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M Cooklin

Publications and source records attributed to M Cooklin.

14 recordsLinked to original sources
PubMed2005

Real-time three-dimensional echocardiography: a novel technique to quantify global left ventricular mechanical dyssynchrony.

BACKGROUND: Left ventricular (LV) mechanical dyssynchrony (LVMD) has emerged as a therapeutic target using cardiac resynchronization therapy (CRT) in selected patients with chronic heart failure. Current methods used to evaluate LVMD are technically difficult and do not assess LVMD of the whole LV simultaneously. We developed and validated real-time 3D echocardiography (RT3DE) as a novel method to assess global LVMD. METHODS AND RESULTS: Eighty-nine healthy volunteers and 174 unselected patients referred for routine echocardiography underwent 2D echocardiography and RT3DE. RT3DE data sets provided time-volume analysis for global and segmental LV volumes. A systolic dyssynchrony index (SDI) was derived from the dispersion of time to minimum regional volume for all 16 LV segments. Healthy subjects and patients with normal LV systolic function had highly synchronized segmental function (SDI, 3.5+/-1.8% and 4.5+/-2.4%; P=0.7). SDI increased with worsening LV systolic function regardless of QRS duration (mild, 5.4+/-0.83%; moderate, 10.0+/-2%; severe LV dysfunction, 15.6+/-1%; P for trend <0.001). We found that 37% of patients with moderate to severe LV systolic dysfunction had significant dyssynchrony with normal QRS durations (SDI, 14.7+/-1.2%). Twenty-six patients underwent CRT. At long-term follow-up, responders demonstrated reverse remodeling after CRT with a significant reduction in SDI (16.9+/-1.1% to 6.9+/-1%; P<0.0001) and end-diastolic volume (196.6+/-17.3 to 132.1+/-13.5 mL; P<0.0001) associated with an increase in LV ejection fraction (17+/-2.2% to 31.6+/-2.9%; P<0.0001). CONCLUSIONS: RT3DE can quantify global LVMD in patients with and without QRS prolongation. RT3DE represents a novel technique to identify chronic heart failure patients who may otherwise not be considered for CRT.

Computer Systems↗
PubMed2001

The action of isoprenaline on the electrophysiological properties of hypertrophied left ventricular myocytes.

The electrophysiological effects of the beta-agonist, isoprenaline, on hypertrophied left ventricular myocardium were measured to understand better the arrhythmic effects of beta-stimulation on the hypertrophied heart. Left ventricular hypertrophy was induced in guinea-pigs by constriction of the thoracic aorta. An age-matched sham-operated group served as controls. Isolated myocytes were held under voltage- and current clamp and the effect of isoprenaline on the L-type Ca2+ current, I(Ca), a Cl- current, I(Cl), and action potential morphology were measured. Cardiac growth was mirrored by cellular hypertrophy. I(Ca) and I(Cl) current density were reduced as myocyte hypertrophy progressed. The augmentation of I(Ca) and I(Cl) by isoprenaline was also reduced in hypertrophy, but no other characteristics of the two currents, or the dose-dependency of the action of isoprenaline were a function of cardiac growth. Isoprenaline prolonged the action potential, but to a smaller extent in hypertrophied myocytes. This difference in action potential prolongation was abolished by glibenclamide. The changes to I(Ca) and I(Cl) in hypertrophy would not tend to increase triggered activity in this situation. Under maximum inotropic stimulation hypertrophied myocytes show action potential changes which are consistent with intracellular ATP depletion, and which could enhance the likelihood of re-entrant circuits. A simple diffusion model for oxygen is constructed to demonstrate the possibility of cellular hypoxia in hypertrophied myocytes.

Action Potentials↗
PubMed2000

Clinical trials update: IMPROVEMENT-HF, COPERNICUS, MUSTIC, ASPECT-II, APRICOT and HEART.

