Table 2.

Comparison between systemic and direct opsin delivery.

Systemic delivery		Direct intramyocardial delivery
+	−	+	−
Uniform	(i) To be specific, it requires a vector with cardiac tropism and/or promoters (ii) Requires high concentrations to achieve uniform expression due to intravascular dilution (iii) Extracardiac expression (iv) Possible immune reaction (v) Cannot be used to achieve local myocardial expression	(i) Lower viral dose required (ii) Increased transduction (iii) Lower incidence of immune response	(i) Inhomogeneous distribution (inefficient if cardiac defibrillation is desired)