by less experienced operators [8]. On the other hand, other authors find that ultrasound guidance had no effect on the rate of complications or failures of subclavian vein catheterization [9]. Hence, insertion of CVC remains essentially a blind procedure that used guidance of fixed bony points. There is always a chance of malposition of the catheter. Some authors suggest excessive lengths of guidewire as the cause [10]. Other authors consider the length of the CVC inserted itself to be a risk factor. This may be also influenced by the initial orientations of the J-type guidewire tip as well as the guidewire course during the subclavian approach [11,12]. They said that keeping the J-tip of the guidewire directed caudad resulting in increased correct placement of CVC. Reinsertion of the catheters is also associated with potential complications and more ever the possibility of repeating the malposition. Recurrent malposition of CVC as in our case is attributed to severe trachea bronchial deformity compressing on superior vena cava and right brachiocephalic vein, leading the guidewire in ipsilateral IJV. This etiology of malposition of CVC has never been reported in the literature. The author suggests to rule out any possible factors for malposition of CVC (specially in recurrent) before insertion with exploring proper history, physical examination, and radiologic investigations. Sujay Samanta MD Department of Critical Care Medicine Sanjay Gandhi Post Graduate Institute of Medical Sciences Lucknow, India Sukhen Samanta MD Department of Anesthesia&Critical Care (Trauma Centre) JPNA Trauma Centre AIIMS, New Delhi, India E-mail address: [email protected]
Fig. Chest x-ray showing severe lower airway distortion leading to recurrent central venous malposition.
http://dx.doi.org/10.1016/j.ajem.2013.10.018
102
Correspondence / American Journal of Emergency Medicine 32 (2014) 86–106
References [1] Malatinsky J, Kadlic T, Majek M, Samel M. Misplacement and loop formation of central venous catheters. Acta Anaesthesiol Scand 1976;20: 237–47. [2] Pikwer A, Bååth L, Davidson B, Perstoft I, Akeson J. The incidence and risk of central venous catheter malpositioning: a prospective cohort study in 1619 patients. Anaesth Intensive Care 2008;36:30–7. [3] McGee WT, Ackerman BL, Rouben LR, et al. Accurate placement of central venous catheters: a prospective, randomized, multicenter trial. Crit Care Med 1993;21: 1118–23. [4] Lumley J, Russell WJ. Insertion of central venous catheters through arm veins. Anaesth Intensive Care 1975;3:101–4. [5] Ambesh SP, Pandey JC, Dubey PK. Internal jugular vein occlusion test for rapid diagnosis of misplaced subclavian vein catheter into the internal jugular vein. Anesthesiology 2001;95:1377–9. [6] Currarino G. Migration of jugular or subclavian venous catheters into inferior tributaries of the brachiocephalic veins or into the azygos vein, with possible complications. Pediatr Radiol 1996;26:439–49. [7] Muhm M, Sunder-Plassmann G, Apsner R, et al. Malposition of central venous catheters. Incidence, management and preventive practices. Wien Klin Wochenschr 1997;109:400–5. [8] Gualtieri E, Deppe SA, Sipperly ME, Thompson DR. Subclavian venous catheterization: greater success rate for less experienced operators using ultrasound guidance. Crit Care Med 1995;23:692–7. [9] Mansfield PF, Hohn DC, Fornage BD, Gregurich MA, Ota DM. Complications and failures of subclavian-vein catheterization. N Engl J Med 1994;29: 1735–8. [10] Andrews RT, Bova DA, Venbrux AC. How much guidewire is too much? Direct measurement of the distance from subclavian and internal jugular vein access sites to the superior vena cava-atrial junction during central venous catheter placement. Crit Care Med 2000;28:138–42. [11] Hwang JW, Han SH, Bahk JH, Oh YS. Influence of orientations of guide wire tip on the placement of subclavian venous catheters. Acta Anaesthesiol Scand 2005;49: 14603. [12] Tripathi M, Dubey PK, Ambesh SP. Direction of the J-tip of the guidewire, in Seldinger technique, is a significant factor in misplacement of subclavian vein catheter: a randomized, controlled study. Anesth Analg 2005;100:21–4.