Important new studies relevant to the field of heart failure reported at the annual congress of the European Society of Cardiology (ESC), held in Amsterdam in August 2000, are reviewed. The IMPROVEMENT of Heart Failure survey investigated the knowledge and perceptions of over 1300 primary care physicians from 14 ESC member nations and the actual practice in over 11000 of their patients. Guidelines and clinical practice were compared. The survey suggested, in this large sample, that the quality of care was higher than previous smaller surveys have suggested but have also identified important deficiencies in knowledge and management that should be rectified. The COPERNICUS study demonstrated that carvedilol was remarkably well tolerated even in patients with very severe heart failure and that treatment was associated with a substantial reduction in mortality even among patients that would conventionally not be considered, by many, for beta-blocker therapy. The MUSTIC trial suggested that cardiac resynchronisation using biventricular pacing improved patients symptomatically whether or not the patient was in atrial fibrillation. Morbidity and mortality studies of cardiac resynchronisation are now underway. The ASPECT-II and APRICOT-II studies investigated the role of warfarin, aspirin and their combination for the long-term management of myocardial infarction. One interpretation of the data from these studies is that the combination of aspirin and warfarin is about as effective as warfarin alone but with a much higher incidence of side effects. Warfarin alone appeared superior to aspirin alone. In summary, the annual congress of the ESC provided important new information for clinical practice and, to date, was, by far, the most important cardiology congress in the world this year.

Adrenergic beta-Antagonists↗
PubMed1999

Comparison of bipolar and integrated sensing for redetection of ventricular fibrillation.

BACKGROUND: Implantable cardioverter-defibrillator function is critically dependent on reliable sensing of intracardiac signals. Lead systems that use integrated sensing, in which the distal shocking coil is part of both the sensing and shocking pathways, may be prone to undersensing of ventricular fibrillation, especially during redetection after a failed first shock. To assess the effect of endocardial lead system on redetection, we compared a dedicated rate-sensing lead and 2 generations of integrated sensing defibrillator leads with a uniform testing algorithm and pulse generator. METHODS: The study group consisted of 72 patients after implantable cardioverter-defibrillator implantation. Three transvenous rate-sensing leads were evaluated: a standard pacing lead, incorporating true bipolar sensing without ventricular coils, or an integrated shocking and sensing lead (Endotak C) with either 6-mm (60 series) or 12-mm (70 series) spacing between the sensing tip and shocking coil. Redetection was assessed from a failed first shock just below defibrillation threshold. RESULTS: Compared with the dedicated bipolar lead, redetection was prolonged with the 60 series lead (8.3 +/- 3.6 vs 6.6 +/- 2.3 seconds, P =.04). Moreover, prolonged redetection (>8 seconds) was observed in 41% of patients with 60 series leads compared with only 11% with dedicated bipolar leads (P <.01). No significant effects on redetection were noted with an integrated lead with greater spacing between the tip and coil (70 series). CONCLUSIONS: Delayed redetection is frequently noted with an integrated lead with close spacing between the tip and coil. Detailed evaluation of detection and redetection of these leads should be performed at the time of pulse generator replacement.

Aged↗
PubMed1999

Atrial defibrillation with a transvenous lead: a randomized comparison of active can shocking pathways.

OBJECTIVES: The purpose of this study was to compare transvenous atrial defibrillation thresholds with lead configurations consisting of an active left pectoral electrode and either single or dual transvenous coils. BACKGROUND: Low atrial defibrillation thresholds are achieved using complex lead systems including coils in the coronary sinus. However, the efficacy of more simple ventricular defibrillation leads with active pectoral pulse generators to defibrillate atrial fibrillation (AF) is unknown. METHODS: This study was a prospective, randomized assessment of shock configuration on atrial defibrillation thresholds in 32 patients. The lead system was a dual coil Endotak DSP lead with a left pectoral pulse generator emulator. Shocks were delivered either between the right ventricular coil and an active can in common with the proximal atrial coil (triad) or between the atrial coil and active can (transatrial). RESULTS: Delivered energy at defibrillation threshold was 7.1 +/- 6.0 J in the transatrial configuration and 4.0 +/- 4.2 J in the triad configuration (p < 0.005). Moreover, a low threshold (< or = 3 J) was observed in 69% of subjects in the triad configuration but only 47% in the transatrial configuration. Peak voltage and shock impedance were also lowered significantly in the triad configuration. Left atrial size was the only clinical predictor of the defibrillation threshold (r = 0.57, p < 0.002). CONCLUSIONS: These results indicate that low atrial defibrillation thresholds can be achieved using a single-pass transvenous ventricular defibrillation lead with a conventional ventricular defibrillation pathway. These data support the development of the combined atrial and ventricular defibrillator system.

Aged↗
PubMed1999

Tachycardia induced tachycardia: case report of right ventricular outflow tract tachycardia and AV nodal reentrant tachycardia.

Tachycardia induced tachycardia, or so called double tachycardia, is rare. A 34 year old woman is described who had a history of syncope, frequent extrasystoles, and episodes of non-sustained ventricular tachycardia, perceived as palpitation, without syncope. At electrophysiological study, during infusion of isoprenaline, an episode of non-sustained ventricular tachycardia arising from the right ventricular outflow tract initiated sustained atrioventricular nodal reentrant tachycardia, thought to be the cause of the patient's syncope. Ablation of the right ventricular outflow tract focus abolished the ventricular ectopy; the slow AV nodal pathway was also ablated. The patient no longer has either syncope or palpitation.

Adult↗
PubMed1999

Measurement of intercellular electrical coupling in guinea-pig detrusor smooth muscle.

PURPOSE: The electrical impedance of detrusor smooth muscle strips to alternating current has been measured to calculate the resistance of the intracellular pathway, in particular gap junction resistance. Values have been compared with myocardium, which is electrically well-coupled. MATERIALS AND METHODS: Alternating current was passed along the intracellular pathway of muscle strips by creating a high extracellular resistance around the preparation. The data were analyzed in terms of an equivalent circuit consisting of an intracellular and extracellular pathway. RESULTS: Intracellular resistance was divided into two series components, a cytoplasmic resistance and a gap junction resistance. Detrusor intracellular resistance was about three times that of myocardium. The greater value was attributed to a larger gap-junction resistance. Superfusion of detrusor strips with an isosmotic solution of 50% sucrose, 50% Tyrode's increased both cytoplasm and gap junction resistances. CONCLUSIONS: Gap-junction resistance is larger in detrusor compared with myocardium. However, significant electrical current can still pass between adjacent detrusor cells. Calculation of the space constant however shows that functionally detrusor is electrically well-coupled because of the high membrane resistance. The functional consequences of these findings are discussed.

Animals↗
PubMed1998

Inappropriate shocks from implanted cardioverter defibrillators caused by sensing of diaphragmatic myopotentials.

Inappropriate shocks remain one of the major problems associated with the use of implantable cardioverter defibrillators (ICD). We describe 3 patients who had inappropriate shocks due to oversensing of diaphragmatic myopotentials. In all 3, oversensing could be demonstrated during deep inspiration or Valsalva maneuver. The problem was remedied in one by insertion of a separate rate sensing lead in the right ventricular outflow tract, in the second by decreasing the rate of antibradycardia pacing of the ICD, and in the third by decreasing the sensitivity of the ICD. We conclude that the possibility of sensed diaphragmatic myopotentials should be considered at the time of ICD implant so that appropriate preventive measures can be taken.

Aged↗
PubMed1998

Implications and treatment of atrial fibrillation after cardiothoracic surgery.