Voltage attenuation of the electrocardiogram in Takotsubo syndrome: what ED physicians should consider☆ To the Editor, The case report by Bashir et al, published online ahead of print on October 3, 2013, in British Medical Journal Case Reports [1], exemplifies the electrocardiogram (ECG), with which emergency department (ED) physicians have to grapple with, when confronted with patients who may have either an underlying acute coronary syndrome (ACS) or Takotsubo syndrome (TTS). The authors describe a woman in her mid 80s who presented with TTS and showed in her admission ECG “anterolateral ST-segment elevation with loss of R waves, consistent with an acute myocardial infarction.” The patient had a complete recovery and at follow-up at 3 months later showed “evidence of recovery of anterior R waves on ECG.” Indeed there was a reappearance of the R-waves in the precordial leads V1-V3 in the follow-up ECG [1], although not infrequently the “R-wave regeneration” in serial ECGs is due to the common problem of variation in the placement of the precordial lead electrodes on the chest wall. The authors did not comment on the persistent T-wave inversions in the follow-up ECG, which along with QTc prolongation are common ECG features of TTS, evident during many weeks or months of the recovery phase of TTS [2]. But what is striking at a glance in the comparison of the 2 ECGs is the voltage attenuation (VATT) of the QRS complexes of all 12 leads in the admission ECG, an insight reported
☆ Conflicts of Interest Disclosure: There is nothing to disclose.
recently [3-5], which is relevant to the ED physicians, in the differential diagnosis of ACS and TTS, which has obviously management connotations (cardiac catheterization and percutaneous coronary interventions for patients with ACS and supportive care for patients with TTS). In the time-urgent setting of ED, the admission ECG of a patient suspected of having possible TTS is the most crucial piece of information which needs to be exploited to its full. What is practiced currently leaves a lot to be desired. A winning relevant scenario could easily be adopted and implemented and could evolve along the following steps: (1) Along with starting the sequence of ECG recordings, serial sampling for cardiac biomarkers, instituting ECG monitoring, and contacting cardiology, the ED physician should inspect the ECG for ST-segment elevations or depressions, T-wave inversions, prolongation of the QTc, and VATT of the QRS complexes in some or all 12 ECG leads; (2) the hospital ECG file of the patient should be accessed immediately for a possible previous ECG, and in such a case, a comparison with the admission ECG should be made regarding VATT of the QRS complexes in the admission ECG; (3) information should be sought from the patient or his/her relatives whether a previous ECG has been obtained at another facility, and a concerted effort should be made to have such ECG faxed, or transmitted otherwise electronically, to the ED, immediately; (4) a facilitation of this proposed “modus operandi” has already been happening, and it is based o the use of the ubiquitous “smart” phones, tablets, “cloud computing” (storage of vast amounts of information in Internet electronic platforms, available for access to authorized individuals) [6] of ECG data, and “smart health cards” (electronic cards, already implemented in certain countries, containing the entirety of health related information of a particular individual, including images from various diagnostic tests, and ECGs) [7], enabling physicians to access patients’ previous ECGs, regardless of where geographically have been recorded. It is conceivable that putting the above ideas to action may facilitate the triage of patients to appropriate care, possibly obviate unnecessary invasive procedures (urgent coronary arteriography in patients subsequently diagnosed as having suffered TTS), and save many lives. John E. Madias MD Icahn School of Medicine at Mount Sinai New York NY, USA Division of Cardiology, Elmhurst Hospital Center Elmhurst NY 11373, USA E-mail address: [email protected] http://dx.doi.org/10.1016/j.ajem.2013.10.023 References [1] Bashir A, Noroozian N, Steeds RP, Khan SQ. Imaging features in takotsubo cardiomyopathy. BMJ Case Rep. 2013 Oct 3;2013(oct03_1). pii: bcr2013201394. http://dx.doi.org/10.1136/bcr-2013-201394. [2] Madias JE. Electrocardiogram in myocardial edema due to Takotsubo syndrome. J Electrocardiol 2012;45:795–6. [3] Madias JE. Transient attenuation of the amplitude of the QRS complexes in the diagnosis of Takotsubo syndrome. Eur Heart J: acute cardiovascular care (in press). [4] Madias JE. Electrocardiogram lead-specific QRS attenuation in an atypical midventricular case of Takotsubo syndrome. J Electrocardiol. 2013 Sep 9. pii: S0022-0736(13)00414-7. http://dx.doi.org/10.1016/j.jelectrocard.2013.08.008. [Epub ahead of print]. [5] Madias JE. Electrocardiogram repolarization changes in patients with Takotsubo and acute coronary syndromes. American Journal of Cardiology (in press). [6] Bond RR, Finlay DD, Nugent CD, Moore G, Guldenring D. Methods for presenting and visualising electrocardiographic data: from temporal signals to spatial imaging. J Electrocardiol 2013;46:182–96. [7] http://www.ihealthbeat.org/articles/2011/6/16/medical-smart-cards-could-boostportability-of-patient-health-data.aspx (last accessed 10/5/13).