Atrial fibrillation (AF) is the most commonly encountered arrhythmia that occurs after cardiothoracic surgery. It develops in up to 40% of patients, most frequently in the first few postoperative days. The strongest risk factors for AF are age and male gender. The pathogenesis of this arrhythmia probably involves increased sympathetic activity in the setting of slowed atrial conduction. The development of postoperative AF is associated with an increased morbidity, higher costs, and prolonged hospitalization. The use of prophylactic beta-blockers and procainamide reduces the incidence of AF whereas digoxin, verapamil, and amiodarone appear less effective. Once AF occurs, the mainstay of treatment remains rate control, anticoagulation, and restoration of sinus rhythm.

Adrenergic beta-Antagonists↗
PubMed1998

Conduction velocity and gap junction resistance in hypertrophied, hypoxic guinea-pig left ventricular myocardium.

The passive and active electrical properties of left ventricular myocardium were measured, using conducted action potentials and current clamp of isolated myocytes. The objective was to quantify changes of intracellular resistivity, Ri, during hypertrophic growth and the simultaneous imposition of cellular hypoxia. Ri was estimated from the time course of the rising phase of a conducted action potential using a solution of the two-dimensional cable equation. The thoracic aorta of guinea-pigs was constricted to induce left ventricular hypertrophy (LVH) and myocardium used 50 and 150 days post-operation. Conduction velocity increased in the earlier stage of LVH and declined in the later stage, compared with age-matched controls. Hypoxia reduced conduction velocity in all experimental groups. Ri increased only in the later stage of hypertrophy (253 +/- 39 Omega cm to 544 +/- 130 Omega cm) and was additionally increased by hypoxia in all groups (e.g. control myocardium 252 +/- 39 Omega cm to 506 +/- 170 Omega cm). The magnitude of the increase of Ri in hypertrophied, hypoxic myocardium can create conditions required to generate re-entrant arrhythmias.

Action Potentials↗
PubMed1997

Changes in cell-to-cell electrical coupling associated with left ventricular hypertrophy.

The impedance to current flow in the intracellular compartment of guinea pig left ventricular myocardium was measured at 20 degrees C and 37 degrees C using tissue from hypertrophied hearts subjected to aortic constriction. Alternating current of varying frequency was passed longitudinally along myocardial preparations, which revealed two time constants: one attributed to the surface membrane at the ends of the preparation and a second lying in the intracellular pathway. The longitudinal impedance was quantitatively analyzed in terms of a parallel intracellular and extracellular pathway; the former had two series components, one attributable to the sarcoplasm and the other to the low-resistance junctions between adjacent cells. This interpretation was consistent (1) with control experiments using n-heptanol, which increased the component attributed to intercellular junctions but not sarcoplasmic resistivity, and (2) with suspensions of isolated myocytes, which yielded a similar value for the sarcoplasmic resistivity. Aortic constriction increased the heart weight-to-body weight ratio of experimental animals from a mean value of 3.10 +/- 0.28 to 5.05 +/- 0.83 g/kg after 50 days of constriction and 5.60 +/- 0.95 g/kg after 150 days of constriction. An increase of heart weight-to-body weight ratio at 150 days of constriction was associated with an increased intracellular resistivity, which could be attributed solely to an increase of the junctional resistance between adjacent cells by approximately 44% at 20 degrees C and 140% at 37 degrees C; the sarcoplasmic resistivity was unchanged. The results are discussed in terms of altered conduction in hypertrophied myocardium as a possible basis for arrhythmias in this tissue.

Alcohols↗
PubMedDate not supplied

Cardiac arrests at the Cenotaph.

This report describes the case histories of three veterans who suffered cardiac arrests at the 2005 Cenotaph Remembrance Parade. All three were successfully resuscitated and admitted to the St Thomas' Hospital Coronary Care Unit. They had internal cardioverter defibrillators (ICDs) inserted and remain well. All three plan to attend Remembrance ceremonies this year. We review the evidence between emotional stress and arrhythmias and the updated National Institute for Health and Clinical Excellence (NICE) guidelines for ICDs.

Aged↗